The SGM Population Assay Kit contains all the materials required to perform accurate population assays of SGM Biotech's biological indicator products.

The kit includes:

• Detailed population assay instructions.
   
• One (1) 250ml Wheaton bottle containing 240ml growth medium.
   
• Four (4) 19.5 x 145mm sterile flat-bottom tubes with four (4) 6mm glass beads.
   
• Twelve (12) 16 x 125mm sterile dilution blank tubes.
   
• Eight (8) 1ml pipettes.
   
• Eight (8) 2ml pipettes.
   
• Two (2) 5ml pipettes.
   
• Six (6) 10ml pipettes.

Answer: Currently the USP, ISO and European Norms indicate that a population test is considered valid if the value is between minus (-) 50% and plus (+) 300% of the value stated on the certificate.

The USP has expressed this "window" in terms of "log" values. It states "The requirements of the test are met if the log average number of viable spores per carrier is not less than 0.3 log of the labeled spore count per carrier and does not exceed the log labeled spore count per carrier by 0.48.

When these values are actually calculated -0.3 log = -50% and plus 0.48 is = +300%. These values are the same for all three guidance documents.

Answer: Not according to the standards.

Rationale: The requirement to reproduce D-values to within the +/- 20% is a manufacturers specification when reproducing ones own test results. Users have erroneously adopted this guideline.

ANSI/AAMI/ISO 11138-1:2006, which replaces ANSI/AAMI ST59:1999 and EN 866:1999, states the following:

6.4.3. The D-value shall be within +/- 20% of the manufacturers stated value when determined by the manufacturer during the stated shelf life using the method specified by the manufacturer.

A study conducted in 1990 by Gordon Oxborrow1 of the FDA laboratory in Minnesota concluded that the +/- 20% specification is not appropriate for third party testing and is only likely to be routinely achieved when the manufacturer is reproducing their own data. Shintani2 et al. 2000, has also stated that if there are significant differences in spore recovery (D-values) with different lots and manufacturers of soybean casein digest media. If end users insist upon testing to the +/- 20% specification, they are likely to routinely reject good product based on misinterpretation of the standards.

1Medical Device & Diagnostic Industry, May 1990, p. 78-83, G. S. Oxborrow, C. W. Twhoy and C. A. Demitrius

2PDA Journal of Pharmaceutical Science & Technology, Vol. 54, No. 1, January/February 2000, p. 6-12, H. Shintani, K. Sasaki, Y. Kajiwara, J. Itoh, M. Takahashi, and M. Kokubo

Copyright Ati Atlas Ltd 2009