Spurious undetectable albumin due to hemodialysis catheter lock contamination.

BACKGROUND: Contamination of blood drawn through a hemodialysis catheter with heparin lock solution can interfere with albumin measurement by the bromocresol green (BCG) method, which shows dose-dependent negative interference with heparin. Catheter lock solutions (1000-5000 U/mL) are far more concentrated than the heparin used in standard collection tubes and pose a correspondingly greater risk of interference. CASE: In a 46-year-old man on maintenance hemodialysis, a routine sample drawn from a tunneled permanent catheter without discard of the lock solution yielded an albumin below the analytical measuring range (<2 g/L) in a clinically stable patient with no signs of severe hypoalbuminemia. Analytical error was excluded by an unchanged repeat measurement and acceptable internal quality control performance. A repeat sample, drawn after an appropriate discard volume, gave an albumin of 42 g/L, confirming heparin contamination as the cause. CONCLUSION: Catheter lock solution heparin can produce an analytically uninterpretable albumin result by the BCG method. Adherence to evidence-based discard volume protocols is essential in dialysis units.