Perils in the thrombophilia workup: Frequency and circumstances of erroneously ordered factor V activity tests for thrombophilia

Factor V Leiden (FVL) is the most common inherited thrombophilia and results from a mutation that causes resistance of coagulation factor V to inactivation by activated protein C (aPC). ¹ FVL evaluation is commonly performed in thrombophilia workups. ‘Choosing Wisely’ campaigns have suggested limiting thrombophilia evaluations to appropriate patients,^2–5 but less attention has been directed at ensuring correct tests are performed when thrombophilia evaluations are pursued. Anecdotal evidence suggests that factor V (FV) activity testing is sometimes ordered in a thrombophilia workup in lieu of FVL analysis. FV-activity provides no useful information for assessing thrombophilia.

We examined data from a large university hospital to determine the frequency and circumstances of erroneously ordered FV-activity. ⁶ Medical records were reviewed from the date of the first FV-activity result to determine the service of the ordering provider and the clinical circumstances. In patients with a documented thrombosis, we reviewed the clinical notes and laboratory data to determine if the FV-activity ordered was appropriate, erroneous (i.e. FV-activity ordered for thrombophilia workup), or uncertain. FV-activity tests were considered appropriate if ordered for the workup of an abnormal international normalized ratio (INR) or activated partial thromboplastin time (aPTT) not explained by anticoagulants, unexplained bleeding, abnormal liver function tests (LFTs) and/or liver dysfunction, or disseminated intravascular coagulopathy (DIC). At our institution, there is not a thrombophilia panel or order set and FV-activity and FVL ordering are not restricted.

Over a 6.5-month period, there were 159 FV-activity tests (122 patients), 174 FVL genetic tests (173 patients), and seven aPC resistance tests (seven patients). The majority of FV-activity orders (78%) originated from the inpatient setting. An arterial/venous thrombosis was present in 36 patients (30%) with FV-activity results. In these 36 patients, 58.3% (n=21) of FV-activity tests were ordered appropriately; 27.8% (n=10) erroneously; and 13.9% (n=5) without any apparent reason. Among the 10 patients with erroneously ordered FV-activity, half had definitive evidence that FV-activity levels were misinterpreted as a thrombophilia test. In each of these five cases, a normal or low activity level was incorrectly interpreted as a normal FVL analysis, apparent in documentation from subsequent clinical notes. Additionally, in those with erroneously ordered FV-activity, only 5/10 patients subsequently had FVL ordered or hematology evaluation. The 10 erroneous orders occurred among eight different clinical services (internal medicine, pulmonology, cardiology, neurology, family medicine, pediatric gastroenterology, vascular surgery, and burn ICU).

Although erroneous FV-activity ordering for FVL has been previously recognized anecdotally, we found no previous publications on this topic. Confusion in ordering the appropriate test for FVL is reasonably common at our institution, with FV-activity being erroneously ordered for a thrombophilia evaluation one to two times per month (or one for every 18 FVL tests ordered). Furthermore, multiple specialty services erroneously ordered FV-activity – indicating a systems-wide problem. Some FV-activity results were misinterpreted, suggesting an inherent misunderstanding of FVL testing that could have significant implications for some patients.

FVL can be assessed with a functional assay or a genetic test. Ideally, the activated protein C resistance assay (APCR), which is an aPTT-based assay that screens for FVL (in addition to other less common mutations), should be performed first. An APCR ratio < 2 indicates aPC resistance; with lower ratios suggesting a homozygous over a heterozygous mutation. Genetic testing for FVL uses PCR amplification methods to look for the presence of the R506Q mutation, the most common mutation that alters the cleavage site on activated FV. The FV-activity assay, in contrast, measures only the catalytic activity of FV.

Additional work is needed to verify the scope of erroneous FV-activity ordering and to better understand the cause of this problem. To reduce the frequency of inappropriate thrombophilia evaluations, various restrictions on ordering thrombophilia tests are enforced at some institutions (e.g. outpatients only, certain providers or services, hematology or pathology approval).^7,8 These restrictions may deter ordering by physicians less familiar with thrombophilia testing, but it is unlikely that any of these methods would be absolute in the ability to stop FV-activity from mistakenly being ordered or ultimately misinterpreted. Restricting the ordering of FV-activity to certain services could prevent erroneous ordering, but our data show that the majority of FV-activity orders were not in patients with thrombosis and restricting testing may place unnecessary burden on pathology or consult services for physicians seeking approval. A laboratory interpretation of FV-activity and/or a standard disclaimer provided with the results of FV-activity stating that the test does not evaluate FVL could be interventions that might at least prevent misinterpretation. Thrombophilia panels are available at many institutions and can help ensure the correct labs are ordered; however, panels may lead to unnecessary ordering and increased costs. ⁹ Future efforts to reduce incorrect/inappropriate thrombophilia testing should address the confusion between FV-activity and FVL in order to educate physicians and improve systems to prevent erroneous ordering.