Proportion of hemoglobin S in blood, as determined from solubility measurements.

We exploited the concentration dependence of hemoglobin S on its solubility in concentrated phosphate buffer to determine the percentage of hemoglobin S or hemoglobin A in whole blood or hemolysates. A sample is incubated for 1 h at 37 degrees C in "SickleQuik" (General Diagnostics) tubes, and the absorbance of the aqueous phase is then measured at 555 nm and 650 nm, the latter wavelength to correct for turbidity. The fractional hemoglobin S or hemoglobin A content is read from standard-curve data on mixtures of hemoglobin A and hemoglobin S. Such curves can be prepared with the use of hemoglobin A alone, because under our conditions all hemoglobin S is precipitated. The curve is reproducible for up to three weeks. Day-to-day CVs ranged from 1.8% at 10% hemoglobin S to 8.1% at 68% hemoglobin S. For similar concentration ranges, day-to-day CVs for electrophoresis, with densitometry, ranged from 4.9% to 18%. Results on 29 patients are presented. We recommend the method for rapid quantification of hemoglobin S percentage for patients with sickle cell disease in acute-care situations.