Haptoglobin typing, is it clinically necessary for a reliable determination of haptoglobin with the single radial immunodiffusion technique?

Over a period of three years we determined haptoglobin levels by single radial immunodiffusion (RID) and the haptoglobin phenotype in over 1700 samples of patients suspected of a haemolytic disease. As haptoglobin phenotyping is rather laborious and therefore an expensive method, we re-evaluated the diagnostic need for phenotyping. From our reference values for the respective phenotypes of haptoglobin it may be theoretically argued that phenotyping is still desirable when the RID value is in the range 400-1170 mg/l. Limiting ourselves to suspected haemolytic diseases, one can abolish phenotyping beyond this narrow range without withdrawing important clinical information. From the total group it appeared that 480 samples lay in this range. In 72 samples (15% of 480) the evaluation of the RID values was essentially altered by phenotyping. Careful examination of the medical records indicated that in a number of cases laborious phenotyping had indeed contributed to the diagnosis.