Case Report: Diagnosis and detection of amoxicillin-induced immune hemolytic anemia.

BACKGROUND

Drug-induced immune hemolytic anemia (DIIHA) is a rare but potentially severe adverse reaction, with antibiotics being common culprits. Amoxicillin, a widely used β-lactam antibiotic, has been infrequently reported to cause DIIHA, posing diagnostic challenges due to its nonspecific presentation.

OBJECTIVE

This study aimed to report a case of amoxicillin-induced DIIHA, detailing the diagnostic approach and laboratory methods for detecting drug-dependent antibodies.

METHODS

A 60-year-old female presented with jaundice, dark urine, and severe anemia following amoxicillin administration. Laboratory investigations included direct and indirect antiglobulin tests, antibody screening and identification, and drug-specific antibody detection using amoxicillin-sensitized red blood cells and drug-added assays. Clinical causality was assessed using the Naranjo Adverse Drug Reaction Probability Scale.

RESULTS

The patient's direct antiglobulin test was weakly positive for IgG without C3d activation. Serum showed pan-reactivity in saline, which resolved after dithiothreitol treatment, suggesting the presence of IgM cold antibodies. Serum reacted positively with amoxicillin-coated red cells in the indirect antiglobulin test but not with untreated cells, confirming the presence of amoxicillin-dependent antibodies. Hemoglobin and bilirubin levels improved after amoxicillin discontinuation. The Naranjo score was 7, indicating a "probable" association between amoxicillin and hemolysis.

CONCLUSION

Amoxicillin can induce immune hemolytic anemia through a drug-dependent antibody mechanism. A combination of detailed drug history, serological testing, and drug-specific assays is essential for accurate diagnosis. Immediate withdrawal of the implicated drug remains critical for clinical recovery.