Learning from peer assessment: the role of the external quality assurance multilaboratory thrombophilia test process

Diagnostic algorithm for thrombophilia screening

Thrombophilia screening is aimed at detecting the most frequent and well-defined causes of venous thrombosis, such as activated protein C resistance/factor V Leiden mutation, prothrombin G20210A gene mutation, deficiencies of natural anticoagulants, such as antithrombin, protein C and protein S, the presence of antiphospholipid antibodies, hyperhomocysteinemia and increased factor VIII activity. At this time, thrombophilia screening is not recommended for those possible congenital or acquired risk factors, whose association with increased risk of thrombosis has not been proven sufficiently. Laboratory investigations should include a step-wise approach to the diagnosis of thrombotic disorders with respect to the assays and methods of analysis that are used. The assays recommended for the first diagnostic step of screening should establish, whether the subject has one of the common causes of thrombophilia. If one or more abnormal results are obtained, the second diagnostic step includes the assays recommended for confirmation and/or characterization of the defect. When performing the investigation of thrombophilia, it is important to consider all pre-analytical and other variables that may affect the results of thrombophilia testing, including time of testing, age, gender, liver function, hormonal status, pregnancy or the acute phase response to inflammatory diseases. This is necessary, in order to avoid, any misinterpretation of the results. This review summarizes the current knowledge concerning thrombophilia investigations, with special focus on the diagnostic algorithm regarding patient selection, the assays and methods of analysis used and all the variables that should be considered when employing tests for the diagnosis of thrombophilia.

Testing for thrombophilia: an evidence-based approach

Thrombophilia is a disorder of haemostasis in which there is a tendency for the occurrence of thrombosis. This tendency can be inherited or acquired. This review outlines common acquired and inherited thrombophilic conditions and discusses indications for testing. It is concluded that testing for acquired thrombophilic conditions should be considered in all cases of venous thrombosis, whereas testing for inherited thrombophilic conditions is unlikely to be helpful. If testing for inherited thrombophilia is to be carried out, the benefits, pitfalls and unwanted consequences of such testing should be taken into account.

Activated protein C resistance: The influence of ABO-blood group, gender and age

We have evaluated the potential influence of ABO-blood group, gender and age, on laboratory procedures used for detection of Activated Protein C Resistance (APCR), using over 300 normal donor samples and two distinct laboratory test procedures, one based on an Activated Partial Thromboplastin Time (APTT) and the other on a Russell Viper Venom Time (RVVT). We observed a statistically significant influence of ABO-blood group on APTT test times, both in the presence and absence of Activated Protein C (APC), which was no longer evident when using assay ratios. This ABO effect was not observed using the RVVT-based assay procedure. We also observed a gender effect on the APTT-based procedure, such that females (compared to males) provided shorter APTT test times (both with and without APC). This effect was still evident when using APTT assay ratios, but was again not observed using the RVVT-based procedure. We also observed an age related increase in APTT ratios. Interestingly, some previous studies have reported some specific gender and age related effects on APTT-based testing, but reports using RVVT-based testing are lacking, as are ABO related studies. Such findings should be considered as potential variables when associating specific laboratory based findings of APCR to clinical thrombophilia conditions.

Laboratory Identification of Familial Thrombophilia: Do the Pitfalls Exceed the Benefits? A Reassessment of ABO-Blood Group, Gender,Age, and other Laboratory Parameters on the Potential Influence on a Diagnosis of Protein C, Protein S, and Antithromb

Laboratory testing for familial thrombophilia defines a large proportion of the modern hemostasis laboratory workload. As part of an ongoing assessment of our activities, we have re-evaluated our laboratory procedures for antithrombin (AT), Protein C (PC), and Protein S (PS), inclusive of normal reference ranges (NRR), the potential influence of ABO-blood group, gender and age, as well as other laboratory parameters, in order to help assess the effectiveness of testing as an aid to clinical diagnosis. We did not observe a significant influence of ABO-blood group on AT, PC, or PS. However, there were gender-related effects for PS (lower in females) and AT (higher in females), but not for PC. There were also age-related effects for AT, PC, and PS. Data is compared with literature findings. We also audited the positive detection rate for PC and/or PS deficiencies. In a 6-month period of testing, we identified that 18.9% of tested samples yielded low or near-low PC and/or PS levels. However, 33.3% of such samples were potentially derived from patients on oral anticoagulant therapy (ie, potential false positives). Additional pre-analytical variables, intra-assay, inter-assay, and inter-laboratory variability also contribute to the possibility of false positive detection. Thus, whilst NRR can be developed for test parameters, the likelihood of a false-positive test result can still be shown to exceed the likelihood of a true positive result, and this casts a shadow over the clinical value of such testing in some cases. In conclusion, laboratory testing for these markers of familial thrombophilia may or may not assist in the clinical diagnosis of this condition and clinical specialists should be made aware of laboratory test limitations, and consult with laboratories prior to making a definitive diagnosis of AT, PC, or PS deficiency.