There are two different calibration standards for PSA tests, one from Hybritech and a more recent one from the WHO. The values for total PSA are in pretty good agreement, with some differences for free PSA. For those interested:Comparison of Three Assays for Total and Free PSA Using Hybritech and WHO Calibrations
(2021, Full Text)
: Lack of interchangeability between prostate-specific antigen (PSA) assays could have a clinical impact. We compared PSA assays from different manufacturers and calibrations.Patients and methods
: A total of 233 men who underwent prostate biopsy (PSA: 2-10 ng/ml; Beckman Coulter Access® Hybritech® as reference) were enrolled. Total (tPSA) and free PSA (fPSA) were also measured using the Roche cobas® and the Abbott Architect® methods.Results
: Roche tPSA values were ≈1% higher than Beckman, while Abbott values were ≈5% lower. Roche had the highest diagnostic sensitivity (92%) compared to Beckman Coulter (87%) and Abbott (85%). Roche fPSA was ≈3% lower and Abbott ≈17% higher than that of Beckman. For the percentage of fPSA, Roche had the highest sensitivity (98%).Conclusion
: Roche cobas® and Beckman Coulter Access® Hybritech® tPSA were almost interchangeable. While the agreement was acceptable for tPSA, this did not happen with fPSA and greater efforts for harmonization are required."From the Full Text:
"We believe that one of the main strengths of this study, is that it shows that the use of WHO-calibrated PSAs does not necessarily imply lowering the usual cut-off for recommending a prostate biopsy. Other authors had previously suggested that the usual cutoff of 4 ng/ml should be reduced to 3.1 ng/ml when PSA is measured with WHO-calibrated assays (14). Our study shows that this does not hold true for all WHO-calibrated PSA assays, namely the Roche cobas® and the Abbott Architect® assays. However, and according to studies comparing WHO- and Hybritech-calibrated PSA assays from Beckman Coulter, the observed difference of 20-25% between them could justify reducing the cut-off when using WHO-calibrated PSA from Beckman Coulter (14, 15). In fact, a limitation of this study is that the Beckman Coulter WHO-calibrated PSA assays were not evaluated.
In summary, despite the different calibrations (WHO versus Hybritech), within the 2-10 ng/ml PSA range, there is an acceptable agreement between the three manufacturers in terms of the tPSA assays, especially between Beckman Coulter and Roche, making these two tPSA methods almost interchangeable. For fPSA assays, the differences between methods are more significant, meaning that further harmonization efforts are required. The results of %fPSA showed high differences between methods, with an impact on their clinical performance. Roche cobas® tPSA and fPSA assays were more aligned with the Beckman Coulter Access® Hybritech® assays than the Abbott Architect® assays. When considering the commonly used cutoffs of 4 ng/ml and 25%, respectively, the Roche cobas® tPSA and %fPSA results had the best diagnostic performance of the three evaluated methods, with higher sensitivities, higher NPVs, and lower numbers of missed PCa."
As Forum members often advise, the ideal situation is to monitor your PSA with the exact same PSA test, if possible drawn at the same
location. Any unexpected rise in your PSA merits a retest after some interval to check for lab errors, which do happen, as do occasional "outlier" values for whatever reason.
Post Edited (DjinTonic) : 4/30/2022 9:17:12 AM (GMT-6)