Clinical and reference lab characteristics of patients with suspected direct antiglobulin test (DAT)-negative immune hemolytic anemia.

Clinical evidence of warm autoimmune hemolytic anemia is present in 1 percent to 10 percent of patients whose direct antiglobulin test (DAT) is negative. The clinical underpinnings associated with DAT-negative immune hemolysis are poorly understood, and the current study aimed to further define the clinical characteristics associated with this form of anemia. A 19-question survey, requesting clinical information about each patient, was retrospectively mailed to all referring labs that had sent patient samples for an enhanced DAT evaluation from January 2011 through June 2013. An enhanced DAT evaluation involved a standard DAT and DATs performed using gel, polyethylene glycol, and 4°C low-ionic strength saline wash. We obtained detailed clinical information from 57 patients with an enhanced DAT investigation. Eighteen of these 57 patients (31.6%) were found to have a positive DAT, 11 (19.3%) of which were found to have a positive enhanced DAT (2 were positive by enhanced methods methods and negative by standard methods). The reported mean nadir hemoglobin for all 57 patients was 7.8% g/dL (range 3.2-12.7), and lactate dehydrogenase was 827.8 U/L (range 136-6917). Thirty-seven (18.1%) presented with a haptoglobin <10 mg/dL, and 21 (48.8%) reported spherocytes on peripheral smear. About half of the respondents reported using steroids as treatment for the anemia, and 4 of the 18 DAT-positive respondents (23.5%) changed their treatment plan because of the reference laboratory results. One patient died as a result of the reported hemolytic anemia (2.0%). We conclude that immune hemolysis detected by enhanced DAT methods is relatively common, and enhanced DAT methods are valuable tools in the diagnosis and management of patients with DAT-negative hemolytic anemia.