Interference from renal dialysis patients' specimens in a direct method for serum iron.

In a direct-measuring, sample-blank procedure for serum iron we obtained spuriously high results for renal hemodialysis patients. These spurious results were found to be the result of protein precipitating out of solution owing to anticoagulation of these patients with heparin during hemodialysis. Two methods are described for circumventing this interference: adjusting the pH of the buffer and adding sodium dodecyl sulfate (lauryl sulfate). We prefer the latter procedure for reasons which are discussed, and optimized conditions are described for it. The effects on results by this latter method of bilirubin, hemolysis, and turbidity are described. The method is also evaluated for precision and accuracy, and it is recommended for routine use. A significant "protein effect" (due to viscosity) is noted, which has implications for calibration of the American Monitor KDA instrument.