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

An ultrasensitive and disposable electrochemical aptasensor for prostate-specific antigen (PSA) detection in real serum samples

In this study, we constructed a disposable indium tin oxide polyethylene terephthalate film (ITO-PET)-based electrochemical aptasensor for analyzing prostate-specific antigen (PSA), one of the most important biomarkers of prostate cancer. Because of their clinical importance, building PSA biosensing systems with high sensitivity and stability is essential. However, it still presents significant difficulties, such as low detection limits. We designed a platform to covalently bind the amino-terminated aptamer by modifying the ITO-PET surface with carboxyethylsilanetriol (CTES) to obtain a self-assembled monolayer (SAM). We also evaluated the potential for use in real human serum samples by investigating the optimal operating conditions and analytical performance characteristics of the developed biosensor. The design we present here exhibits excellent precision, with a limit of detection (LOD) as low as 8.74 fg/mL PSA. The broad linear detection range of the biosensor under optimal conditions was determined as 1.0-1500 fg/mL. The dissociation constant (K_d) for the aptamer was also calculated as 46.28 ± 5.63 nM by evaluating the impedimetric response as a function of PSA concentration. The aptasensor displayed considerable repeatability (1.3% RSD) and reproducibility (7.51% RSD) and good storage stability (98.34% of the initial activity for 8 weeks). Additionally, we demonstrated that the technique we developed was quite efficient in estimating the kinetics of aptamer-analyte interactions by determining the K_d and single-frequency impedance (SFI) data. In conclusion, we proposed a selective and sensitive biosensor with the potential for clinical application and superior performance in real serum samples.

Verification of Harmonization of Serum Total and Free Prostate-Specific Antigen (PSA) Measurements and Implications for Medical Decisions

BACKGROUND

Previous studies have shown that the harmonization of prostate-specific antigen (PSA) assays remained limited even after the introduction of WHO International Standards. This information needs updating for current measuring systems (MS) and reevaluation according to established analytical performance specifications (APS) and the characteristics of antibodies used.

METHODS

Total (tPSA) and free (fPSA) PSA were measured in 135 and 137 native serum samples, respectively, by Abbott Alinity i, Beckman Access Dxl, Roche Cobas e801, and Siemens Atellica IM MSs. Passing-Bablok regression and difference plots were used to compare results from each MS to the all-method median values. Agreement among methods was evaluated against APS for bias derived from biological variation of the 2 measurands.

RESULTS

The median interassay CV for tPSA MSs (11.5%; 25-75th percentiles, 9.2-13.4) fulfilled the minimum APS goal for intermethod bias (15.9%), while the interassay CV for fPSA did not [20.4% (25-75th percentiles, 18.4-22.7) vs goal 17.6%]. Considering the all-method median value of each sample as reference, all tPSA MSs exhibited a mean percentage bias within the minimum goal. On the other hand, Alinity (+21.3%) and Access (-24.2%) were out of the minimum bias goal for fPSA, the disagreement explained only in minimal part by the heterogeneity of employed antibodies.

CONCLUSIONS

The harmonization among tPSA MSs is acceptable only when minimum APS are applied and necessitates further improvement. The marked disagreement among fPSA MSs questions the use of fPSA as a second-level test for biopsy referral.

Acrylamine-induced autoimmune phenomena

The objective of this study is to document a series of cases of occupationally derived autoimmune disease. Individuals with occupational exposure to acrylamides were evaluated clinically and biochemically/immunologically for evidence of autoimmune disease. Symptoms and signs and immuno-reactivity were monitored during exposure-free and re-exposure as part of the individuals' clinical evaluation. Six individuals with occupational acrylamide exposure had clinical and laboratory alterations characteristic of drug-induced autoimmune disease, specifically lupus, anti-phospholipid syndrome, Sjogren's syndrome, scleroderma, and polymyositis. The similarity of the full spectrum of disease in the reported patients to that found with procainamide strongly suggests the effects of occupational exposure. This uncontrolled study suggests the need for a full epidemiologic analysis of all individuals working with such occupational exposure, including full clinical and immunological examination.

Elevated levels of oxidized low-density lipoprotein and of catalase activity in follicular fluid of obese women

The intrafollicular levels of oxidized low-density lipoprotein (oxLDL) and of enzyme antioxidants might contribute to reproductive disorders in obese and infertile women. Relevant data are missing. Eighty-four patients were grouped according to obese versus non-obese status and whether they had polycystic ovary syndrome (PCOS). The concentrations of oxLDL and the activities of superoxide dismutase (SOD), catalase, glutathione peroxidase (GPx) and glutathione reductase (GR) in the serum and follicular fluid were measured. Obese women with and without PCOS had significantly greater amounts of oxLDL in the follicular fluid as compared with non-obese women. The level of oxLDL in the follicular fluid was 1000 times lower than in serum. Obese women with and without PCOS had significantly higher catalase activity in the follicular fluid as compared with non-obese women. No differences were found for the SOD activity in the follicular fluid. The GPx and GR activities were up-regulated in obese patients without and with PCOS, yet not in respect to each serum and follicular fluid sample. We conclude that elevated levels of oxLDL in the follicular fluid of obese women are associated with higher catalase activity; both parameters are independent of PCOS. The levels of oxLDL and catalase activity appear to indicate different degrees of oxidative stress.

Improving the comparability of immunoassays for prostate-specific antigen (PSA): Progress and problems

BACKGROUND

Commutability of immunoassay test results is an important objective for laboratory medicine.

METHODS

PSA is a clinically important analyte for which, as a consequence of a number of national and international initiatives over the last decade, considerable progress has been made towards improving method comparability. However, results from different assays are still not interchangeable, a situation that is only likely to improve once broad recommendations can be made about the most clinically relevant antibody combinations.

CONCLUSIONS

Universal implementation of such recommendations would almost certainly improve between-method agreement substantially, provided careful attention were paid to assay design and use of appropriately pure secondary standards ensured.

Comparison of 6 automated assays for total and free prostate-specific antigen with special reference to their reactivity toward the WHO 96/670 reference preparation

BACKGROUND

Prostate-specific antigen (PSA) assays have historically produced different results. Our aim was to investigate the comparability of assay results of selected commercially available assay methods designed to measure total, free, or complexed PSA (tPSA, fPSA, and cPSA).

METHODS

We measured tPSA, fPSA, and cPSA in 70 samples and in the WHO PSA 96/670 reference preparation with 6 assays (Beckman-Coulter Access, Abbott ARCHITECT and AxSYM, Bayer Advia Centaur, DPC IMMULITE 2000, and Roche Modular Analytics E170). We also calculated the fPSA/tPSA ratio.

RESULTS

The mean deviations from the expected tPSA and fPSA values for the WHO 96/670 reference preparation were 0.37 (range, 0.01-1.32) and 0.19 (range, 0.05-0.49) microg/L, respectively. When plotted against the expected WHO 96/670 reference preparation value, regression slopes varied from 0.99 to 1.22 and r2 from 0.9996 to 1.000. When total PSA was measured in mixtures of sera with high and low tPSA concentrations, the mean (SD) slope of regression of different assays against an in-house method was 1.04 (0.09). In these specimens, the fPSA/tPSA ratio was 0.11-0.14 with different methods. The tPSA and fPSA values in patient samples measured in different assays and plotted against ARCHITECT gave regression slopes from 0.88 to 0.97. The results of the studied assays for tPSA in serum samples agreed within 15%, from each other, and all results for the WHO 96/670 reference preparation were within 6.8% (confidence interval, 1.7%-15.2%) of the expected value. The results for fPSA were more diverse.

CONCLUSIONS

Differences among PSA assays appear to have decreased since introduction of the WHO 96/670 reference preparation, but further efforts are needed to harmonize fPSA assays.