A significantly lower potency observed for the 3rd WHO International Standard for Parvovirus B19V DNA with the cobas TaqScreen DPX test

Background In the context of the Official Medicines Control Laboratories plasma pool testing for Parvovirus B19 DNA, we use the cobas TaqScreen DPX test. When we re‐evaluated this method using the 3rd B19 DNA WHO IS at the final concentration of 4 log IU/mL, we observed a titre lower than expected, i.e. 3.79 log IU/mL. Therefore, we further investigated the accuracy of the DPX test. Materials & Methods The following B19V DNA materials were tested by using both the DPX test and an in‐house real‐time PCR: The 1st, 2nd and 3rd WHO ISs for B19V DNA The Non WHO B19V DNA Reference Material for NAT The Biological Reference Preparation B19 virus DNA for NAT testing, batch 1 . Results The DPX test showed a good accuracy for all B19V DNA materials with the exception of the 3rd WHO IS for B19V DNA. In fact, an underestimation of about 38% was observed for all dilutions of this standard with respect to the nominal titre. With the B19V in‐house real‐time PCR, all four materials proved to be well calibrated against the 1 st WHO IS for B19V DNA, used as external standard curve. Conclusion In this study, we demonstrated that the DPX test underestimates the B19V DNA content of the 3rd WHO IS for B19V DNA and that this is not due to an incorrect potency assigned to the standard but, most probably, to a mismatch between the primers/probe and the sequence of the target region in the 3rd WHO IS for B19V DNA.