Proteinuria Increases the PLASMIC and French Scores Performance to Predict Thrombotic Thrombocytopenic Purpura in Patients With Thrombotic Microangiopathy Syndrome

Introduction: PLASMIC and French scores have been developed to help clinicians in the early identification of patients with thrombotic thrombocytopenic purpura (TTP). Nevertheless, the validity of these scores in thrombotic microangiopathy (TMA) cohorts with low TTP prevalence remains uncertain. We aimed to evaluate their diagnostic value in routine clinical practice using an unselected cohort of patients with TMA. We also analyzed the value of adding proteinuria level to the scores. Methods: We retrospectively included all patients presenting with a biological TMA syndrome between January 1, 2008, and December 31, 2019, in a tertiary hospital. TMA etiology was ascertained, and scores were evaluated. Modified scores, built by adding 1 point for low proteinuria (<1.2 g/g), were compared with original scores for TTP prediction. Results: Among 273 patients presenting with a full biological TMA syndrome, 238 were classified with a TMA diagnosis. Complete scores and proteinuria level were available in 134 patients with a TTP prevalence of 7.5%. Area under the receiver operating characteristic curve (AUC) of PLASMIC and French scores for TTP diagnosis was 0.65 (0.46-0.84) and 0.72 (0.51-0.93), respectively. AUC of modified PLASMIC and French scores was 0.76 (0.59-0.92) (P = 0.003 vs. standard score) and 0.81 (0.67-0.95) (P = 0.069 vs. standard score), respectively. Specificity, positive predictive value (PPV), and positive likelihood ratio of high-risk scores were significantly improved by adding proteinuria level. Conclusion: PLASMIC and French scores have low predictive values when applied to an unselected TMA cohort. Including proteinuria level in the original scores improves their performance for TTP prediction.