A high LDH to AST ratio helps to differentiate pregnancy-associated thrombotic thrombocytopenic purpura (TTP) from HELLP syndrome

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Abstract
Objective: Differentiating between pre-eclampsia/HELLP syndrome and pregnancy-associated thrombotic thrombocytopenic purpura (TTP) is difficult but important in order to undertake timely and potentially life-saving plasma exchange (PEX) therapy for TTP recovery. We review our institutional experience with pregnancy-associated TTP and determine if the ratio of LDH to AST reliably distinguishes patients with TTP from those with HELLP syndrome. Study design: This is a retrospective case control study of all pregnant/puerperal patients with TTP from a single tertiary care center during 1986–2006. Laboratory findings in patients with TTP were compared to patients who met all criteria for class 1 or 2 HELLP syndrome within the first 24 hours of hospital admission during 2000–2007. Results: Thirteen pregnant (n = 10) or puerperal (n = 3) patients with TTP were identified; 11 cases were primary, 2 were recurrent. TTP laboratory findings included LDH to AST ratios of 77 ± 42.17; Patients with HELLP syndrome (N = 83) had significantly lower LDH to AST ratios of 20.04 ± 2.13. Based on an ROC analysis, an LDH/AST ratio ≥22.12 discriminates well between TTP and antenatal HELLP subjects (AUC = 0.99). Conclusion: A high LDH to AST ratio >22.12 suggests that TTP is a more likely diagnosis than HELLP syndrome in the third trimester pregnant patient, presenting with findings that could be compatible with either diagnosis. In these circumstances, it is advisable to obtain hematology consultation and to consider PEX implementation.

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