A new note from Sheila Minor: Hi George! Thank you for responding to my question in regard to using an intermediate sensitivity PTT reagent for general screening and heparin management and a LAC-sensitive reagent like PTT–LA for LAC detection.
I have one more question about reporting the results of the DRVVT/Confirm and Ratio results. I was reading the ISTH 2009 and CLSI 2014 publications, and both recommend reporting out the results as normalized ratios. ISTH 2009: “Results should be expressed as ratios (normalized) of patient to NPP for all procedures. Results for Screen to Confirm Ratios should be reported as a percent correction (screen-confirm)/screen X 100.” CLSI H60: “Results should be expressed in ratios (normalized) of patient to the mean of the RI for each assay (where applicable). Clarifies that a ratio of screening and confirmatory test results for paired tests be reported either as a normalized ratio or a percent correction of normalized ratios.” Our Lab currently does not report results in this manner. To be compliant with the latest recommendations, what would you suggest that we do? Thanks.
Hi, Sheila, thanks for your question. The ISTH and CLSI recommendations are opinions from recognized experts, and do not require compliance. I’ve attached McGlasson DL, Fritsma GA. Comparison of six dilute Russell viper venom time lupus anticoagulant screen/confirm assay kits. Semin Thromb Hemost 2013;39:315–9. We computed ratios for six competing reagents normalizing on the pooled normal control plasma value, and then recomputed normalizing on the mean of the normal range. We compared both computations for all six reagents with non-normalized ratios. Out of 24 comparisons we found only one discrepant result, and in that case the normalized ratio misidentified an LA-positive sample as negative, while the “raw” ratio gave the correct interpretation.
At some recent international meetings, Dave McGlasson and I asked two laboratory directors whether their (large and prominent) labs normalizes their DRVVT results, and both said no. Based on our findings, we hold the contrary opinion that the inherent manual computation errors made while attempting to normalize results are likely to create more erroneous interpretations than normalization is likely to correct. Here is the article:
My answer is provocative and is likely to draw the attention of the authors of the ISTH and CLSI documents, so watch this space for additional comments.