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WHO/BS/2011.2161 ENGLISH ONLY
EXPERT COMMITTEE ON BIOLOGICAL STANDARDIZATION Geneva, 17 to 21 October 2011
WHO International Standards /Reference Reagents
Submission to ECBS of post-establishment stability monitoring/stability evaluation
1
stIS Prostate specific antigen (free) and 1
stIS Prostate specific antigen (90:10)
Dr. C. Burns
National Institute for Biological Standards and Control (NIBSC), Blanche Lane, South Mimms, Potters Bar, Herts, EN6 3QG, UK
© World Health Organization 2011
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Codes: PSA (free) - 96/668; PSA (90:10)- 96/670
WHO/BS/2011.2161 Page 2
Project leader C Burns
Date of evaluation May 2011
Date of establishment 1999
Principle application(s) Used for the calibration of diagnostic immunoassays for PSA.
Summary of Stability data obtained at establishment
PSA (free) A predicted degradation rate of 0.042% per year was estimated for samples stored at -20°C.
PSA (90:10) A predicted degradation rate (6) of 0.027%
per year was estimated for samples stored at -20°C.
ECBS notes/follow-up recommendations at establishment
Prostate-specific antigen standards were recommended for ongoing stability monitoring programme as they are filled in vials.
Summary of post establishment stability evaluation
Since there were no frozen baselines available for these International Standards, a second accelerated degradation study was performed.
At 12 years post-fill, ampouled materials (stored at elevated temperatures for 13 months) were compared with ampoules stored at -20 degrees C. See Table A below.
A lack of degradation at +4 and +20 precludes a prediction of degradation rate using the Arrhenius equation but supports the predictions on stability made at
establishment.
Recommendation for ECBS endorsement
ECBS is asked to note that these current stability studies have confirmed predictions at time of establishment Proposed date of further
evaluation
The remaining stocks of these standards are low and are predicted to last no more than 4-5 years. As a result, no further stability assessment is proposed.
Table A
Potency1 (with 95% confidence limits) relative to -20°C sample Storage temperature
96/668 96/670
+4°C 1.05 (0.97 – 1.14) 0.99 (0.93 – 1.06) +20°C 1.02 (0.94 – 1.10) 1.04 (0.97 – 1.11) +37°C 0.87 (0.80 – 0.94) 0.90 (0.84 – 0.96)
1All potencies are weighted geometric mean estimates from two assays.
= = =
