Total Prostate-specific Antigen Assays Research Articles

A Comparative Study of Prostate Specific Antigen (PSA) Point-of-Care-Testing (POCT) Techniques

Background: Prostate Specific Antigen (PSA) testing is widely used to diagnose and monitor clinical progress in patients with prostate cancer. The availability of various new Point-of-Care-Testing (POCT) equipment for PSA demands that the performance characteristics of these equipment be assessed before introducing them into clinical use to ensure accuracy and reliability. Objectives: To compare the i-CHROMA® automated immunofluorescence serum total PSA assay with the Accubind® Enzyme Linked Immuno-Sorbent Assay (ELISA) as POCT among patients with suspected prostate cancer. Methods: The study was conducted at the Obafemi Awolowo University Teaching Hospitals Complex (OAUTHC), Ile-Ife, Nigeria. Blood samples drawn from 20 consecutively selected patients were analysed for PSA using the i-CHROMA® immunofluorescence kit once and with the Accubind® ELISA protocol twice. Results: The mean PSA using Accubind® ELISA was 12.9ng/ml, while it was 14.5ng/ml with the i-CHROMA® immunofluorescence assay. The bias between the two methods was 1.6ng/ml. The two methods had a good correlation: Passing Bablok regression equation was y = 1.264604x – 0.0300469, and the Spearman correlation coefficient between the two measurements was high (r = 0.956; Confidence Interval 0.889 - 0.983; p<0.0001). Agreement between the two methods was statistically satisfactory as the mean values of the samples fell within the 95% Confidence Interval of the differences on the Bland Altman plot. Conclusion: The i-CHROMA® POCT assay showed good correlation and agreement with the well-known ELISA method. Therefore, the method is recommended for use in monitoring PSA in patients with prostatic cancer.

Highly portable quantitative screening test for prostate-specific antigen at point of care.

Prostate cancer (PCa) is the second most diagnosed cancer among men. Targeted PCa screening may decrease PCa-specific mortality. Prostate-specific antigen (PSA) is the most reliable and widely accepted tumor biomarker for screening and monitoring PCa status. However, in many settings, quantification of serum PSA requires access to centralized laboratories. In this study, we describe a proof-of-concept rapid test combined with a highly portable Cube™ reader for quantification of total PSA from a drop of serum within 20 min. We demonstrated the application of gold nanoshells as a label for lateral flow assay with significant increase in the measured colorimetric signal intensity to achieve five times lower detection limit when compared to the traditionally used 40 nm gold nanosphere labels, without a need for any additional signal amplification steps. We first optimized and evaluated the performance of the assay with commercially available total PSA calibrators. For initial validation with commercially available ACCESS Hybritech PSA calibrator, a detection range of 0.5–150 ng/mL was achieved. We compared the performance of our total PSA test with IMMULITE analyzer for quantification of total PSA in archived human serum samples. On preliminary testing with archived serums samples and comparison with IMMULITE total PSA assay, a correlation of 0.95 (p < .0001) was observed. The highly portable quantitative screening test for PSA described in this study has the potential to make PCa screening more accessible where diagnostic labs and automated immunoassay systems are not available, to reduce therapeutic turnaround time, to streamline clinical care, and to direct patient care for both initial screening and for post-treatment monitoring of patients.

Analyse des prescriptions de PSA total et libre en France entre 2012 et 2014

In 2010, the French Haute Autorité de santé (National Health Authority) confirmed the limited value of prostate cancer (PCa) screening by total prostate-specific antigen (PSA) assay. This study was designed to determine the modalities of ordering total PSA or free PSA assays (in the absence of PCa) according to various parameters and the corresponding sums reimbursed. Men aged 40years and older covered by the national health insurance general scheme (73% of the French population) between 2012 and 2014 were selected. Data were derived from the Système national d'information inter-régimes de l'assurance maladie (Sniiram) (National health insurance information system) database. In 2014, 27% of the 11.6million men 40years and older underwent at least one total PSA assay and 5.6% underwent at least one free PSA assay, with marked variations according to the presence or absence of treated lower urinary tract symptoms (LUTS) (53% and 15% vs 24% and 5%) and from one administrative department to another. The peak total PSA assay rate was observed between the ages of 65 and 74years: 64% of men with LUTS, 46% without LUTS. Between 2012 and 2014, men in whom at least one PSA assay had been performed underwent a mean of 1.8 total PSA assays and 1.7 free PSA assays, with means of 2.3 and 2, respectively, in the presence of LUTS. General practice specialists ordered 91% of the PSA tests reimbursed in 2014 (92% for total PSA and 87% for free PSA) and urologists ordered 4% of reimbursed tests. The total sum reimbursed was €28.5million, comprising €8.7million for free PSA. An average of 10laboratory tests was performed at the same time as the PSA assay in the absence of treated LUTS. Total PSA and free PSA assays are performed in a large number of men, although the value of these tests as first-line test before biopsy remains controversial. These PSA assays are associated with many other laboratory tests looking for possible abnormalities, especially in younger men, and their relevance may therefore not be specifically discussed with the patient.

The Single-parameter, Structure-based IsoPSA Assay Demonstrates Improved Diagnostic Accuracy for Detection of Any Prostate Cancer and High-grade Prostate Cancer Compared to a Concentration-based Assay of Total Prostate-specific Antigen: A Preliminary Report

BackgroundIsoPSA is a serum-based assay that predicts prostate cancer (PCa) risk by partitioning isoforms of prostate-specific antigen (PSA) with an aqueous two-phase reagent. ObjectivesTo determine the diagnostic accuracy of IsoPSA in identifying the presence or absence of PCa and the presence of high-grade disease in a contemporary biopsy cohort. Design, setting, and participantsMulticenter prospective study of 261 men scheduled for prostate biopsy at five academic and community centers in the USA enrolled between August 2015 and December 2016. InterventionPerformance of the IsoPSA assay. Outcome measurements and statistical analysisDiscrimination power was evaluated using receiver operating characteristic (ROC) analysis. The outcome of the IsoPSA assay was transformed into risk probability using logistic regression. Decision curve analysis (DCA) was used to compare the net benefit of IsoPSA against other clinical protocols. Results and limitationsThe overall prevalence was 53% for any PCa and 34% for high-grade PCa. The area under the ROC curve was 0.79 for any cancer versus none and 0.81 for high-grade PCa versus low-grade PCa/benign histology. In this preliminary study, DCA revealed a superior net benefit of IsoPSA against no biopsy, all biopsy, and the modified Prostate Cancer Prevention Trial Risk Calculator 2.0. At a cutoff selected to recommend biopsy, IsoPSA demonstrated a 48% reduction in false-positive biopsies; at a cutoff selected to identity men at low risk of high-grade disease, there was a 45% reduction in the false-positive rate. ConclusionThe structure-based IsoPSA assay outperformed concentration-based PSA measurement, and provided a net benefit against other protocols. Once validated, clinical use of IsoPSA could significantly reduce unnecessary biopsies while identifying patients needing treatment. Patient summaryThe IsoPSA assay outperformed prostate-specific antigen in predicting the overall risk of prostate cancer and the risk of clinically significant cancer in a preliminary study. The IsoPSA assay could assist in determining the need for prostate biopsy for patients.

Abstract 2012: Accurate measurement of free and complexed PSA concentrations in serum of women using a novel technology with fg/mL sensitivity

Abstract Measurement of free and complexed PSA (prostate specific antigen; complexed with ACT) in certain patient groups such as prostatectomy patients and women at risk of breast and ovarian cancer has been limited by the sensitivity of current immunoassay technology (5-30 pg/mL for common clinical analyzers). Fifth generation assays for total PSA with detection limits of 0.05 to 0.1 pg/mL have been described (McDermet 2009; Thaxton 2009; Wilson 2011). We developed a next-generation assay format based on MSD's MULTI-ARRAY® electrochemiluminescence technology with detection limits of 2 fg/mL (0.002 pg/mL) for complexed PSA (cPSA) and 20 fg/mL for free PSA (fPSA), requiring only 25 μL of serum or plasma per measurement. Assays were calibrated against the WHO standards 96/668 (free PSA) and 98/670 (90% complexed, 10% free PSA). The dynamic range of both assays was three to four orders of magnitude. Typical intra-plate coefficients of variation ranged from 5% to 15%. LLOQ's of cPSA and fPSA assays were 5 fg/mL and 55 fg/mL, respectively. Spike recovery and dilution linearity were between 80% and 120%. Approximately 100 serum samples from women were evaluated. Free PSA was detectable in 95% of samples and cPSA was detectable in all samples. Multiple literature reports indicate that free PSA might be a marker for early detection of breast cancer; however, the concentrations of many samples were close to or below the detection limits of the assays used for the studies. We tested 48 serum samples from patients with breast cancer and 37 serum samples from apparently healthy women. As the table below shows, there was no clear difference between PSA concentrations in cases and controls. Free PSA [fg/mL] (Median, IQR)cPSA [fg/mL] (Median, IQR)Free/cPSA (Median, IQR)Apparently Healthy (n = 37)150 (80-260)560 (210-1,500)0.29 (0.18-0.73)Breast Cancer (n = 48)90 (50-260)180 (90-480)0.36 (0.17-0.77)Breast Cancer, ER positive (n = 10)160 (80-660)170 (120-13,000)0.62 (0.22-1.8)Breast Cancer, HER2 positive (n = 10)160 (50-290)460 (110-8,300)0.10 (0.03-0.44)Breast Cancer, triple negative (n = 10)90 (40-370)140 (50-300)0.68 (0.34-1.9) In conclusion, we developed a next-generation assay format that is 100 to 1000 times more sensitive than the currently available clinical PSA assays. This enables accurate determination of free PSA and cPSA concentrations in the serum of females. Citation Format: Galina N. Nikolenko, Martin K. Stengelin, Laukik Sardesai, Eli N. Glezer, Jacob N. Wohlstadter. Accurate measurement of free and complexed PSA concentrations in serum of women using a novel technology with fg/mL sensitivity. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2012. doi:10.1158/1538-7445.AM2015-2012

Does tenofovir gel or do other microbicide products affect detection of biomarkers of semen exposure in vitro?

ObjectivesThere is currently no information on whether products evaluated in HIV microbicide trials affect the detection of the semen biomarkers prostate-specific antigen (PSA) or Y chromosome DNA. Study DesignWe tested (in vitro) dilutions of tenofovir (TFV), UC781 and the hydroxyethylcellulose (HEC) placebo gels using the Abacus ABAcard and the quantitative (Abbott Architect total PSA) assays for PSA and Y chromosome DNA by real-time polymerase chain reaction. ResultsTFV gel and the HEC placebo adversely affected PSA detection using the ABAcard but not the Abbott Architect total PSA assay. UC781 adversely affected both the ABAcard and Abbott Architect total PSA assays. While there were some quantitative changes in the magnitude of the signal, none of the products affected positivity of the Y chromosome assay. ConclusionsThe presence of TFV or HEC gels did not affect quantitative PSA or Y chromosome detection in vitro. Confirmation of these findings is recommended using specimens obtained following use of these gels in vivo. ImplicationsResearchers should consider the potential for specific microbicides or any products to affect the particular assay used for semen biomarker detection. The ABAcard assay for PSA detection should not be used with TFV UC781, or HEC.

Effect of lubricants and a vaginal spermicide gel on the detection of prostate specific antigen, a biomarker of semen exposure, using a quantitative (Abbott ARCHITECT) assay

ObjectivesLittle is known about the effects of commonly used lubricants on detection of biomarkers of semen exposure. We investigated the in vitro effect of Gynol®, K-Y Jelly®, Replens®, Astroglide®, Carbopol, and Silicorel on quantitative detection of prostate specific antigen (PSA). Study DesignA predetermined concentration of each of the gels was added to serially diluted semen samples. Additionally, serial dilutions of each of the gels were added to three different semen dilutions (high, medium, or low). The resulting samples were tested for PSA on the Abbott ARCHITECT System. ResultsWhen using the Abbott ARCHITECT system, the only products that inhibited PSA detection were Gynol® and Replens®. The inhibition caused by Gynol® was dose-dependent, but that of Replens was dose-independent. K-Y Jelly®-spiked samples had higher PSA values than controls. ConclusionsCaution is warranted when using the Abbott quantitative assay for PSA detection as a biomarker of semen exposure in settings where Gynol®, Replens® or K-Y Jelly® might also have been used. Neither Astroglide® nor Silicorel inhibited PSA detection. Additional studies evaluating other vaginal products, including microbicides, and their effects on other assays, are needed. In vivo studies will be especially important to optimize PSA detection from clinical samples. ImplicationsResearchers should consider the potential for specific lubricants or any vaginal products to affect the particular assay used for semen biomarker detection. The Abbott ARCHITECT’s total PSA assay should not be used with the product Replens. Caution is warranted when using the assay in settings where Gynol or K-Y jelly may have been used.

SERUM PROSTATE SPECIFIC ANTIGEN (PSA);

ABSTRACT… Objective: To study correlation between age-linked serum prostate specific antigen (PSA) levels in normal subjects andpatients of benign prostatic hyperplasia (BPH) and carcinoma prostate (CaP). Data source: OPDs. Study design: Case-control study.Setting: SIUT; Karachi Study duration: Six months. Methodology: 250 subjects were enrolled for the study and 93 were finally selected(31 each, representing the normal, BPH and CaP groups). Subjects 40 years of age and above were included and those with any urinarytract disorder or those under treatment with 5-á-reductase inhibitors were excluded. Each group was divided into four sub-groups of ages40 – 49, 50 – 59, 60 – 69 and 70 and above years. AxSYM total PSA (tPSA) assay® was used for serum PSA estimation. Values wereexpressed as mean and standard error of mean and Fischer’s test, students’ t test and correlation coefficient were used to determinesignificance and for comparison of data. Results: There was a no significant difference in PSA levels in all age groups when normals werecompared with BPH cases. PSA levels were significant in normal as compared to CaP cases and BPH as compared to CaP. Conclusions:No significant correlation between age-linked serum PSA levels in normal subjects and patients of BPH and CaP could be established. Thestudy, however, found a trend of declining PSA levels at the age of 70 years and above.

Nucleic Acid Detection Immunoassay for Prostate-Specific Antigen Based on Immuno-PCR Methodology

Serum prostate-specific antigen (PSA) concentrations after radical prostatectomy typically become undetectable with the use of current immunometric assay methods. Despite modern surgical techniques, 15%-30% of prostate cancer patients undergoing radical prostatectomy develop a biochemical recurrence during follow-up. Unfortunately, poor analytical sensitivity of standard PSA assays delays biochemical recurrence detection, and because of day-to-day assay imprecision ultrasensitive PSA assays cannot assess PSA kinetics. We developed an immuno-PCR assay for total PSA that has a limit of quantification >10 times lower than current ultrasensitive assays. The 2-site immunometric assay for total PSA employed 2 monoclonal antibodies, one conjugated to a double-stranded DNA label and the other bound to paramagnetic microparticles. After several washing steps, quantification cycles were determined and values were converted to PSA concentrations. We characterized analytical performance and compared accuracy with a commercially available total PSA assay. The limit of quantification was 0.65 ng/L and the assay was linear in the range of 0.25-152.0 ng/L. Total imprecision estimates at PSA concentrations of 3.8, 24.1, and 69.1 ng/L were <15.2%, <9.4%, and <10.6%, respectively. Recovery of supplemented PSA ranged from 87.5% to 119.2% (mean 100.3%). Dilution recovery ranged from 96.4% to 115.3% (mean 102.3%). There was no high-dose hook effect up to 50 000 ng/L of PSA. Comparison with the commercial PSA assay showed a regression slope of 1.06 and a correlation coefficient of 0.996. The analytical characteristics of the assay support the use of this assay for the accurate and precise measurement of serum PSA, even at sub-nanogram-per-liter concentrations.

Is the WHO 90:10 Prostate-Specific Antigen (PSA) First International Reference Standard Really 90% α1-Antichymotrypsin–Bound PSA and 10% Free PSA?

To the Editor: Several factors can contribute to differences among immunoassay methods. Such differences have led to a recognition of the need for the standardization of prostate-specific antigen (PSA)1 assays, and 2 Stanford conferences on the international standardization of PSA immunoassays were held in the early 1990s (1, 2). In 1999, the WHO Expert Committee on Biological Standardization established the First International Standards for PSA with materials that emanated from recommendations of these conferences. These materials consisted of lyophilized 1-μg preparations of 100% free PSA (96/668), and 90% α1-antichymotrypsin–bound PSA (PSA-ACT) and 10% free PSA (96/670) (3) (www.nibsc.ac.uk). A preliminary study found that when total and free PSA were measured in solutions of the 90% PSA-ACT and 10% free PSA (90:10 PSA) material from Stanford/WHO, the slope of the regression line that compared the measured free PSA to measured total PSA was 0.15 instead of the expected 0.10 (unpublished data). The objective of the current study was to further investigate this observation by comparing PSA standard materials from 2 sources (Stanford/WHO and Scripps Laboratories) in 4 total and free PSA assays. The Stanford/WHO reference materials (PSA-ACT standard and 90:10 PSA standard; lyophilized, 1 μg/vial) were purchased from Stanford University. Vials were reconstituted with 2 mL deionized water. Free PSA and …

Assessment of noninvasive predictors of bladder outlet obstruction and acute urinary retention secondary to benign prostatic enlargement

PurposeTo prospectively compare the diagnostic accuracy of intravesical prostatic protrusion (IPP), detrusor wall thickness (DWT), prostate volume (PV) and serum prostate specific antigen (PSA) levels for detecting bladder outlet obstruction (BOO) and predicting acute urinary retention (AUR) secondary to benign prostatic obstruction. Patients and methodsIn all, 135 men who presented with lower urinary tract symptoms due to benign prostatic enlargement were enrolled in the study; among them, 50 presented with AUR. Thirty normal men in the same age group were included and represented a control group for normative data. Their evaluation included a digital rectal examination, International Prostate Symptom Score and quality-of-life question, uroflowmetry and serum total PSA assay. Transabdominal ultrasonography was used to measure the PV, IPP DWT and post-void residual urine volume. Pressure-flow urodynamic studies were used as the reference standard test for BOO, differentiating obstructed from unobstructed bladders. DWT, IPP, PV and total PSA level served as index tests. To compare the usefulness of the various indices, the area under the curve (AUC) of receiver-operator characteristic curves was calculated for each index. ResultsAccording to presentation and urodynamic studies, patients were classified into three groups: Group 1 (no BOO), 50 patients with a BOO index (BOOI) of <40; group 2 (BOO), 35 with a BOOI of >40; and group 3 (AUR), 50 who presented with AUR. The IPP, DWT, PV and PSA levels differed significantly between obstructed and unobstructed patients, with a significant correlation with the BOOI. The AUC for IPP, DWT, PSA and PV were 0.885, 0.783, 0.745 and 0.678, respectively. The IPP threshold at 8mm provided the best diagnostic accuracy (80%) for detecting BOO, followed by combined DWT and IPP (77.6%). Between patients with and without AUR, there was a highly significant difference in IPP, DWT and PSA; a combined IPP threshold of >8mm and DWT >2mm detected AUR in 45 of 50 patients (90%). ConclusionAll four noninvasive indices were correlated significantly with BOOI. The IPP as a single variable and combined with DWT predicted BOO and AUR better than PSA or PV.

Discordant total and free prostate-specific antigen (PSA) assays: does calibration with WHO reference materials diminish the problem?

Prostate-specific antigen (PSA) assay-dependent variations could result in misinterpretation of individual PSA values. Therefore, the situation for clinical interpretation of PSA or percent free PSA (%fPSA) results is complicated. This review summarizes the differences in various total PSA (tPSA) and free PSA (fPSA) assays, and results obtained using the new World Health Organization (WHO) calibrated Access assays from various studies. Method comparisons between the traditionally calibrated Hybritech PSA and fPSA assays and the new "standardized" WHO calibrated assays yield results that are approximately 25% lower for PSA and fPSA. A PSA cut-off of 3 or 3.1 microg/L should be considered for WHO calibrated assays in order to achieve the same sensitivity/specificity profile as with a cut-off of 4 microg/L in traditionally calibrated assays. The %fPSA cut-offs could be retained.

Standardization of Prostate-Specific Antigen (PSA) Assays: Can Interchangeability of PSA Measurements Be Improved?

The landscape of prostate cancer has changed since the appearance of the first prostate-specific antigen (PSA) assay. PSA testing has gained rapid recognition since M. Kuriyama et al. (1) of Roswell Park first reported clinical studies using an enzyme immunoassay with anti-PSA rabbit antibody. Mikolajczyk and coworkers (2)(3) reported the presence of several free PSA isoforms and the potential application of free PSA isoforms as serum markers. Today, more than 30 types of total PSA assay reagent sets and ∼10 types of free PSA and PSA–α1-antichymotrypsin (ACT) assays, based on various principles, are available. Key elements in PSA measurement are interchangeability of assays and stability of serum samples before tests (4)(5). Efforts to standardize PSA assays were initiated in 1992 at the First Stanford Conference, organized by T. Stamey. At the Second Stanford Conference on International Standardization of Prostate-Specific Antigen (1994), Stamey et al. (6) proposed a primary calibrator consisting of 90% purified PSA-ACT and 10% free PSA (90:10) on a molar basis. Subsequently, the Clinical and Laboratory Standards Institute (CLSI; formerly NCCLS) issued a document (7) recommending a set of 3 distinct materials containing 100% free PSA, 100% PSA-ACT, and 90% PSA-ACT:10% free PSA. This document led to further activity in the harmonization of PSA assays. In 1999, Robert M. Nakamura, a member of the International Consultation Committee on Prostate Cancer, made recommendations, with his colleagues (8), on standardization and quality assessment of …

Comparison of Fresh Frozen Serum to Proficiency Testing Material in College of American Pathologists Surveys: α-Fetoprotein, Carcinoembryonic Antigen, Human Chorionic Gonadotropin, and Prostate-Specific Antigen

Abstract Context.—Most proficiency testing materials (PTM) contain an artificial matrix that may cause immunoassays to perform differently with this material than with clinical samples. We hypothesized that matrix effects would be reduced by using fresh frozen serum (FFS). Objective.—To compare the performance of an FFS pool to standard PTM for measurement of α-fetoprotein, carcinoembryonic antigen, human chorionic gonadotropin (hCG), and prostate-specific antigen (PSA). Design.—One FFS specimen and 4 different admixtures of PTM were distributed in the 2003 College of American Pathologists K/KN-A (for α-fetoprotein, carcinoembryonic antigen, hCG, and total and free PSA) and C-C (hCG only) Surveys. Participants.—The number of laboratories that participated in the surveys varied from a low of 288 (free PSA, K/KN-A Survey) to a high of 2659 (hCG, C-C Survey). Main Outcome Measures.—Method imprecision and method bias were compared between the FFS specimen and the standard PTM specimen with the closest value. Method imprecision was determined by calculating the coefficients of variation for each method and for all methods combined. Bias was defined as the proportional difference between peer-group mean and the median of all method means. Results.—The FFS specimen gave significantly higher imprecision than PTM for the analytes α-fetoprotein, carcinoembryonic antigen, total PSA, and free PSA. For hCG, no substantial imprecision differences were observed in both surveys. Bias was significantly greater for the α-fetoprotein, carcinoembryonic antigen, and total PSA assays and significantly lower for the hCG and free PSA assays when comparing the FFS with the PTM. Conclusions.—Fresh frozen serum did not provide consistently lower imprecision or bias than standard PTM in a survey of commonly ordered tumor markers.

Use of Percent Free Prostate-Specific Antigen Density to Improve the Specificity for Detecting Prostate Cancer in Patients with Normal Rectal Examinations and Intermediate Prostate-Specific Antigen Levels

Introduction: As prostatic volume influences percent free prostate-specific antigen (PSA) in patients with prostate cancer, we evaluated whether percent free PSA density, which relates the serum percent free PSA to the volume of the prostate determined by transrectal ultrasound, could increase the specificity of cancer detection in men with normal digital rectal examinations and intermediate PSA levels. Materials and Methods: We prospectively evaluated 105 consecutive men with normal digital rectal examinations and serum PSA levels of 4.1–10.0 ng/ml. All patients underwent at least sextant prostate biopsies to establish the diagnosis. For detection of total and free PSA we used an Immulite free and total PSA assay. We compared PSA density, percent free PSA and percent free PSA density for their utility in cancer detection. Results: Overall, 20 of 105 patients (19%) had prostate cancer. The area under the curve (AUC) for percent free PSA density was 0.771, not significantly higher than the AUC of 0.75 for PSA density (p = 0.778), but significantly higher than the AUC of 0.604 for percent free PSA (p = 0.021). Of these three parameters, percent free PSA density yielded the highest specificity percentage (54.1%) at 95% sensitivity. Conclusions: Percent free PSA density is more specific than percent free PSA in distinguishing benign from malignant disease in men with a normal digital rectal examination and an intermediate PSA level. Further study is necessary to discover whether percent free PSA density is superior to percent free PSA or PSA density.

Combining free and total prostate specific antigen assays from different manufacturers: the pitfalls.

We investigated the impact of interchanging free prostate specific antigen (f-PSA) concentrations from 10 different assays over a reference total PSA (t-PSA) on predicting prostate histology with free-to-total PSA ratios (f/t-PSA). Archival sera from 80 t-PSA- and age-matched pairs of histologically confirmed prostate cancer (PCA) and benign prostatic hyperplasia (BPH) patients with t-PSA levels between 2 and 25 microg/l were investigated. Serum aliquots were analyzed for t- and f-PSA using a reference method (Access, Beckmann-Coulter Hybritech) and 10 commercially available f-PSA assays. Passing Bablok and linear regression were performed to investigate the interassay agreement between f-PSA assays. To compare diagnostic performance, ROC curves for PCA detection were calculated for the 10 f/t-PSA combinations using the reference t-PSA as denominator. Sensitivities, specificities and f/t-PSA cut-offs were calculated for varying points of the ROC curve. Despite good correlation of all 10 f-PSA assays with the reference method 4 showed significantly lower mean f-PSA levels. For f/t-PSA as a predictor of prostate histology, areas under the ROC curve (AUC) varied between 0.65 and 0.71 and, if compared to the reference method (AUC=0.70), were significantly lower in three cases. Ensuring 80% specificity, sensitivities ranged between 34% and 54% (reference method: 53%) and f/t-PSA cutpoints differed considerably depending on the f-PSA assay used (range: 0.15-0.24; reference: 0.15). Similar variations were noted at 95% specificity and 80% and 95% sensitivity. Arbitrary combinations of f- and t-PSA assays should not be used to calculate f/t-PSA ratios unless adequate studies have validated the diagnostic performance and cut-offs of that particular assay choice.

Clinical Evaluation of the Elecsys Total Prostate-specific Antigen Assay on the Elecsys 1010 and 2010 Systems

Prostate cancer (PCa) is a leading cause of cancer-related deaths. The American Cancer Society expects >198 000 newly diagnosed cases and 31 500 deaths related to PCa in the US in 2001 (1). The indolent clinical course of PCa makes its early detection a challenge. Symptoms typically do not occur until PCa is locally advanced or metastasized, at which time cure is not usually possible. Early detection is therefore mandatory to reduce the mortality of PCa. Prostate-specific antigen (PSA) is a serine protease synthesized in prostatic epithelium. Introduced into clinical use in the late 1980s (2), PSA today is recognized as the most useful tumor marker in urologic oncology and as indispensable for early detection, staging, and monitoring of PCa (3). Digital rectal examination (DRE) alone has a poor sensitivity of 2.2–25% (4)(5) and specificity of 39% (6) in detecting PCa. Measurement of serum PSA concentrations in combination with DRE markedly improves the detection of PCa and increases the lead time for diagnosis (4)(5). This clinical study was designed to demonstrate the clinical utility of the newly developed Roche Diagnostics Elecsys® total PSA Assay on the Roche/Hitachi Elecsys 2010 and 1010 systems. This assay is a quantitative in vitro diagnostic test for detection of total PSA (tPSA) and is indicated for measurement of tPSA in combination with DRE to aid in the diagnosis of PCa. A total of 1121 serum samples for PSA analysis were prospectively taken from men referred for urologic evaluation (mean age, 66 years; range, 50–91 years). DRE was performed by urologists. Symptoms leading to referral were, e.g., voiding dysfunction, lower back pain, or perineal discomfort. No previous PSA values were available, nor had any patient undergone a previous biopsy. No DRE was performed <15 days and no medical …

Comparative Analysis of Complexed Prostate Specific Antigen, Free Prostate Specific Antigen and Their Ratio in Detecting Prostate Cancer

We evaluate the diagnostic use of total, free and complexed serum prostate specific antigen (PSA), and their ratios for enhancing the specificity in detecting prostate cancer. A total of 354 nonconsecutive men undergoing prostate biopsy were eligible for this retrospective and prospective study. Cancer was found in 122 of these 354 men (34%). Receiver operating characteristics curve analyses were used to calculate and compare the performance of total PSA (Hybritech, San Diego California and Bayer, Tarrytown, New York), complexed PSA (Bayer), percent complexed PSA and percent free PSA. In addition, sensitivity and specificity were calculated and compared. The area under the receiver operating characteristics curve was highest for percent free PSA, followed by percent complexed PSA, complexed PSA and the 2 total PSA assays (Hybritech and Bayer). The cutoff value of 3.45 ng./ml. for complexed PSA detected the same number of cancers and resulted in 1 additional false-positive case compared with a Hybritech total PSA threshold of 4.0 ng./ml. At sensitivities of 80% to 95%, there were no significant differences for detection comparing the corresponding specificities between Hybritech total PSA and complexed PSA for all 354 men. Complexed PSA alone did not enhance the overall diagnostic accuracy compared with percent free PSA in the Hybritech total PSA range between 4.01 and 6.00 ng./ml., between 6.01 and 10.00 ng./ml., and between 2.50 and 6.00 ng./ml. At sensitivities of 80% to 95% specificity of percent complexed PSA was almost identical to that of percent free PSA except for the Hybritech total PSA range less than or equal to 4.00 ng./ml. This study suggests complexed PSA is equivalent to total PSA for the early detection of prostate cancer. Percent free PSA outperforms complexed PSA and percent complexed PSA performed equivalently to percent free PSA in all total PSA ranges analyzed between 2.5 and 10 ng./ml.

Analytical performance of the Roche total and free PSA assays on the Elecsys 2010 immunoanalyzer

Recently, site-specific fucosylation of glycoproteins has attracted attention as it can be associated with several types of cancers including prostate cancer. However, individual glycoproteins, which might serve as potential cancer markers, often are very low-concentrated in complex serum matrices and distinct glycan structures are hard to detect by immunoassays. Here, we present a mass spectrometry-based strategy for the simultaneous analysis of core-fucosylated and total prostate-specific antigen (PSA) in human serum in the low ng/ml concentration range. Sample preparation comprised an immunoaffinity capture step to enrich total PSA from human serum using anti-PSA antibody coated magnetic beads followed by consecutive two-step on-bead partial deglycosylation with endoglycosidase F3 and tryptic digestion prior to LC-MS/MS analysis. The method was shown to be linear from 0.5 to 60 ng/ml total PSA concentrations and allows the simultaneous quantification of core-fucosylated PSA down to 1 ng/ml and total PSA lower than 0.5 ng/ml. The imprecision of the method over two days ranged from 9.7–23.2% for core-fucosylated PSA and 10.3–18.3% for total PSA depending on the PSA level. The feasibility of the method in native sera was shown using three human specimens. To our knowledge, this is the first MS-based method for quantification of core-fucosylated PSA in the low ng/ml concentration range in human serum. This method could be used in large patient cohorts as core-fucosylated PSA may be a diagnostic biomarker for the differentiation of prostate cancer and other prostatic diseases, such as benign prostatic hyperplasia (BPH). Furthermore, the described strategy could be used to monitor potential changes in site-specific core-fucosylation of other low-concentrated glycoproteins, which could serve as more specific markers (“marker refinement”) in cancer research.

Development and validation of a quantitative ELISA for the measurement of PSA concentration

Background: Prostate-specific antigen (PSA) has been used for the diagnosis and follow up of prostate cancer (PCa). Methods: Mouse monoclonal antibodies (MAbs) were generated against human prostate-specific antigen (PSA) for the development of a sensitive total PSA (t-PSA) assay. Two MAbs, denoted CB-PSA.4 and CB-PSA.9, with affinities of 3.7×10 9 and 4.7×10 10 l/mol, respectively, were used to develop an enzyme-linked immunosorbent assay (ELISA) for quantifying serum t-PSA concentration. Results: The detection limit (DL) of the assay was 0.1 μg/l ( n=20, mean of “zero” standard+3S.D.), and the recovery of t-PSA was 96–103%. The within-run and between-day coefficients of variation (CV) ranged from 2.1% to 3.2%, and from 2.8% to 6.3% for PSA concentrations of 10 and 1 μg/l, respectively. The equimolar detection of t-PSA and free-PSA was demonstrated by two different methods, one consisted in the comparative evaluation of a sera panel ( n=9) with our enzyme-linked immunosorbent assay (ELISA) and four commercial total PSA assays and the concordance with CIS bio total PSA assay. The assay had a linear range of 0.12 to 25 μg/l. Conclusions: The analytical performance characteristics of our PSA ELISA suggest that it will provide clinically useful PSA results, particularly when diagnostic algorithms are used.