Screening for primary immunodeficiencies associated with purine nucleoside phosphorylase deficiency or adenosine deaminase deficiency.

A screening method has been established for PNP deficiency. This enzyme activity in dried blood absorbed on filter paper can be detected by the formation of a blue insoluble formazan with a gel containing inosine, xanthine oxidase, MTT-tetrazolium, and phenazine methosulfate. The color change is very clear and definite and no false results have been obtained in the testing of 256 enzyme-positive and 107 enzyme-negative samples. The enzyme activity in dried blood on filter paper is so stable at room temperature that samples can be mailed. A screening method for ADA deficiency was developed, also depending on the color change of MTT-tetrazolium. Although the test is slightly more expensive than that developed by Moore and Meuwissen, its accuracy is greater. A common screening method for detecting deficiencies of either PNP or ADA is described.