The life-span of the red blood cell (RBC) is difficult to estimate clinically, as hemolysis may exist in the presence of normal levels of hemoglobin and bilirubin, as well as normal reticulocyte counts. Clinically useful methods for quantification of the RBC life-span include isotope methods and measurement of endogenous carbon monoxide production. Chromium 51 is the isotope most widely used but has the disadvantage of requiring blood sampling for 30 days. Measurement of endogenous carbon monoxide production has the advantage of sensitivity to low-grade hemolysis and requires only three hours of the patient's time. It is potentially useful for demonstrating changing levels of hemolysis related to drug therapy or autoimmune states.
(JAMA 230:1304-1305, 1974)