Measurement Of Total Prostate-specific Antigen Research Articles

Evaluation of the Relationship Between Prostate-Specific Antigen Levels, Gleason Scores, and 68Ga-PSMA PET/CT Scan Findings in Prostate Cancer Patients

Background: The use of 68-gallium prostatespecific membrane antigen positron emission tomography/computed tomography (68Ga-PSMAPET/CT) scan has recently received particular attention in the evaluation of prostate cancer patients. Objectives: The present study aimed to evaluate the relationship between the prostate-specific antigen (PSA) level, Gleason score, and 68Ga-PSMAPET/CT findings in prostate cancer patients. Patients and Methods: In this cross-sectional study, 80 male patients with a definitive diagnosis of prostate cancer, who were candidates for 68Ga-PSMA PET/CT scan for both initial staging and restaging, were included. Restaging indicated biochemical recurrence, which refers to a detectable level of PSA after being documented undetectable following a definitive primary treatment. All prostate cancer patients, who were not initially treated with a definitive therapy, were excluded from the study. A cutoff value ≥ 4 was considered significant for maximum standardized uptake value (SUVmax) to differentiate benign from malignant 68Ga-PSMA-avid lesions. Any 68Ga-PSMA uptake outside the prostate bed, especially in the lymph nodes, bones, and visceral organs, was considered metastatic. Results: Comparison of the PSA level between two subgroups with and without metastasis demonstrated a higher PSA level in patients with metastatic abdominal lymph nodes and a slightly higher PSA level in patients with metastatic pelvic lymph nodes. No significant correlation was found between the Gleason score and the total PSA. There was also no significant association between the level of PSA and the type of Lymph node involvement (single or multiple) in different involved areas. Besides, there was no significant correlation between the SUVmax and the level of PSA and the Gleason score in different involved areas. Conclusion: The SUVmax value in 68Ga PSMA PET/CT scan provides a reliable predictor for neither the grade of prostate cancer, nor the metastatic status associated with cancer progression. The measurement of total PSA may predict metastasis to the abdominal and pelvic lymph nodes caused by prostate cancer.

Determination of Free-PSA (fPSA) and fPSA/PSA-Ratio Using A Point-of-Care Device.

Prostate specific antigen (PSA) and free PSA (fPSA) are important tools for diagnosing prostate cancer (PC). Efforts are continuously undertaken to provide more patient-centered healthcare. The application of point-of-care (POC) systems for laboratory analyses represents a step in this direction. Previous investigations on total PSA measurements using a POC system (concile® Ω100 POC reader) showed good concordance with standard laboratory measurements. For the same POC reader a novel system for fPSA was developed. In the current study, we prospectively evaluated the quality of the POC system for fPSA. Sixty-four patients undergoing PSA measurements in our outpatient clinic between 06/2015 and 09/2015 were enrolled in the study. We measured total PSA (tPSA) and fPSA with a POC reader system (concile® Ω100) and a standard laboratory system (Siemens Immulite 2000®) and compared the respective results using linear regression analyses for PSA, fPSA, and fPSA/tPSA ratio (%fPSA). The coefficients of determination (r²) for fPSA and %fPSA were 0.85 (p < 0.001) and 0.82 (p < 0.001) in the subgroup with total PSA between 4 and 10 ng/mL. In the subgroup with tPSA ≤ 4 ng/mL, r² for fPSA concile® was 0.55 (p < 0.001) and 0.10 (p = 0.088) for %fPSA. In the subgroup of tPSA > 10 ng/mL the r² for fPSA and %fPSA was 0.50 (p = 0.022) and 0.50 (p = 0.022), respectively. The POC fPSA values correlated well with the laboratory analyses, specifically in the clinically relevant diagnostic range of tPSA 4 - 10 ng/mL. These results complement the tPSA data obtained previously and indicate the reliability of the fPSA method and the resulting %fPSA score.

Comparability of serum total prostate-specific antigen measurement by four domestic chemiluminescence immunoassays and electrochemiluminescence immunoassay

Objective To study the comparability of total prostate specific antigen (tPSA) measurement by four domestic chemiluminescence immunoassays (DCI) and electrochemiluminescence immunoassay (ECI). Methods A total of 45 serum samples that requested tPSA tests were selected. Four DCIs (Snibe MAGLUMI 4000, Mindray CL-2000i, Autobio A2000, HYBIOME AE180) and ECI (Roche Cobas e601) were used to measure tPSA. The precisions of the methods were evaluated. The four DCIs were compared with Roche ECI respectively, and the comparability of the test results was analyzed. Wilcoxon signed rank test and Spearman correlation analysis were used to analyze the data. Results The precisions of five methods were good. The tPSA levels measured by Roche Cobas e601, Snibe MAGLUMI 4000, Mindray CL-2000i, Autobio A2000, and HYBIOME AE180 were 14.11(9.92, 36.09), 12.00(8.56, 27.23), 12.10(8.60, 29.87), 13.35(9.51, 32.85) and 14.50(9.88, 40.06) μg/L, respectively. The correlation coefficients of Roche with Snibe MAGLUMI 4000, Mindray CL-2000i, and Autobio A2000 were 0.992, 0.989, 0.957 and 0.983, respectively (all P<0.001). Assuming the tPSA medical decision point for regression equation was 4.0 μg/L, the proportional biases of Snibe MAGLUMI 4000, Mindray CL-2000i, Autobio A2000, and HYBIOME AE180 compared with Roche were -10.88%, -18.07%, 0.23% and 22.31%, respectively. Conclusion The comparability of tPSA test results is different between 4 DCIs and Roche ECI, which provides some references for clinical application and standardization of the DCI test results. Key words: Prostate-specific antigen; Chemiluminescent measurements; Immunoassay

Performance of the 4Kscore Test in Plasma and Serum and Stability of the Component Analytes in Clinical Samples.

The 4Kscore Test determines a personalized risk score for aggressive prostate cancer by combining the blood sample measurements of total prostate-specific antigen (tPSA), free PSA (fPSA), intact PSA (iPSA), and human kallikrein-related peptidase 2 (hK2) with patient clinical information to generate the patient risk's score; thus, accuracy and precision of the 4Kscore depend on the reliability of these measurements. Although tPSA and fPSA are measured on a Food and Drug Administration (FDA)-approved platform, the performance of the iPSA and hK2 assays in the clinical setting has not previously been reported. Analytical performance was determined for the iPSA and hK2 assays in both serum and EDTA plasma, according to Clinical and Laboratory Standards Institute guidelines. Equivalence of the 4Kscore in both sample matrices was demonstrated in a 353-patient clinical cohort, and the stability of endogenous iPSA and hK2 for at least 3 days was demonstrated in a smaller subset. Intralaboratory and interlaboratory precision of the iPSA and hK2 assays in both matrices was comparable with that of FDA-approved tPSA and fPSA assays (<18% for iPSA; <8% for hK2). The picogram per milliliter sensitivity and wide dynamic range of the iPSA and hK2 assays allowed for accurate measurements in the target population. The 4Kscore generated in either matrix up to 3 days after collection is equivalent to that measured within 24 h of collection (Passing-Bablok slope 95% CI: plasma, 0.999-1.034; serum, 0.997-1.040). The robust performance of component assays and reliable stability of the endogenous analytes in clinical samples proven here ensures an accurate 4Kscore Test result.

The Ability of Prostate Health Index (PHI) to Predict Gleason Score in Patients With Prostate Cancer and Discriminate Patients Between Gleason Score 6 and Gleason Score Higher Than 6-A Study on 320 Patients After Radical Prostatectomy.

Aim:The purpose of this study was to investigate the Prostate Health Index as a marker for tumor aggressiveness in prostate biopsy and the optimization of indication for treatment options.Methods:Our cohort consisted of 320 patients indicated for radical prostatectomy with preoperative measurements of total prostate-specific antigen, free prostate-specific antigen, [-2]proPSA, calculated %freePSA, and Prostate Health Index. The Gleason score was determined during biopsy and after radical prostatectomy. Using the Gleason score, we divided the group of patients into the 2 subgroups: Gleason score ≤6 and Gleason score >6. This division was performed according to the biopsy Gleason score and according to the postoperative Gleason score. We compared total prostate-specific antigen, [-2]proPSA, %freePSA, and Prostate Health Index in the subgroups Gleason score ≤6 and Gleason score >6 after biopsy and the definitive score.Results:On evaluation of the subgroups created by Gleason score ≤6 and Gleason score >6, we observed agreement between biopsy Gleason score and definitive Gleason score in only 45.3% of cases. Of the calculated biopsy, Gleason score ≤6 and Gleason score >6 subgroups, [-2]proPSA, and Prostate Health Index (P = .0003 and P = .0005) were statistically significant. Of the definitive Gleason score ≤6 and Gleason score >6 subgroups, Prostate Health Index, [-2]proPSA, %freePSA, and PSA (P < .0001, P < .0001, P = .0003, and P = .0043) were statistically significant. The best area under the curve value (0.7496) was achieved by Prostate Health Index when the subgroups were established according to the postoperative Gleason score.Conclusion:Prostate Health Index is the best of the tested markers for the categorization of Gleason score 6 tumors and for facilitating the management of patients with prostate cancer. Prostate Health Index can be a helpful marker for indication of active surveillance or radical prostatectomy. Prostate health index can also simplify the decision of whether to perform nerve-sparing radical prostatectomy.

Dual-labeled chemiluminescence enzyme immunoassay for simultaneous measurement of total prostate specific antigen (TPSA) and free prostate specific antigen (FPSA).

The specificity for early diagnostic of prostate-specific antigen (PSA) is low because the current technology mostly allows the detection of only one biomarker at one time. In this work, a dual-labeled chemiluminescence enzyme immunoassay (CLEIA) for simultaneous measurement of total PSA (TPSA) and free PSA (FPSA) was proposed. Anti-PSA McAb (Mab1) was immobilized on a microplate as the solid phase, horseradish peroxidase (HRP)-labeled anti-TPSA monoclonal antibody (McAb2) and alkaline phosphatase (ALP)-labeled anti-FPSA McAb3 were used as detection antibodies. Two chemiluminescence reactions of HRP with luminol and ALP with 4-methoxy-4-(3-phosphate-phenyl)-spiro-(1,2-dioxetane-3,2'-adamantane) (AMPPD) were used as the signal detecting system. Based on a sandwich model, the amount of FPSA and TPSA could be determined simultaneously. The effects of several physico-chemical parameters were studied and optimized. Cross-reactivities of six common tumor markers in serum were studied. The proposed method presented the sensitivity of 0.03ng ml-1 and 0.05ng ml-1 for FPSA and TPSA respectively, with low cross-reactivities. Compared with the results from commercial chemiluminescent kits there was good correlation, indicating that this established method could be used to simultaneously to measure the concentrations of FPSA and TPSA in one serum sample and also could greatly facilitate the early diagnosis for PCa in clinical practice.

DIAGNOSTIC VALUE OF DEFINITION OF FRACTIONS OF PROSTATIC SPECIFIC ANTIGEN AND PROSTATE HEALTH INDEX

OBJECTIVE. The authors investigated the value of comprehensive assessment of clinical and laboratory factors including prostate specific antigen (PSA) fractions and prostate health index (PHI) in diagnostics of prostate cancer. MATERIALS AND METHODS. The study numbered 148 patients who were examined for suspected prostate cancer. Clinicians made the measurement of total PSA and fractions, PHI, multifocal transrectal biopsy of prostate. The statistical data were analyzed. RESULTS. The formulas obtained used the discriminant analysis of all clinical and laboratory factors (PSA fractions and PHI). These formulas showed the high possibility (77-80 %) to predict the presence of prostate cancer with sensitivity 70-78 % and specificity 77-83 %. Percentage of [-2]proPSA depended on PHI value and had the significant influence on the possibility of prostate cancer detection.

Accuracy of PCA3 Measurement in Predicting Short-Term Biopsy Progression in an Active Surveillance Program

PCA3 is a prostate specific noncoding mRNA that is significantly over expressed in prostate cancer tissue. Urinary PCA3 levels have been associated with prostate cancer grade and extent, suggesting a possible role in monitoring patients on active surveillance. We assessed the relationship between PCA3 and prostate biopsy results in men in a surveillance program. Urine specimens were obtained from 294 men with prostate cancer enrolled in the Johns Hopkins surveillance program. The followup protocol included semiannual free and total prostate specific antigen measurements, digital rectal examination and annual surveillance prostate biopsy. Cox proportional hazards regression was used to evaluate the association between PCA3 results and progression on surveillance biopsy (defined as Gleason pattern 4 or 5, more than 2 positive biopsy cores or more than 50% involvement of any core with cancer). Patients with progression on biopsy (12.9%) had a mean PCA3 score similar to that of those without progression (60.0 vs 50.8, p = 0.131). ROC analysis suggested that PCA3 alone could not be used to identify men with progression on biopsy (AUC 0.589, 95% CI 0.496-0.683, p = 0.076). After adjustment for age and date of diagnosis PCA3 was not significantly associated with progression on biopsy (p = 0.15). In men with low risk prostate cancer who were carefully selected for surveillance the PCA3 score was not significantly associated with short-term biopsy progression. Further analysis is necessary to assess the usefulness of PCA3 in combination with other biomarkers or in selected subsets of patients undergoing surveillance.

Assay Standardization Bias: Different Prostate Cancer Detection Rates and Clinical Outcomes Resulting from Different Assays for Free and Total Prostate-Specific Antigen

Numerous commercial assays are available for measuring total and free prostate-specific antigen (PSA) levels in serum. These assays can be referenced to different laboratory standards, and interassay variability occurs. Patients and physicians might be affected by the variability between PSA assays that results from the use of different PSA standards. We prospectively compared the free and total PSA measurements obtained using two commercially available PSA assays in 103 participants from a prostate cancer screening program in Caracas, Venezuela. We recommended biopsy to men with a total PSA level of 3 to 10 ng/mL and a free/total PSA ratio of 20% or less with either assay. We compared the sensitivity, specificity, and concordance index between the two assays to assess the effects of interassay variability on the cancer detection rate and clinical outcomes. Although the total PSA results were similar between the assays, the free PSA level was significantly greater with one assay. Therefore, the free/total PSA ratio was discordant between the two assays, resulting in different biopsy recommendations and cancer detection rates. Using a free/total PSA ratio of 20% or less as the threshold for biopsy, the differences in assay sensitivity and specificity for detecting prostate cancer are significant. Commercially available assays for PSA and its derivatives are not necessarily interchangeable, and these differences might lead to different clinical outcomes. When using free and total PSA measurements to make clinical decisions, patients and physicians should be aware of the potential standardization bias and which assay is being used.

Age‐associated increase of prostate‐specific antigen in a high level of men visiting urological clinics

To evaluate the distribution of serum prostate-specific antigen (PSA) levels as a function of age in men with no evidence of prostate cancer who visited urological clinics. Simultaneous measurements of total PSA and PSA-alpha-1-antichymotrypsin (PSA-ACT) were performed on patients who presented at urological clinics in Japan. After excluding 490 patients because of follow-up biopsy findings indicating prostate cancer, patients' history of prostatic surgery and medication affecting the serum PSA level, 1520 patients with PSA levels of less than 20.0 ng/mL were available for the study. Medians (95th percentile) of the total PSA levels were 0.9 (4.7), 1.2 (5.6), 1.7 (11.0), 2.1 (9.8) and 2.8 (11.0) ng/mL in men in their 40s (n = 37), 50s (n = 211), 60s (n = 488), 70s (n = 609) and 80s (n = 175), respectively, whereas those of PSA-ACT were 0.5 (2.9), 0.7 (3.7), 1.1 (7.4), 1.2 (5.9) and 1.6 (6.4) ng/mL, respectively. Both total PSA and PSA-ACT increase with aging, although comparison between the 10-year age groups showed a significant difference in the two molecular forms only between men in their 50s and 60s. The PSA ranges of men who visited urological clinics were higher than those of men participating in prostate cancer screening programs reported in other published studies. An age-associated increase in PSA similar to screening populations was also observed in urological outpatients. The results of the present study indicate that age-adjusted PSA cut-off levels can be used in outpatient settings, although the PSA reference value derived from the screening population should be carefully applied to symptomatic men of clinical practices.

Serum Total Prostate-Specific Antigen Assay in Women with Cushing’s Disease or Alcohol-Dependent Pseudo-Cushing’s State

Background: The distinction between Cushing’s disease (Cushing’s syndrome dependent on adrenocorticotropic hormone (ACTH)-secreting tumors of pituitary origin) and pseudo-Cushing’s states (Cushingoid features and hypercortisolism sometimes present in alcoholic, depressed or obese subjects) can present a diagnostic challenge in clinical endocrinology. Recently, the availability of a highly sensitive immunofluorometric assay for the measurement of total prostate-specific antigen (PSA) provided the possibility to measure serum PSA levels in women. Interestingly, PSA gene expression and protein production has been found to be upregulated by steroid hormones, such as androgens, glucocorticoids, mineral corticoids and progestins. In fact, serum total PSA concentrations appear to be higher in female patients with Cushing’s disease than in normal women. We wondered whether a similar phenomenon also occurs in pseudo-Cushing’s state. Methods: In order to answer this question, we compared the serum total PSA levels measured in 10 female subjects with alcohol-dependent pseudo-Cushing’s state with those observed in 8 female patients with Cushing’s disease and in 15 age-matched healthy women. Serum testosterone, ACTH and cortisol, and 24-hour urinary cortisol levels were measured; cortisol suppression after dexamethasone was also tested in all subjects. Results: The basal serum levels of ACTH and cortisol were significantly lower in normal subjects than in patients with Cushing’s disease or pseudo-Cushing’s state; these latter groups showed similar basal hormonal values. Dexamethasone administration was unable to suppress serum cortisol levels in 5 subjects with Cushing’s disease and 6 subjects with pseudo-Cushing’s state. Serum testosterone values in the group with Cushing’s disease were higher than in the other groups. No differences were observed between pseudo-Cushing’s and normal subjects. Serum total PSA levels were significantly higher in women with Cushing’s disease than in subjects with pseudo-Cushing’s state and normal controls; these latter groups showed similar PSA values. When serum total PSA and testosterone levels were considered together, a significant positive correlation was observed in the group with Cushing’s disease, but not in the other groups. Conclusions: These data indicate that the steroid milieu responsible for the elevation in serum PSA in women with Cushing’s disease is not present in subjects with alcohol-dependent pseudo-Cushing’s state, suggesting the possible use of PSA as a marker of differentiation between these pathological conditions in women.

Natural history of PSA increase with and without prostate cancer

Objectives To investigate the natural history of prostate-specific antigen (PSA) increase in men with and without prostate cancer to clarify the probability of cancer-related PSA increase. Methods Between 1986 and 2001, 504 men aged 79 years or younger with baseline PSA levels of 4.0 ng/mL or less and a PSA increase greater than 4.0 ng/mL on consecutive screening were enrolled in this study. The types of PSA increase were classified as “non-cancer-related PSA increase,” “suspicious cancer-related PSA increase,” and “cancer-related PSA increase.” The probability of a “cancer-related PSA increase” was investigated and stratified by baseline PSA levels and elapsed years until the PSA level increased to greater than 4.0 ng/mL. Results The probability of a “non-cancer-related increase,” “suspicious cancer-related PSA increase,” and “cancer-related PSA increase” was 57%, 15%, and 28%, respectively. The PSA velocity before the PSA increase was not significantly different between those with and without prostate cancer. A “non-cancer-related PSA increase” was observed in 92% of those with a PSA increase within 2 years of baseline PSA ranges of 2.0 ng/mL or less. Regardless of elapsed years until a PSA increase to greater than 4.0 ng/mL, a “suspicious cancer-related PSA increase” or “cancer-related PSA increase” was observed in almost one half of those with baseline PSA levels of 2.1 to 4.0 ng/mL. Conclusions Intensive serial observations should be recommended before undergoing biopsy for those with a PSA increase within 2 years of a baseline PSA range of 0.0 to 2.0 ng/mL. It may be difficult to distinguish between those with and without cancer using only subsequent total PSA measurements for the remaining cases, and prostate biopsy should be recommended at present.

Increased discrimination between benign prostatic hyperplasia and prostate cancer with equimolar total prostate specific antigen measurement

Although prostate specific antigen (PSA) is widely used in the discrimination of benign prostatic hyperplasia (BPH) and prostate cancer, its diagnostic value is controversial due to an appreciable false positive rate. In the present study, we compared a recently introduced assay method, equimolar PSA measurement, to non-equimolar PSA measurement and also determined the diagnostic value of percent free PSA with changing total PSA (tPSA) measurements. Between April 1999 and December 2001, the sera of 61 patients with BPH and 41 with prostate cancer were examined. Total PSA and free PSA was determined using the Immulite 2000 assay system, whereas equimolar tPSA measurement was performed using Bayer PSA Q for the Chiron ACS 180 system. Comparative analysis of the two different assays revealed better diagnostic sensitivity and specificity values for equimolar tPSA measurement, which in turn would have led to 10% of the patients avoiding an unnecessary biopsy. Additionally, percent free PSA with the changing denominator of tPSA assays showed that the free PSA/equimolar tPSA ratio was the best tumor marker among the studied forms of PSA. It was concluded that equimolar tPSA measurement using recombinant Fab fragments is superior to the classical measurements with monoclonal antibodies, and that the use of percent free PSA with the equimolarly measured tPSA has better sensitivity and specificity in the discrimination of benign and malignant diseases of the prostate.

Prostate-specific antigen levels in young white and black men 20 to 45 years old

Objectives. To determine the prostate-specific antigen (PSA) levels and PSA change over time in young white and black men 20 to 45 years old. Methods. The Department of Defense Serum Repository, a serum bank that stores all residual serum from the military human immunodeficiency virus screening program at −25°C, was sampled to obtain a total of 588 black and 588 white subjects 20 to 45 years old. This was a retrospective study with only demographic data available on the studied subjects. The samples used for this study were collected between June 24, 1988 and June 12, 1996. Individuals with a history of prostate disease were excluded by query of a centralized Department of Defense diagnosis database. Three serum specimens evenly distributed over a mean of 6 years were selected for each individual to determine the free and total PSA levels and PSA velocity. The Hybritech Tandem-E PSA assay was used for the total PSA measurement, and the Hybritech Tandem-R assay was used for the free PSA measurement. Results. The baseline serum PSA levels differed by race ( P = 0.04). The median (25th, 75th percentile) baseline serum PSA levels for black men 20 to 29, 30 to 39, and 40 to 45 were 0.38 ng/mL (0.26, 0.61), 0.45 ng/mL (0.32, 0.67), and 0.52 ng/mL (0.37, 0.73), respectively. The median baseline serum PSA levels for the same decade groups in white men were 0.38 ng/mL (0.27, 0.57), 0.45 ng/mL (0.28, 0.68), and 0.40 ng/mL (0.26, 0.64), respectively. The PSA velocity was higher in white men than in black men (mean 2.8%/yr and 1.6%/yr, respectively, P = 0.032). Conclusions. These results suggest that although black men 20 to 45 years old have higher baseline serum PSA levels than white men of the same age, the PSA velocity is greater in young white than in young black men. Additional work is needed to determine the clinical significance of these findings.

Study of free to total prostate specific antigen ratio in the detection of patients with prostate cancer

We investigated the clinical usefulness of free to total serum prostate specific antigen (PSA) ratio (F/T ratio) in order to improve the specificity of total PSA measurement for detecting prostate cancer. In this study 129 patients with total PSA level 4-20 ng/ml underwent transrectal ultrasound guided sextant biopsy. Serum samples were assessed for total PSA, free PSA and the F/T ratio calculated. All patients were pathologically diagnosed as benign prostatic hyperplasia or prostate cancer. Of 129 patients 21 had prostate carcinoma (PCa) and 108 had benign prostatic hyperplasia (BPH) from the results of prostate biopsies. The mean of total PSA were not significantly different between men with PCa and with BPH. The mean of free PSA for PCa was significantly lower than that for BPH (p = 0.043). Furthermore, the mean of F/T ratio was significantly different between PCa and BPH group (p = 0.0014). The F/T ratio had a higher specificity than total PSA at all levels of sensitivity in detecting prostate cancers. Sensitivity, specificity and accuracy for cancer detection at a cut off 0.12 was 90.4%, 51.8% and 58.1%, respectively. Also, free PSA was as useful as F/T ratio for cancer detection when analyzed in receiver operating characteristic curves analysis. When determined the cut off number of free PSA at 0.78 ng/ml, the sensitivity, specificity and accuracy for cancer detection were 61.9%, 66.7% and 65.9%, respectively. This study indicated that the F/T ratio and free PSA could improve the specificity without impairing the sensitivity for detecting PCa in patients with 4-20 ng/ml of total PSA.

New developments in the standardization of total prostate-specific antigen

Objective: Analytical evaluation of the calibration of three recently launched assays for the measurement of total prostate-specific antigen, i.e., IMx Total PSA (Abbott), Elecsys PSA (Roche), and IMMULITE 3rd Generation PSA (DPC). Design and methods: For accuracy assessment two reference materials were applied namely, Stanford 90:10 PSA Calibrator and Certified Reference Material 613 Prostate-Specific Antigen. Dilutions of these preparations were analyzed with all assays. In addition, clinical specimens from known prostate cancer or benign prostate hyperplasia patients and samples taken from an ongoing prostate cancer screening study were used for comparison. Results: Application of the Stanford Calibrator revealed results well within 10% of the calculated values for all assays. Regarding the CRM Calibrator only the IMx Total PSA proved to approach the line of identity. The IMMULITE results differed about 40% and the Elecsys about 18% from the calculated values. The comparison with clinical specimens showed statistically different results for the combination IMMULITE-IMx and for IMMULITE-Elecsys. The regression lines for both collections were: y( IMx)=0.86×( IMMULITE)+0.12 (n = 104, r = 0.970, S y/x = 0.883 μg/L) and y( Elecsys)=0.98×( IMMULITE)+0.38 ( n = 97, r = 0.976, S y/x = 0.733 μg/L). In the lower measuring range (PSA < 5.0 μg/L) as measured with the screening samples ( n = 43), these differences were less pronounced. Conclusion: In analytical sense a difference was found for both reference preparations in the assays studied. Clinically, despite improvements in methodology, results for total prostate-specific antigen are still not interchangeable. The possible consequences need to be elaborated.

Effect of the Ratio of Free to Total Prostate-specific Antigen on Interassay Variability in Proficiency Test Samples

Up to sevenfold differences were observed between total prostate-specific antigen (PSA) methods for New York State Proficiency Test samples prepared with seminal fluid PSA in human female serum. Because the PSA was mainly in its free form under these conditions, we wanted to determine whether a defined mixture of free and complexed PSA would reduce the interassay differences. We prepared a series of five solutions of 60 g/L bovine serum albumin with 10 microgram/L total PSA consisting of varied proportions of free, noncomplexible PSA, and alpha(1)-antichymotrypsin (ACT)-complexed PSA from 0% to 100%. Two hundred seventy laboratories measured the total PSA in these samples, and 16 laboratories also analyzed the samples for free PSA. The results were used to calculate free/total PSA ratios. Interassay CVs for total PSA measurements were approximately 7% at 10-15% free PSA but became gradually larger as the free/total PSA ratio increased. Measured free-PSA concentrations were similar within each sample (mean CV, 12%), and the results were relatively independent of the proportion of free PSA in the samples. Twofold discrepancies between actual and expected ratios were observed with some methods at 100% free PSA and to a lesser degree at 30% free PSA. At 100% free PSA, the relatively higher total-PSA values measured by nonequimolar methods yielded low free/total PSA ratios of 50-60%. In contrast, the lower total PSA values obtained by equimolar methods yielded ratios close to the expected 100%. Preparing proficiency test samples with a 10:90 mixture of free, noncomplexible PSA:PSA-ACT is a viable alternative to the use of seminal fluid PSA. Furthermore, the method used to measure total PSA may have a substantial impact on the calculated proportion of free PSA and hence may have clinical relevance.

Analytical Performance of Free PSA Immunoassays: Results from an Interlaboratory Survey,

Prostate-specific antigen (PSA) is a glycoprotein that is secreted by the prostate into the seminal fluid. Low concentrations of the protein are normally released into blood, but in prostate cancer (CAP) as well as in a high proportion of subjects with benign prostatic hyperplasia (BPH), serum PSA concentrations frequently increase above normal values (4 μg/L). Therefore, immunoassays measuring serum PSA concentration are routinely carried out to diagnose prostate diseases and to monitor progress of the disease and relapse of CAP after removal of the prostate (1)(2)(3). A few years ago, PSA was reported to be present in serum in three different forms. The predominant molecular form is complexed to α1-antichymotrypsin, whereas a minor fraction circulates in a free noncomplexed form. These two forms are both measured by PSA assay. Only a very small proportion of PSA circulates bound to α2-macroglobulin; this third form, however, is a nonimmunoreactive complex. The free, noncomplexed form of PSA is reported to constitute a minute proportion of the serum PSA in patients with CAP, but to be significantly greater in subjects affected by BPH. On the basis of this observation the simultaneous measurement of total PSA (tPSA) and free PSA (fPSA) has been suggested. The computed ratio fPSA/tPSA is considered a useful tool to better discriminate between BPH subjects and CAP patients and therefore to improve the early diagnosis of CAP (4). …

Assay for prostate specific antigen (PSA): problems and possible solutions.

The absolute tissue specificity of prostate specific antigen (PSA) allows the use of PSA test not only for detecting recurrence or metastasis at an early stage after radical prostatectomy but also for screening prostate cancer if combined with digital rectal examination. There is also a need to improve the current PSA test to better differentiate between prostate cancer and benign prostate hyperplasia (BPH). Because of these clinical applications, a much greater demand was placed on PSA test for extra sensitivity, accuracy, and precision even within the normal PSA concentration range. However, the current commercial assay kits for PSA do not provide correct PSA values. Many factors contributing to the problem include the specificity of the anti-PSA antibodies, the composition of the calibrator, the PSA values assigned to the calibrator, the PSA isoform used for anti-PSA antibody preparation, the test design, and the composition of the diluent. Most problems were derived from the failure of realizing earlier that the majority of the PSA exists in serum not as free PSA but as complexes with protease inhibitors. Other problems, such as constantly changing composition of various forms of PSA in serum specimens, and different clearance rates for various forms of PSA make almost impossible to develop an ideal assay for PSA. Therefore, we suggest that test should be designed for measuring PSA-ACT (PSA-alpha 1-antichymotrypsin) complex only. Changing the focus from the measurement of total PSA of various forms to the PSA-ACT complex alone may improve the differentiation between prostate cancer and BPH but may also simplify the selection of anti-PSA antibodies and the preparation of calibrator for the assay.