The differential diagnosis of oliguric renal failure, thrombocytopenia and thrombotic microangiopathic hemolytic anemia (MAHA) (evidenced by the red blood cell fragments, increased LDH and decreased haptoglobin) in a post partum setting includes acute fatty liver of pregnancy (AFLP), HELLP syndrome (hemolysis, elevated liver enzymes and low platelets), thrombotic thrombocytopenic purpura / hemolytic uremic syndrome (TTP/HUS), disseminated intravascular coagulation (DIC) and preeclampsia (table 1). Differentiating among these conditions is critical because they respond to different therapeutic modalities and the laboratory is often critical in making these distinctions.
|Table 1. Laboratory Differential Diagnosis
in Pregnancy Associated Thrombotic Microangiopathies*
|Abnormal PT/PTT||N||Y||N||Y||Y or N|
|Abnormal liver function tests||N||Y||Y||N||N|
|Abnormal renal function tests||Y||N||N||N||N|
|*adapted from Fricke et al|
HELLP syndrome is seen in 5% of patients with preeclamsia; 70% of cases occur antenatally and 30% occur within the first 48 hours post partum. Thrombocytopenia, microangiopathic hemolytic anemia, moderately abnormal liver function tests (LFT) and usually mildly abnormal renal function tests are characteristically present. Antepartum preeclampsia developes most commonly in nulliparous women and is characterized by proteinuria, edema and hypertension. Hemolysis is rare, and mild thrombocytopenia is present in 10-15% of cases. LFTs are minimally affected, and renal failure is rare. This patient did not have hypertension and LFTs were only transiently abnormal, making HELLP syndrome and preeclampsia less likely.
AFLP is characterized by acute hepatic failure with a significant elevation of LFTs. Renal function abnormalities tend to be mild. DIC often accompanies AFLP. This patient presented with transiently elevated LFTs with normal coagulation studies, making AFLP less likely.
DIC is a consumptive coagulopathy which may develop primarily or secondary to numerous obstetrical causes (severe preeclampsia, AFLP, retained products of conception). Patients characteristically have elevated PT, PTT, FDPs, which were lacking in this patient.
TTP/HUS is characterized by thrombosis which is localized in HUS or systemic in TTP. Coagulation studies are normal. TTP is characterized by the classic pentad of neurologic symptoms, MAHA, thrombocytopenia renal impairment and fever, but all 5 features are infrequently present. HUS presents with a triad of symptoms including severe renal impairment, variable thrombocytopenia, and thrombotic MAHA.
These conditions often will share clinical and laboratory features, and at times progress from one to another.