Maureen (Mo) Tacke, St. Luke’s Health System, sent this case. A woman who had experienced one normal fetus loss at longer than 10 weeks’ gestation and one unexplained spontaneous miscarriage at shorter than 10 weeks’ gestation but no additional thrombotic episodes had the following results:
- Initial: DRVVT ratio: 1.70 (limit 1.20); silica clot time ratio 1.16 (limit <1.16); ACA, anti-beta-2-GP1, PT, PTT, and TT all normal
- 14 weeks later: DRVVT ratio: 1.39 (limit 1.20); silica clot time ratio 0.79 (limit <1.16), all other tests remain normal
George has reviewed this case with colleagues, but before posting our discussion, please comment on these questions:
- Would you consider thrombosis risk testing on a patient who has experienced two spontaneous pregnancy losses but no other thrombotic events?
- Would you consider these results conclusive for lupus anticoagulant?
- What, if any, follow-up testing would you recommend?
Please use the Comment section or respond to [email protected].
George posted this at 7:22 AM CDT, received this detailed response from Dr. Emmanual Favaloro at 11 AM CDT (3 AM, March 12, in Sydney):
Hi George,
I will not comment on the patient’s thrombosis risk, other than to say that on the face of the results, some clinicians could feasibly ‘diagnose’ an antiphospholipid syndrome (APS) based on the clinical findings and the positive LA test by DRVVT on 2 occasions. In theory, the risk of thrombosis or other clinical pathophysiology increases with multiple positivity (that is, if patients are positive for LA (+/- ACA +/- B2GPI). Also, LA seems to be the main driver, as LA positivity is more clearly linked to clinical events than either ACA or B2GPI. On the other hand, we also see positive LA in asymptomatic people, so a positive LA on its own does not diagnose APS, but given the clinical picture, it cannot be discounted.
Essentially, only one test type needs to be positive for LA to be identified–in this case dRVVT–as confirmed on another occasion as least 12 weeks apart. It also seems to be true that the dRVVT is more sensitive to LA than the APTT. However, you need to do at least 2 tests, based on different principles (eg, dRVVT + APTT), with both tests negative, before you can exclude LA.
The dRVVT appears to be positive on 2 occasions; the SCT equivocal on occasion 1 and clearly negative on occasion 2–the differences in values (rounded as 1.2 vs 0.8) is potentially concerning but I have no personal experience with this assay; all other tests negative. In general, less ‘LA’ activity seems to be present on occasion 2. I might be inclined to repeat dRVVT & SCT a third time. Is the potential reduction in LA activity on occasion 2 real, just an example of assay variation, or is it an indication that either sample 1 or 2 were ‘compromised’ (eg, by preanalytical issues).
However, before ‘diagnosing’ LA, I would like to have the following additional information: (a) what test was actually used for the dRVVT? There are some method differences. As SCT was performed, maybe this is the IL Werfen reagent? (b) were preanalytical issues excluded (eg, confirm the patient was not on any anticoagulant at the time of testing, and that the samples were appropriately collected, processed and tested – eg, double spun prior to freezing). The PT, APTT & TT were normal, so can exclude significant heparin, warfarin, dabigatran & rivaroxaban; unlikely the patient is on apixaban, but please confirm. (c) what is meant by dRVVT ratio? is this neat plasma dRVVT screen/neat plasma dRVVT confirm? Is this a normalised ratio? Were any dRVVT mixing tests performed, and if so how and with what results.
Anyone interested in reading some of my papers on this (happy to provide a copy to anyone specifically requesting by email):
- Favaloro EJ, Wong RCW. Antiphospholipid antibody testing for the antiphospholipid syndrome: a synopsis of challenges and recent guidelines. Pathology 2014;46(6):481–495.
- Favaloro EJ. The Russell Viper Venom Time (RVVT) test for investigation of lupus anticoagulant (LA). Am J Hematol. 2019 Nov;94(11):1290-1296.
- Favaloro EJ. Coagulation mixing studies: utility, algorithmic strategies and limitations for lupus anticoagulant testing or follow up of abnormal coagulation tests. Am J Hematol. 2020 Jan;95(1):117-128
Also from Bob Gosselin on March 11 at 11 PM: I confirm Dr. Favaloro’s response. Also consider a mixing study for LA testing with hex phase to confirm. Also unclear whether ACA and B2GPI were IgG and IgM only (yes, both IgG and IgM were negative, Geo). Limited data on anti-PS Abs, but with consistently pos LA, assuming at least 12 wks apart and appears to satisfy clininical and lab Sapporo criteria for LA.
Hi George,
Hi George,
My short answer to the first two questions is yes. According to the ISTH 2019 updated lupus guideline, LA testing in recurrent spontaneous early pregnancy loss is “moderately appropriate.” So, from a clinical perspective there is merit for LA testing in pregnancy complications.
A thrombotic event is not the only justification for ordering the LA testing. Although persistent (>12 weeks) positivity by a PL-dependent confirmatory coagulation assay such as dRVVT ratio will satisfy LA positivity by the lLab, the other coagulopathy factors should still be ruled out. In this case, both PT and PTT are reported normal (no PTT name is disclosed, factor and LA sensitivity is not known). So at first glance factor deficiency, specific factor inhibitors and anticoagulant therapies cannot be suspected unless there is an increased procoagulant masking effect in the sample such as elevated FVIII due to pregnancy, factor replacement therapies, etc.
A single LA positivity (i.e. the absence of anti beta-2-GP1 or ACL) does not allow a formal APS diagnosis in this case but the lab could report it LA positive subject to ruling out other interferences.
This short case summary is missing some essential information that begs clarification such as verification of clot signature in optical coagulometer (if applicable), reference interval for screen and confirm for both SCT and RVV test, patient’s screen and confirm values, was a local limit established, did LA-POS and LA-NEG controls behaved as expected. For instance, IL SCT should only be normalized according to IL’s instruction for use, did the lab follow it?
Anyway, in the absence of these details, for the next step, I will inquire about patient’s medication history, check for all preanalytical variables and repeat testing with two LA-sensitive screening assays with different mechanism (such as PTT-screen, RVV-screen) and only if at least one of them is prolonged then proceed to a mixing and confirmatory assay (in no particular order).