Abstract
A colorimetric method for the determination of free Hb in human serum is described, using 4-aminophenazone as chromogen, and commercially available hemiglobin cyanide solutions as standards. The reaction system is suitable for manual measurements as well as determinations with a centrifugal analyzer (Cobas Bio System). Accuracy, linearity and stability of the procedure is shown. A reference interval in sera of normal adults was established, with an upper limit of 5 mg/dl. The alternative use of heparin plasma instead of serum is discussed.