RESUMO
The activated protein C resistance (APCR) assay is the test of choice to screen for factor V Leiden. We evaluated the effect of lupus anticoagulant on the baseline clotting time of the second-generation APCR assay with plasma samples from 54 patients to determine whether a falsely low APCR ratio could be predicted. We also assessed whether a modification of the assay could make it more reliable in the presence of strong lupus anticoagulants. Of 54 plasma samples, 5 yielded a false-positive APCR ratio, and all 5 had a prolonged baseline clotting time. Further dilution (1:40) of the plasma samples in factor V-deficient plasma led to correction of the APCR ratio and did not affect the sensitivity of the test for factor V Leiden. Our data support that the baseline clotting time is a good predictor of a false-positive APCR test result and should be checked before calculating the ratio. The modified APCR assay reliably identified the false-positive ratios and could be used to screen for factor V Leiden in samples with strong lupus anticoagulant.
Assuntos
Resistência à Proteína C Ativada/diagnóstico , Testes de Coagulação Sanguínea/métodos , Inibidor de Coagulação do Lúpus/fisiologia , Resistência à Proteína C Ativada/sangue , Adulto , Fator V/análise , Reações Falso-Positivas , Feminino , Humanos , Inibidor de Coagulação do Lúpus/sangue , Programas de Rastreamento/métodos , Valor Preditivo dos Testes , Kit de Reagentes para Diagnóstico , Reprodutibilidade dos Testes , Sensibilidade e EspecificidadeRESUMO
A 32-year-old male presented with fever, mental status changes, renal dysfunction, cytopenias and hemolysis. His platelet count was 14,000/microL, hemoglobin 5.7 g/dL and LDH 2,636 U/L. He was diagnosed with thrombotic thrombocytopenic purpura (TTP) and also found to be HIV positive on admission. TTP was confirmed by a low von Willebrand factor-cleaving protease level, the gold standard test for TTP, which was 10-15%. No protease-specific antibody was detected. Treatment of this patient consisted of 23 plasmapheresis procedures and trials of vincristine and dextran-70. Despite therapy, the patient remained anemic and thrombocytopenic, though his mental status and renal abnormalities improved. Highly active anti-retroviral therapy (HAART) consisting of efavirenz, 3TC, and d4T was started. Only after plasma exchanges were discontinued and HAART was instituted did the cytopenias resolve. He continued to improve following discharge, and platelet count was 206,000/microL and hemoglobin, 12.5 g/dL one month after the initiation of HAART.