The direct antiglobulin (Coombs) test (DAT) may show false negative results. A negative DAT does not exclude the diagnosis of immune-mediated hemolysis.
Reasons for a false negative DAT:
(1) washing off of weakly bound globulin during the wash phase
(2) failure to use the appropriate antiglobulin to detect bound protein
(3) failure to use the appropriate temperature for temperature-dependent binding
(4) bound globulin density on the erythrocyte too low to be detected
(5) weak strength and an insensitive medium
(6) technical error
Flow cytometry and other methods may be more sensitive for identifying low density antiglobulin binding.
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