CoaguChek® XS versus standard laboratory prothrombin time for anticoagulant monitoring in patients with antiphospholipid syndrome.

INTRODUCTION: The standard of care for thrombotic antiphospholipid syndrome (APS) is anticoagulation with vitamin K antagonists (VKAs). Prothrombin time, and its corresponding international normalized ratio (INR), is the laboratory test routinely performed to assess anticoagulation. Self-management of VKA therapy using point-of-care (POC) devices seems to be an attractive option. PURPOSE/OBJECTIVE: To evaluate the accuracy of a POC device (CoaguChek XS) in APS patients by comparing it with venous laboratory INR. Furthermore, we analyzed whether other clinical and laboratory features could interfere with the CoaguChek XS results. PATIENTS AND METHODS: This is a single-center cross-sectional study with 94 APS patients from a tertiary rheumatology clinic performed from August 2014 to March 2015. The comparison between CoaguChek XS and venous laboratory INR results was evaluated using the coefficient of determination (r) followed by the Bland-Altman test. A paired t-test was also applied. A difference of up to ±0.5 INR unit between the two systems was considered clinically acceptable. RESULTS: The mean CoaguChek-INR was 2.94 ± 1.41 and venous laboratory INR was 2.43±0.86, with a correlation coefficient (r) of 0.95. Categorizing INR values in ranges (INR <2, INR 2-3, INR 3-4, and INR >4), we found that the INR >4 group presented a lower correlation (r = 0.64) compared to the other ranges (p < 0.05). Although both methods were highly correlated, CoaguChek XS showed higher values than the venous laboratory INR, with an increased average of 0.42 ± 0.54. Therefore, we proposed a simple linear regression model to predict the venous laboratory INR values, using results obtained from CoaguChek XS. A difference ≤0.5 INR unit between the two systems was observed in 57.4% of patients, and the aPL profile did not influence the results. CONCLUSION: Although CoaguChek XS and venous laboratory INR demonstrated a good linear correlation in the group of INR ≤4, extra caution should be taken in APS patients, since a reasonable proportion of patients can present differences in INR results that are not acceptable. We do not recommend routine POC in APS patients.

Models for releasing the lupus anticoagulant test / Modelos de liberação do teste anticoagulante lúpico

ABSTRACT Introduction: Thrombophilia is a thrombosis susceptibility of genetic, acquired or mixed nature. Among acquired causes, the antiphospholipid syndrome (APS) stands out as an autoimmune disease characterized by antiphospholipid antibodies, thrombotic events or recurrent gestational loss. Laboratory diagnosis is based on the detection of lupus anticoagulant (LAC), anti-β2-glycoprotein 1 and anticardiolipin; however the determination of LAC still demands uniformity. The last guideline published by the Clinical and Laboratory Standards Institute (CLSI) prioritizes the screening and confirmatory steps, to the detriment of the mixing phase. Objectives: To compare the forms of releasing the LAC and to adopt an investigation protocol in agreement with the international guidelines. Methods: Thirty-six samples with prolonged results in the screening step by the dilute Russell viper venom time (dRVVT) or activated partial thromboplastin time (APTT) were subjected to the mixing steps (1:1) and to the confirmatory steps with high concentrations of phospholipids. Results: For APTT, values whose indexes of circulating anticoagulant (ICA) were greater than 15% were considered positive. For dRVVT, the ratio between screening and confirmation was also used. Of the 36 tested samples, 14 showed correction in the mixing step, but only one resulted negative. Conclusion: ICA aided in identifying the weak antibodies that were probably diluted in the mixing step. There is no gold standard test for the diagnosis of APS, and LAC detection still requires standardization of technique and interpretation.

RESUMO Introdução: Trombofilia é a suscetibilidade à trombose, de natureza genética, adquirida ou mista. Entre as causas adquiridas, destaca-se a síndrome do anticorpo antifosfolípide (SAF) - doença autoimune caracterizada por anticorpos antifosfolípides, eventos trombóticos ou perda gestacional recorrente. O diagnóstico laboratorial baseia-se na detecção do anticoagulante lúpico (ACL), do anti-β2-glicoproteína 1 e da anticardiolipina; entretanto a execução do ACL ainda demanda uniformização. A última diretriz publicada pelo Clinical and Laboratory Standards Institute (CLSI) prioriza as etapas de triagem e confirmatória, em detrimento da mistura. Objetivos: Comparar as formas de liberação do ACL e adotar um protocolo de investigação em anuência às normas internacionais. Métodos: Trinta e seis amostras com resultados prolongados na etapa de triagem pelo ensaio do tempo do veneno da víbora de Russel (dRVVT) ou tempo de tromboplastina parcial ativada (TTPA) foram submetidas às etapas de mistura (1:1) e confirmatórias com altas concentrações de fosfolipídios. Resultados: Para o TTPA, foram considerados positivos os valores cujo cálculo do índice de circulação de anticoagulante (ICA) resultasse superior a 15%. Para o dRVVT, utilizou-se também o valor da razão entre triagem e confirmatória. Das amostras testadas, 14 revelaram correção na etapa da mistura, mas somente uma resultou em pesquisa negativa. Conclusão: O cálculo do ICA auxiliou na identificação dos anticorpos fracos que possivelmente sofreram diluição na etapa da mistura. Não há um exame padrão-ouro para o diagnóstico da SAF, e a pesquisa do ACL ainda demanda uniformização da técnica e da interpretação.