To normalize or not?: Dilute Russell viper venom time testing

We conducted a comparison between the nonnormalized dilute Russell viper venom time (dRVVT) screen/confirm ratio (SCR) in patient plasma and the normalized SCR obtained using reference pooled plasma. The aim was to assess the impact of normalization on the lupus anticoagulant (LA) status in our patient population.

In our retrospective analysis, we included a total of 464 patients who underwent dRVVT testing. For those with positive screens, mixing studies were performed, followed by confirmatory testing. Additionally, the dRVVT of reference pooled plasma was measured. A positive conventional (nonnormalized) or normalized SCR was defined as an SCR greater than or equal to 1.2.

In total, 5.6% (26) of the 464 samples tested were confirmed positive for LA by both methods, out of which 12 had a clinical history of thrombosis. Although a statistically significant difference between the 2 groups (P = .0096) was found, the magnitude of absolute mean SCR differences (bias) was 0.04 (2.51%). There was 100% concordance of testing results between the 2 groups.

The lupus anticoagulant status by the dRVVT assay was not changed based on normalization. Normalization was of no clinical benefit in our patient population; therefore, there was no need for the extra calculation step. Normalization may be useful for intermethod and interlaboratory studies and not for within-method LA detection.