A clinical audit of congenital thrombophilia investigation in tertiary practice

Thrombophilia testing in patients taking direct oral anticoagulants. Handle with care

“…This was also seen in work previously published by one of us [2], where an alarming 80% of so-called low protein C, protein S and/or antithrombin levels in diagnostic test practice derived from cases likely to be on conventional anticoagulant therapy (VKAs or heparin) at the time of testing. Thus, there is ample evidence that blood sampling for thrombophilia screening should be avoided in patients taking conventional anticoagulants such as VKAs.…”

The futility of thrombophilia testing

“…When clinicians become less selective of patients to investigate, the FVL/PGA identified becomes increasing irrelevant, with total irrelevance achieved when detection rates approach those of the normal population, since in essence this means that the normal population is being tested for these thrombophilia markers. Recent audits of clinical ordering and test practice have indeed confirmed this to be the case [9,10] (Figure 1). Moreover, the same audits have revealed that current clinical requests are simply following other natural event trends, namely births by age for women, and age-related VTE rates for males; thus, the current clinical ordering patterns simply Figure 1 Decreasing rate of FVL heterozygote detection (as a percentage of FVL tests performed) during the past 17 years at the author's institution (modified from [9,10]).…”

“…Recent audits of clinical ordering and test practice have indeed confirmed this to be the case [9,10] (Figure 1). Moreover, the same audits have revealed that current clinical requests are simply following other natural event trends, namely births by age for women, and age-related VTE rates for males; thus, the current clinical ordering patterns simply Figure 1 Decreasing rate of FVL heterozygote detection (as a percentage of FVL tests performed) during the past 17 years at the author's institution (modified from [9,10]). …”

“…Each of these anticoagulants will variably affect PC/PC/AT assays [6,7], and samples taken from patients once commenced on these drugs have a very high chance of yielding a false deficiency. We also know from audits of clinical ordering practice that between 30% and 50% of test requests for PC/PC/AT assays occur while patients are on anticoagulant therapy [8,9]. Indeed, one recent audit revealed that an alarming 80% of test cases determined to have low PC or PC or AT were likely to have derived from patients on anticoagulant therapy, and thus were potentially falsepositive events [9].…”

Protein S and protein C measurements should not be undertaken during vitamin K antagonist therapy

“…However, concentrations of PS and PC diminish during vitamin K antagonist therapy (VKA) [1,2] , and an exact diagnosis is therefore difficult to achieve during VKA therapy. Since patients with thromboembolism are likely to receive VKA therapy, it is nevertheless desirable to evaluate PS and PC during treatment, and despite general recommendations discourage investigation until VKA treatment is withdrawn [1,2] , it is unfortunately still a common procedure to draw samples during VKA therapy [3,4] . A recently published 9-month audit revealed that 144 of 194 cases (74.2 % ) with low levels of antithrombin, PS and PC appeared to be on anticoagulant therapy at the time of testing [4] .…”