Distinguishing thrombotic thrombocytopenic purpura from primary immune thrombocytopenia accompanied by anemia using the carbon monoxide breath test.

OBJECTIVES: Thrombotic thrombocytopenic purpura (TTP) is a rare but life-threatening hematological disorder. Early differentiation between TTP and primary immune thrombocytopenia (ITP) accompanied by anemia is crucial to initiate an appropriate therapeutic strategy. The objective of this study was to evaluate the predictive value of red blood cell lifespan (RBCLS), determined using the carbon monoxide breath test, in the differential diagnosis of these two diseases.

METHODS: We conducted a retrospective analysis of 23 patients with TTP and 32 patients with ITP accompanied by anemia. RBCLS measurements were compared and evaluated between these two patient groups.

RESULTS: TTP patients had a significantly shorter mean RBCLS (20 ± 8 days) than patients with ITP accompanied by anemia (77 ± 22 days, P  < 0.001) and healthy controls (114 ± 25 days, P  < 0.001). In TTP patients, RBCLS showed a significant negative correlation with reticulocyte percentage and lactic dehydrogenase levels ( P  < 0.001). When using a standard baseline of 75 days, RBCLS demonstrated a sensitivity of 100% and specificity of 53.1% in identifying TTP. The diagnostic accuracy could reach 93% by excluding the impact of gastrointestinal bleeding. By employing the Receiver Operator Characteristics (ROC) curve, the area under the curve for RBCLS was 0.985 (95% CI: 0-1, P  < 0.01) in predicting TTP, with an optimal cut-off value of 32 days, and sensitivity and specificity of 95.7% and 96.9%, respectively.

CONCLUSIONS: Our study proposes a simple and accessible method for evaluating RBCLS to differentiate between TTP and ITP accompanied by anemia.