Practical limitations of diagnostic algorithms in heparin induced thrombocytopenia: A case report.
S. Nowak-Harnau, S. Enkel, B. Zimmermann, C. Reiss, T. Bakchoul (Tuebingen, Germany)
Platelets - Physiology and Disorders of platelet number and function
Time: 17:15 - 18:15
Objective: Heparin-induced thrombocytopenia (HIT) can be potentially associated with devastating complications such as life-threatening thrombosis making it one of the most serious adverse drug reactions. A rapid diagnostic work-up is therefore very important. However, diagnosis of HIT is challenging due to a number of practical issues and methodological limitations. We report on one case of HIT which demonstrates the limited sensitivity of a rapid assay and the 4Ts score, respectively, emphasising the need for a clear diagnostic algorithm in the clinical practice.
Methods: The pretest probability of HIT was determined using the 4Ts scoring system. A Lateral Flow Immunoassay was used as a rapid assay. Serological investigation also included an IgG-specific enzyme-linked immunosorbent assays (ELISAs) for antibodies against PF4/heparin-complexes and the Heparin induced platelet activation (HIPA) as functional assay.
Results: A 61 year old woman with a spinal cord tumour was admitted to our hospital with pain and tenderness in the right leg. Clinical examination and laboratory markers were suggestive for thrombosis. Despite treatment using low molecular weight heparin (LMWH) the patient developed a progressive thrombosis involving calf, popliteal, femoral, and vena cava. The diagnosis of HIT was suspected. First evaluation of the patient by the treating physician revealed a 4Ts score of 3. The rapid immunoassay was negative. Although these results were suggestive against HIT, we initiated further laboratory investigation and decided to switch heparin to argatroban due to the progressive thrombosis. Strong anti-PF4/heparin antibodies were detected using ELISA (OD 2.458) and HIPA (platelet activation 4/4 cells). Critical review of the medical records and direct patient,s interview revealed that the 4Ts score was miscalculated on day 7 because of (1) treatment with LMWH heparin (initially reported as s.c. insulin) before admission was not recognized and rapid-onset HIT was not considered (timing=1 point, correct 2 points), and (2) chemotherapy was considered to be a sufficient reason for thrombocytopenia (other reasons=0 points, correct 1 point). The 4Ts score was re-calculated revealing 6/8 points (high risk).
Conclusion: In clinical practice, we recommend an integrated diagnostic approach combining not only clinical assessment (the 4Ts score) but immunoassays and functional assays as well.