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Is DRVVT Normalization Necessary?

The clot-based dilute Russell viper venom test (DRVVT) reagent activates the coagulation mechanism’s common pathway at the factor X (10) level, relying only on factor V, prothrombin, and fibrinogen for clot formation. The DRVVT test complements the PTT-based assay for lupus anticoagulant (LAC) detection. Because LAC is phospholipid (PL)-dependent, both assays use a minimal-phospholipid (PL) “screen” and an excess-PLconfirm” reagent in sequence. A prolonged screen and shortened confirm result indicates the presence of LAC. In the DRVVT assay sequence, the result is expressed as a “screen/result ratio (SCR). Here is the formula:

DRVVT SCR = DRVVT Screen (Minimal PL) s ÷ DRVVT Confirm (Excess PL) s

The 2020 ISTH Antiphospholipid Guideline. recommends normalization of the DRVVT results using the results of pooled normal plasma (PNP) and applying the formula:

Normalized DRVVT SCR = DRVVT Screen (Minimal PL)/DRVVT PNP s ÷ DRVVT Confirm (Excess PL)/DRVVT PNP s

The textbook SCR upper limit of normal (ULN) is 1.2, confirmed by the local facility by transference. For each new PNP lot, the operator tests plasmas from at least 20 healthy subjects who represent the local population and compares results to the manufacturer’s recommended ratio—most base the ULN on the 99th percentile, or +3SD, which favors specificity over sensitivity.

Vandevelde cites the ISTH guideline in a 2022 article: Vandevelde A, Devreese KMJ. Laboratory diagnosis of antiphospholipid syndrome: insights and hindrances. J Clin Med. 2022;11:2164. doi: 10.3390/jcm11082164. PMID: 35456258; PMCID: PMC9025581.

Favaloro supports normalization in Favaloro EJ. The Russell viper venom time (RVVT) test for investigation of lupus anticoagulant (LA). Am J Hematol. 2019;94:1290–6. doi: 10.1002/ajh.25606. PMID: 31379004.

Normalization reduces lot-to-lot variation, yielding reproducible results over time. However, in his May 7 2024 Clot Club essay, Dave McGlasson cites McGlasson DL, Fritsma GA. Comparison of six dilute Russell viper venom time lupus anticoagulant screen/confirm assay kits. Semin Thromb Hemost 2013;39:315–19, stating that normalization adds no clinical differences in the interpretation of final results.

  • McGlasson’s position is supported by Zhang Y, Creer M, Oladipo OO. To normalize or not?: Dilute Russell viper venom time testing. Am J Clin Pathol. 2024  doi: 10.1093/ajcp/aqae004. PMID: 38372653.
  • Zhang’s position is questioned in a letter to the editor: Wool GD. Dilute Russell viper venom time interpretation: Influence of lot changes and normalization. Am J Clin Pathol. 2024:aqae054. doi: 10.1093/ajcp/aqae054. Epub ahead of print. PMID: 38703058.
  • Zhang challenges Wool in a follow-up letter, Zhang Y, Creer M, Oladipo OO. Reply to “Dilute Russell viper venom time interpretation: influence of lot changes and normalization”. Am J Clin Pathol. 2024:aqae051. doi: 10.1093/ajcp/aqae051. Epub ahead of print. PMID: 38703391.

(Copyright material is available from your medical library)

In our 2013 article, Dave and I contend that while normalization reduces lot-to-lot and survey CV%s, the calculated ULNs do not change clinical results and may introduce the possibility of mathematical error. We’d like to hear from our participants about their DRVVT normalization experiences. Email Geo at [email protected] or post your comment in the box below.

A comment from Bob Gosselin 5-13-24: When I did testing, we did NOT normalize.  I concur with the notion that normalizing reduces lot-to-lot variability.  I have not read Dr. Favaloro’s position, but sometimes we do stuff for those odd outliers that may be missed, but that seems like an inefficient (cost-wise) system.

Perhaps a more suitable process would be providing two PL-dependent assays (not including APTT) to rule out LA instead of a complex algorithm. Or perhaps using an LA-insensitive APTT reagent with an LA-sensitive reagent (i.e. Actin FS and Actin FSL respectively). Or perhaps, using an auto-neutralization process I described to mitigate (and why not use to confirm???) an LA: Gosselin RC. An acute need inspiration: autoneutralization of lupus anticoagulants in affected prothrombin times (PT) and activated partial thromboplastin times (APTT). Methods Mol Biol. 2023;2663:289-295. doi: 10.1007/978-1-0716-3175-1_18. PMID: 37204718. I think no process is going to be 100% diagnostic, given the heterogeneity of this antibody (what is truth?).

From Dr. Emmanuel Favaloro, 5-16-24: Hi George,
I’m offended that Bob G has not read all my papers on LA! I would agree that it is not absolutely necessary to normalize LA test results if your lab has other measures in place to control for the variability in day-to-day test measurements; LA test measurements vary according to day of testing, even without reagent lot changes. I would also make the following comments:
(a) first, I am part of a 60 lab network; although <10 of these offer LA testing, normalization permits better comparability between test results from different test sites–for example, Favaloro EJ, Mohammed S, Vong R, et al. A multi-laboratory assessment of lupus anticoagulant assays performed on the ACL TOP 50 family for harmonized testing in a large laboratory network. Int J Lab Hematol. 2022;44:654–65. doi: 10.1111/ijlh.13818. PMID: 35234361.
(b) second, although the RCPAQAP (our local external quality assessment [EQA] program) permits participants to enter non-normalised data for LA testing, we have noted that many of the errors detectable in LA testing in this EQA module arise from participants that do not normalize test data–see Favaloro EJ, Dean E, Arunachalam S. Variable performance of lupus anticoagulant testing: Tthe Australasian/Asia-Pacific experience. Semin Thromb Hemost. 2023. doi: 10.1055/s-0043-1776406. PMID: 37967835.

So, I will continue to favor normalization.


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