Interlaboratory Quality Control Program Research Articles

International circumpolar surveillance: update on the interlaboratory quality control program for Streptococcus pneumoniae, 2009 to 2020.

Arctic populations experience several social and physical challenges that lead to the increased spread and incidence of invasive diseases. The International Circumpolar Surveillance (ICS) program was developed to monitor five invasive bacterial diseases in Arctic countries and territories. Each ICS organism has a corresponding interlaboratory quality control (QC) program for laboratory-based typing, to ensure the technical precision and accuracy of reference testing services for these regions, and identify and correct potential problems. Here, we describe the results of the ICS Streptococcus pneumoniae QC program, from 2009 to 2020. Excellent overall concordance was achieved for serotype and antimicrobial susceptibility testing results across six laboratories. Ongoing participation in these QC programs ensures the continuation of quality surveillance systems within Arctic populations that experience health disparities.

Ten-year results of an international external quality control programme for measurement of anti-tuberculosis drug concentrations.

Participation in an external (interlaboratory) quality control (QC) programme is an essential part of quality assurance as it provides laboratories with valuable insights into their analytical performance. We describe the 10 year results of an international QC programme for the measurement of anti-tuberculosis (TB) drugs. Each year, two rounds were organized in which serum (or plasma) samples, spiked with known concentrations of anti-TB drugs, were provided to participating laboratories for analysis. Reported measurements within 80%-120% of weighed-in concentrations were considered accurate. Mixed model linear regression was performed to assess the effect of the measured drug, concentration level, analytical technique and performing laboratory on the absolute inaccuracy. By 2022, 31 laboratories had participated in the QC programme and 13 anti-TB drugs and metabolites were included. In total 1407 measurements were reported. First-line TB drugs (isoniazid, rifampicin, pyrazinamide and ethambutol) represented 58% of all measurements. Overall, 83.2% of 1407 measurements were accurate, and the median absolute inaccuracy was 7.3% (IQR, 3.3%-15.1%). The absolute inaccuracy was related to the measured anti-TB drug and to the performing laboratory, but not to the concentration level or to the analytical technique used. The median absolute inaccuracies of rifampicin and isoniazid were relatively high (10.2% and 10.9%, respectively). The 10 year results of this external QC programme illustrate the need for continuous external QC for the measurement of anti-TB drugs for research and patient care purposes, because one in six measurements was inaccurate. Participation in the programme alerts laboratories to previously undetected analytical problems.

Evaluation of the Bio-Evolution Microsporidia generic and typing real-time PCR assays for the diagnosis of intestinal microsporidiosis.

Cases of intestinal microsporidiosis infection are underestimated and affect both immunocompromized and immunocompetent patients. Real-time PCR is superseding microscopic examination for its diagnosis in medical analysis laboratories. However, few manufacturers include microsporidia in their PCR panel for the diagnosis of infectious gastroenteritis. Here, we evaluated the performances of the real-time PCR assays microsporidia generic and microsporidia typing (Bio-Evolution, France) on the Rotor-Gene Q real-time PCR cycler (Qiagen, France). We included 45 negative and 44 positive stool samples for Enterocytozoon bieneusi (n=34, with various genotypes), Encephalitozoon intestinalis (n=4), Encephalitozoon hellem (n=4), and Encephalitozoon cuniculi (n=2). We also studied a four-year survey of an inter-laboratory quality control program including 9 centers that used this commercial assay. Sensitivity and specificity of the microsporidia generic assay were 86.4% and 93.3%, respectively. Encephalitozoon hellem and Encephalitozoon cuniculi were detected by the microsporidia generic PCR assay but not by the microsporidia typing PCR assay. These results were consistent with the results of the inter-laboratory quality control program. In conclusion, Bio-Evolution Real-time PCR assays are useful tools for intestinal microsporidiosis, but negative results for microsporidia typing assays require supplementary analyses to confirm E. hellem or E. cuniculi infections.

International circumpolar surveillance interlaboratory quality control program for emm typing of Streptococcus pyogenes, 2011–2015

In 2011, an interlaboratory quality control (QC) program for emm typing group A streptococci (GAS) was incorporated into existing international circumpolar surveillance QC programs. From 2011 – 2015, 35 GAS isolates were distributed to three laboratories; emm type-level concordance was 100%, while the overall sub-type level concordance was 83%.

Monitoring invasive bacterial diseases in the North American Arctic via the International Circumpolar Surveillance Project.

This paper summarizes the most recent Invasive Bacterial Diseases (IBD) Working Group meeting of the International Circumpolar Surveillance (ICS) project. The ICS is a population-based surveillance network for invasive bacterial diseases that provides a mechanism to determine changes in incidence rates and antimicrobial resistance. The meeting took place in Montreal, Canada on February 12-13, 2014. Data were included from participating Canadian provincial and territorial jurisdictions as well as from the State of Alaska. This report is based on the audio records of the meeting as well as the meeting presentations. The ICS IBD Working Group focuses on invasive diseases caused by: Streptococcus pneumoniae (Sp), Neisseria meningitidis (Nm), Haemophilus influenzae (Hi), Group A Streptococcus (GAS) and Group B Streptococcus (GBS). Data on invasive disease caused by each of these organisms were reviewed through December 2012-2013. Although the incidence of some of these vaccine-preventable invasive diseases has decreased, emergence of H. influenzae serotype a (Hia) in both Alaska and Northern Canada was noted. An interlaboratory quality control (QC) program is ongoing to monitor laboratory proficiencies for serotyping.

Poor performance of laboratories assaying newly developed antiretroviral agents: results for darunavir, etravirine, and raltegravir from the international quality control program for therapeutic drug monitoring of antiretroviral drugs in human plasma/serum.

The International Interlaboratory Quality Control PROGRAM for Therapeutic Drug Monitoring of Antiretroviral Drugs in Human Plasma/Serum was initiated in 1999. We have previously published our experience during the first 10 years of the PROGRAM. Since 2010, 3 newly developed antiretroviral agents have been added to the darunavir, etravirine, and raltegravir. The objective of this analysis is to describe the performance of participating laboratories measuring these newer agents in 2011-2012. Each year, laboratories received 2 blind samples of human plasma/serum spiked with a low (<1.0 mg/L), medium (1.0-5.0 mg/L), or high (>5.0 mg/L) concentration of these drugs. Laboratory results were standardized to percentages with reference to the nominal (true) concentration. Any result that deviated more than 20% of the nominal values was defined as inaccurate. The numbers of laboratories that participated by the end of 2012 were 44 for darunavir, 28 for etravirine, and 30 for raltegravir. A total of 357 results were evaluable for analysis. Of these, 64 (17.9%) results were reported with >20% deviation, so "inaccurate" (7.6% too low, 10.4% too high). The proportion of inaccurate results in 2011 was 21.3% for darunavir, 31.0% for etravirine, and 26.3% for raltegravir; in 2012, these figures improved to 8.1%, 23.2%, and 8.3% for darunavir, etravirine, and raltegravir, respectively. Taking darunavir as the reference, performance for etravirine was significantly lower [odds ratio = 0.462, 95% confidence interval: 0.246-0.866, P = 0.016] and performance for raltegravir was not significantly different. Low concentrations were significantly more frequently reported as inaccurate than medium or high concentrations: 28.6% versus 10.6% versus 8.8%, respectively (P < 0.001). Laboratories that used Liquid Chromatography with tandem Mass Spectrometry did not perform better than those using High Performance Liquid Chromatography/Ultrarapid Performance Liquid Chromatography: 41 inaccurate results in 200 samples (20.5%) versus 23 in 157 samples (14.6%, P = 0.154). Multiple logistic regression revealed that the concentration range was the only significant predictor of inaccurate results. The lower range of concentrations performed worse than medium or high concentrations (P < 0.001). Laboratories continue to have problems with adequately measuring low plasma concentrations of antiretroviral agents. This is particularly a problem for some of the newer antiretroviral agents with plasma concentrations in the <1.0 mg/L range, such as etravirine and raltegravir.

Darunavir and telaprevir drug interaction: total and unbound plasma concentrations in HIV/HCV-coinfected patients with cirrhosis

Sir, Telaprevir is an NS3/4A protease inhibitor approved for the treatment of chronic hepatitis C virus (HCV) genotype 1. Telaprevir is primarily metabolized by cytochrome 450 3A4 (CYP3A4). Also, telaprevir is a potent inhibitor of CYP3A4 and intestinal P-glycoprotein, resulting in increased concentrations of CYP3A substrates. Darunavir is mainly metabolized by CYP450 and ritonavir is a potent CYP450 inhibitor. Significant drug–drug interactions have been described in healthy volunteers between telaprevir (750 mg/8 h) and darunavir/ritonavir (600/100 mg/12 h), resulting in decreases in plasma concentrations of both drugs (darunavir: Cmax1⁄4240%, AUC1⁄4240% and Cmin1⁄4242%; telaprevir: Cmax1⁄4236%, AUC1⁄4235% and Cmin1⁄4232%). Based on these data, co-administration of darunavir/ritonavir and telaprevir is not recommended. However, a darunavir/ ritonavir-based antiretroviral regimen might be necessary in treatment-experienced patients. Given that telaprevir is not a CYP3A4 inducer, other mechanistic explanations for reduced darunavir concentrations, such as protein displacement, have to be considered. Consequently, it is important to measure both total and unbound darunavir and telaprevir concentrations. Clinical and pharmacokinetic (PK) data from two HIV/ HCV-coinfected patients receiving 800/100 mg of darunavir/ ritonavir once daily and 750 mg of telaprevir/8 h are reported. Steady-state 12 h (for darunavir) and 8 h (for telaprevir) PK studies were performed before and 4 weeks after starting telaprevir. Drugs were given with a standard breakfast (550 kcal) and telaprevir was given again with food (900 kcal) after 8 h. Blood samples were drawn pre-dose (fasting) and 1, 2, 3, 4, 6, 8 and 12 h post-dose. C24 was extrapolated from C0 for darunavir. Darunavir and telaprevir total and unbound concentrations were determined by liquid chromatography–tandem mass spectrometry; unbound fractions were obtained by ultrafiltration. Area under the concentration curve (AUC) and drug clearance (CL/F) were assessed by a non-compartmental model and linear/log trapezoidal rule with WinNonlin. Our laboratory takes part in an external interlaboratory quality control programme for measurement of antiretroviral drugs in plasma by the Association for Quality Assessment in Therapeutic Drug Monitoring and Clinical Toxicology, The Hague, The Netherlands. The study of PK parameters in HIV/HCV-coinfected patients was approved by the ethics committee. Signed written consent was obtained from the patients, who consented to publication of the results.

International circumpolar surveillance interlaboratory quality control program for serotyping Haemophilus influenzae and serogrouping Neisseria meningitidis, 2005 to 2009.

The International Circumpolar Surveillance (ICS) program was initiated in 1999 to conduct population-based surveillance for invasive pneumococcal disease in select regions of the Arctic. The program was expanded to include the surveillance of invasive diseases caused by Neisseria meningitidis and Haemophilus influenzae. An interlaboratory quality control (QC) program to monitor laboratory proficiencies in the serogrouping of N. meningitidis and serotyping of H. influenzae strains was codeveloped by the Arctic Investigations Program (Anchorage, AK) and the Public Health Agency of Canada National Microbiology Laboratory (Winnipeg, Manitoba, Canada) and introduced into the ICS program in 2005. Other participating laboratories included the Provincial Laboratory for Public Health (Edmonton, Alberta, Canada), Laboratoire Santé Publique du Québec (Sainte-Anne-de-Bellevue, Québec, Canada), and Statens Serum Institut (Copenhagen, Denmark). From 2005 through 2009, 50 isolates (24 N. meningitidis and 26 H. influenzae isolates) were distributed among the five participating laboratories. The overall serogroup concordance for N. meningitidis strains was 92.3% (96/104), without including three isolates that were found to express both serogroup Y and W135 specificities. Concordant results were obtained for serogroups A, B, C, and Y among all laboratories. Discrepancies were observed most frequently for serogroups W135, X, Z, and 29E. The overall serotype concordance for H. influenzae was 98% (125/127 attempts). The two discrepant results involved a serotype c strain and a serotype e strain, and in both cases, the serotypeable H. influenzae isolates were misidentified as being nontypeable. These data demonstrate a high degree of concordance for serogroup and serotype determinations of N. meningitidis and H. influenzae isolates, respectively, among the five laboratories participating in this quality control program.

The International Interlaboratory Quality Control Program for Measurement of Antiretroviral Drugs in Plasma: A Global Proficiency Testing Program

The International Interlaboratory Quality Control Program for Measurement of Antiretroviral Drugs in Plasma was initiated in 1999 by Radboud University Nijmegen Medical Center, The Netherlands, and continued later on in collaboration with the Dutch Association for Quality Assessment in Therapeutic Drug Monitoring and Clinical Toxicology (www.kkgt.nl). The aim of this analysis was to evaluate the first 10 years of the Program and to determine variables associated with reporting of less accurate results. Two rounds are organized annually in which blind samples are shipped to participants containing a low, medium, or high concentration of each antiretroviral drug. Any reported result that deviates more than 20% from the spiked concentration is defined as inaccurate. By the end of 2009, the number of laboratories participating in the Program had increased to 56; 44 (79%) are located in Europe. A total of 12,798 test results was available for analysis, of which 2104 (16.4%) were reported as inaccurate. Performance was best for samples containing nevirapine (mean of inadequate scores per round: 11.1%) and lopinavir (11.9%) and worst for indinavir (18.7%), atazanavir (18.9%), saquinavir (19.6%), and nelfinavir (21.3%). High and medium concentrations were less frequently reported as inaccurate than low concentrations: 13.5%, 13.0%, and 22.4%, respectively. Although the overall performance of the laboratories varied per year, a trend was visible for improvement over time with 19.9% of the results being inaccurate in 2002 (n = 20 laboratories) to 15.7% in 2009 (n = 56 laboratories). The Program provides a proficiency testing program in which laboratories are alerted to potential analytical errors while performing therapeutic drug monitoring in HIV-infected patients. Laboratories should put more effort in adequately analyzing concentrations of antiretroviral drugs with low minimum effective concentrations.

The International Circumpolar Surveillance Interlaboratory Quality Control Program for Streptococcus pneumoniae , 1999 to 2008

The International Circumpolar Surveillance (ICS) Program was initiated in 1999 to conduct population-based surveillance for invasive pneumococcal disease in select regions of the Arctic. An interlaboratory quality control (QC) program for pneumococcal serotyping and antibiotic susceptibility testing was incorporated into ICS by reference laboratories in northern Canada (Laboratoire de Santé Publique du Québec [LSPQ] in Sainte-Anne de Bellevue, Québec; National Centre for Streptococcus [NCS] in Edmonton, Alberta) and Alaska (Arctic Investigations Program [AIP]). The World Health Organization's Collaborating Centre for Reference and Research on Pneumococci at the Statens Serum Institute (SSI) in Copenhagen, Denmark, joined the QC program in 2004. The Iceland Reference Laboratory (IRL) in Reykjavik, Iceland, joined the QC program in 2006, but due to small sample sizes, data from IRL are not included in this report. From 1999 through 2008, 190 isolates were distributed among four laboratories (AIP, NCS, LSPQ, and SSI). The overall serotype concordance was 95.8%, and the overall serogroup concordance was 97.4%. The overall modal MIC concordance for testing by broth microdilution (BMD) and agar dilution was >96% for all the antibiotics except erythromycin (92.1%) and clindamycin (89.5%). MIC comparisons between the Etest and BMD resulted in lower concordance for erythromycin (73.9%), clindamycin (65.5%), and trimethoprim-sulfamethoxazole (80%); however, categorical concordance (susceptible, resistant) remained high at 98.6%, 89.1%, and 90.9%, respectively. Our data demonstrate a high degree of correlation of serotyping and antimicrobial susceptibility testing results between four participating laboratories.

Variations observed for insulin concentrations in an interlaboratory quality control program may be due to interferences between reagents and the matrix of the control materials

The present study was carried out to observe the behaviour of insulin concentrations in an interlaboratory quality control program from BioRad Laboratories (Irving, CA) applied to Immulite 2000 (Diagnostics Product Corporation, Los Angeles, CA) for three control materials of Lyphocheck Immunoassay Plus Control. Insulin was measured for 261 consecutive working days in a year using a solid-phase immunometric chemiluminescent assay; likewise insulin was measured for 55 days during a period of 4 months in a pool of sera obtained from patients with insulin concentrations within the normal range of our laboratory. The results from each control material were classified in three groups according to the closeness among concentrations and time; mean concentrations were significantly different between consecutive groups for the three control materials ( p < 0.0001). However, no differences were observed in samples from pool sera. The variations observed in insulin concentrations of the control materials may be due to some interferences or matrix effect on the control material caused by the reagents to quantify insulin in the Immulite 2000.

Reproducibility of HPV DNA Testing by Hybrid Capture 2 in a Screening Setting

Within a large Italian randomized trial on new technologies for cervical cancer screening involving 7 laboratories with different levels of experience, an intralaboratory and interlaboratory quality control program for human papillomavirus (HPV) DNA testing by Hybrid Capture 2 (HC2; Digene, Gaithersburg, MD) was implemented. To monitor the hybridization and detection steps, target samples containing purified, concentration-defined, HPV DNA were introduced in each test run. Only 3 of 1,024 showed a mistake in a positive vs negative classification with a 1 relative light unit (RLU)/positive control specimen (PC) ratio cutoff. To monitor the preanalytic steps (particularly denaturation), blinded specimens (33 collected in PreservCyt (Cytyc, Boxborough, MA) and 36 in Specimen Transport Medium (STM, Digene) were centrally prepared, divided into aliquots, and sent to each laboratory. The multiple-rater scores for negative (<1 RLU/PC), low-positive (1 to <11 RLU/PC), and high-positive (> or =11 RLU/PC) samples, respectively, were 0.91, 0.60, and 0.69 with PreservCyt and 0.93, 0.87, and 0.90 with STM. Our data showed high reliability and reproducibility with HC2, with values higher for STM than ThinPrep (Cytyc) samples.

Reproducibility of HPV DNA Testing by Hybrid Capture 2 in a Screening Setting

Within a large Italian randomized trial on new technologies for cervical cancer screening involving 7 laboratories with different levels of experience, an intralaboratory and interlaboratory quality control program for human papillomavirus (HPV) DNA testing by Hybrid Capture 2 (HC2; Digene, Gaithersburg, MD) was implemented. To monitor the hybridization and detection steps, target samples containing purified, concentration-defined, HPV DNA were introduced in each test run. Only 3 of 1,024 showed a mistake in a positive vs negative classification with a 1 relative light unit (RLU)/positive control specimen (PC) ratio cutoff. To monitor the preanalytic steps (particularly denaturation), blinded specimens (33 collected in PreservCyt [Cytyc, Boxborough, MA] and 36 in Specimen Transport Medium [STM, Digene]) were centrally prepared, divided into aliquots, and sent to each laboratory. The multiple-rater κ scores for negative (<1 RLU/PC), low-positive (1 to <11 RLU/PC), and high-positive (≥11 RLU/PC) samples, respectively, were 0.91, 0.60, and 0.69 with PreservCyt and 0.93, 0.87, and 0.90 with STM. Our data showed high reliability and reproducibility with HC2, with κ values higher for STM than ThinPrep (Cytyc) samples.

TDM: Therapeutic Drug Measuring or Therapeutic Drug Monitoring?

The third round of the International Interlaboratory Quality Control Program for Therapeutic Drug Monitoring in HIV infection (QC-program) consisted of the analysis not only of plasma samples but also of patient cases. The case was composed of different topics related to the therapeutic drug monitoring of antiretroviral drugs. The participants were asked to give recommendations concerning dose adjustments, changes to the regimen, and drug-drug interactions to observe whether the expert recommendations were comparable. Of the 30 participants of the QC-program, 16 returned their comments and recommendations with regard to the patient case. The drug level was easy to judge: approximately 90% were able to correctly do so. Almost half of the recommendations (44%) given were satisfactory. Levels of knowledge regarding HIV treatment appeared to be variable among the respondents and for this reason were partly incomparable.

International interlaboratory quality control program for measurement of antiretroviral drugs in plasma.

An international interlaboratory quality control program for measurement of antiretroviral drugs was initiated. The first round was confined to protease inhibitors and showed large variability in the performance of participating laboratories. The results demonstrate the need for and utility of an ongoing quality control program in this area of bioanalysis.

Lead contamination in Uruguay.

Uruguay is a developing country of South America with about 3 million people, half of whom live in its principal city, Montevideo. This city has several lead pollution sources as emitting industries, most of them surrounded by residential neighborhoods, some still using lead pipes in drinking water systems of old buildings, and has areas of heavy traffic with cars that are still fueled with leaded gasoline. The toxic effects of this heavy metal are well known. Children are a very sensitive population and their early symptoms of intoxication are not always taken into account. Blood lead is a good indicator of recent exposure to lead influenced by inhalation and ingestion. The systematic data assessment of lead pollution and people exposure in Uruguay was not well known when the Department of Toxicology and Environmental Hygiene of the Faculty of Chemistry began to analyze lead in biological samples, first from exposed workers and next from children and the general population, including sensitive animal species like dogs. Several described studies were carried out analyzing for blood lead to assess lead uptake and to obtain reference values for Uruguayan populations. Since 1986, that Department is the only laboratory where blood lead analyses are done, and the analytical method has been controlled by an interlaboratory quality control program of the Ministry of Labour of Spain and confirmed by experts from the Laboratory of Occupational and Environmental Medicine of Lund, Sweden. Financial and technical support was obtained from Sweden (SAREC) and also from the University of the Republic of Uruguay. Uruguayan lead workers have always been the principally studied population because their lead exposure assessment as well as their health protection education is not always done properly. Uruguay has adopted ACGIH reference values (150 micrograms/m3 in total lead dust, 50 micrograms/m3 respirable lead dust, 300 micrograms/L blood), and the high blood lead levels indicate significant adverse health risks effects and show a lack adequate controls for working conditions. A surveillance of children living in the surroundings of lead processing factories and in different neighborhoods was conducted because no data were available for blood lead in children before 1992. Also, general populations living in those areas or in areas of heavy traffic were assessed. Blood lead levels were always compared with those of control populations sampled at the same time answering a questionnaire. Workplace influence as well as atmospheric, soil, and water pollution were always considered to explain the obtained results. Some studies were carried out in dogs as a sensitive population, showing their higher exposure. The described studies included internal and external quality controls for the analytical methods and data processing. All blood lead analyses were done by atomic absorption spectrometry (AAS) after adding complexing agent and extraction. Samples taken together with Swedish researchers were analyzed in Lund (Department of Occupational and Environmental Medicine University Hospital), at 283.3 nm after electrothermal atomization (ETA). There was good correlation (r = 0.96) among 28 samples shared between Montevideo and Lund laboratories. The authors recommend more systematic clinical examination of workers, children, and the general population to determine the potential health risks for Uruguayan populations so as to improve their health conditions and to officially recognize lead pollution as an environmental problem.

National versus international asbestos fibre counting schemes: Comparison between the Spanish interlaboratory quality control programme (PICC-FA) and the asbestos fibre regular informal counting arrangement (AFRICA)

An interchange of eight asbestos reference slides was planned informally between the Spanish national proficiency testing scheme, PICC-FA, and its international counterpart, AFRICA. The fibre counting levels, the reference values and the differences in performance assessments for individual counts and laboratories were analysed to test the level of agreement between the schemes. Comparisons were based on the proportions of fibre counts within and outside limit values. Discrepancies were found between schemes in the classification of counts, with the position of the limits of satisfactory performance being the most important factor of disagreement. The AFRICA limits are over twice as wide as the PICC-FA limits, though only 17% of the counts are affected by this large difference. There were not found to be significant differences in the assessment of the performances of Spanish laboratories—87.5% would have achieved a satisfactory classification in both schemes. A possible new approach to harmonizing proficiency testing schemes is discussed.

National versus International Asbestos Fibre Counting Schemes: Comparison between the Spanish Interlaboratory Quality Control Programme (PICC-FA) and the Asbestos Fibre Regular Informal Counting Arrangement (AFRICA)

An interchange of eight asbestos reference slides was planned informally between the Spanish national proficiency testing scheme, PICC-FA, and its international counterpart, AFRICA. The fibre counting levels, the reference values and the differences in performance assessments for individual counts and laboratories were analysed to test the level of agreement between the schemes. Comparisons were based on the proportions of fibre counts within and outside limit values. Discrepancies were found between schemes in the classification of counts, with the position of the limits of satisfactory performance being the most important factor of disagreement. The AFRICA limits are over twice as wide as the PICC-FA limits, though only 17% of the counts are affected by this large difference. There were not found to be significant differences in the assessment of the performances of Spanish laboratories—87.5% would have achieved a satisfactory classification in both schemes. A possible new approach to harmonizing proficiency testing schemes is discussed. © 1998 British Occupational Hygiene Society. Published by Elsevier Science Ltd.

Cathepsin D versus other prognostic factors in breast cancer. Results and controversies of a multicenter study on 2575 cases.

The aim of this study was the survey of cathepsin D determination in a large group of patients enrolled at several centers, under the coordination of the Italian Committee for Quality Control in the Oncological Laboratory. Cathepsin D was measured with the same methodology, under control of an intra and interlaboratory quality control program, in order to verify the comparability of cathepsin D results from different institutions and to analyze the frequency of cathepsin D positive cases in subgroups of patients stratified according to other prognostic parameters. This retrospective study included 2575 patients with primary breast cancer evaluated in 10 institutions. Cytosol from tumor tissue was the substrate for biochemical cathepsin D, estrogen receptor and progesterone receptor determination, with an interlaboratory quality control survey provided by the E.O.R.T.C. Receptor Group and the Italian Committee for Quality Control in the Oncological Laboratory. The results of the present study can be summarized as follows: 1) Cathepsin D is independent of menopausal status; 2) In spite of standardization of tissue handling and assay methods, different results may be obtained by different institutions. It is therefore essential that each laboratory calculates its own positive/negative cutoff values prior to any routine clinical use of the parameter. This should be a serious consideration when a multicenter study is planned.

Quality control for evaluation of the S‐phase fraction by flow cytometry: A multicentric study

Flow cytometric measurement of the S-phase fraction (FCM-S) may be clinically useful in human cancers to identify high-risk patients. However, its clinical application requires a methodologic standardization, a high feasibility, and the reproducibility of results within the same and among different institutions. The interlaboratory quality control program for FCM-S determination (promoted by the Italian Society of Basic and Applied Cell Kinetics) was carried out on DNA diploid and aneuploid cell lines and human breast cancers. FCM-S was quantified by using four mathematical models characterized by different rationales and differences in the degree and shape of background subtraction functions. A satisfactory agreement in FCM-S values among different institutions was observed for cell lines. In human breast cancers, a high reproducibility of FCM-S estimates obtained by the different institutions was observed by using the same model. Conversely, different models gave different FCM-S estimates. Intermodel differences were more evident in aneuploid than in diploid tumors. These findings could explain the contrasting results on the prognostic role of FCM-S in clinically comparable series of breast cancers and should be considered in future efforts to define the optimal and most reproducible mathematical approach to quantify cells in the S-phase.