[Determination of the IgE serum level: RIST or PRIST? Results of a ring test in Switzerland]

Abstract

Serum IgE concentrations, determined by two commercial kits (Phadebas RIST and PRIST) in 93 adult controls resulted in a geometrical mean value of 47 (RIST) and 35 U/ml (PRIST) respectively within a + 2 SD value of 195 and 331 U/ml respectively. The difference between the separated random samples is statistically significant (t = 3.79; p less than 1%), but the correlation is still fairly satisfactory (r = 0.79). In the lower regions the IgE values with RIST are as a rule a little higher than with the PRIST method. Surprisingly, one patient showed an extremely low IgE value (7 U/ml) with PRIST, but a considerably higher one (530 U/ml) with RIST. Such marked differences are found occasionally in the literature: heterophile antibodies against bovine gammaglobulin are regarded as responsible for the interference in the Sephadex system of RIST. As the reproducibility of the IgE determinations with the PRIST method is excellent (the correlation coefficient for two PRIST determinations was r = 0.93), and as PRIST allows much lower IgE estimates, this procedure should be given preference, particularly in pediatric patients. On the other hand, RIST must be used for the determination of extremely high values, as for instance in patients with severe atopic dermatitis or with parasitic infestations. In fact they can no longer be exactly evaluated by PRIST. Quality control of IgE serum determinations among twelve randomly chosen laboratories in Switzerland in 5 patients was satisfactory, with one exception. In the case of extremely high values, however, only a few laboratories try to determine the exact value. Indications of more than 500 U/ml were considered sufficient, with actual values amounting to 12,500 U/ml. It is also advisable to standardize the serum dilutions, the use of reference serum and the price. Finally, the indications for IgE determination are discussed. It is considered to have an important bearing on the differential diagnosis and prognosis of atopic diseases in infants and children.