Association between NT-proBNP and false-positive Coombs test in patients with heart failure and elevated NT-proBNP

The human antiglobulin test or Coombs' test is a key tool in the diagnosis and classification of haemolytic anaemia and could present as falsely positive. A retrospective study has described that B-type natriuretic peptide (NT-proBNP), a biomarker used for heart failure (HF), could be an additional cause of false positives in the Coombs test.

A prospective, observational, single-centre study was conducted in adult patients diagnosed with HF between October 2024 and March 2025 at a tertiary hospital. The Coombs' test was considered as false positive in cases in which the specificity of the test included immunoglobulin G (IgG), the subsequent elution yielded a negative result, and blood haemolysis parameters were within normal ranges.

Thirty-six patients were included, of whom nine (25%) had a false-positive Coombs test. These patients had significantly higher levels of NT-proBNP (10,825 pg/mL [2587-35,000] vs. 3314 pg/mL [278-11,856], p = 0.0076) and lower glomerular filtration rate (35.3 mL/min/1.73 m² [23.6-46.3] vs. 63.3 mL/min/1.73 m² [21.9-90.0], p = 0.0055) compared to patients with a negative Coombs test. No statistically significant associations were found with drugs used concomitantly for HF.

The results suggest that elevated NT-proBNP could also be a cause of false positives in the Coombs test.