Graded hemagglutination inhibition for quantification of human fetal hemoglobin.

We describe a hemagglutination system for quantification of fetal hemoglobin (HbF), especially at low concentrations. This system consists of three components: (a) sheep erythrocytes coated with purified HbF, (b) sheep antiserum of human HbF made specific for the gamma-chain, and (c) human blood lysate with a known concentration of HbF as the standard. We can measure the whole range of HbF proportions in human blood, from 100% down to 0.01%. Statistical analysis showed that our measurements agreed with those made by the methods of alkali denaturation and radial immunodiffusion. Reproducibility of the method is shown by the low CVs for six repeated measurements. Low concentrations of HbF not measurable by other methods are easily assayed. We offer examples of the clinical utility of data on low concentrations of HbF.