[Value of the fractionation of serum immunoglobulins for the diagnosis of rubella infection in pregnant women. Critical study].

The authors present the results of fractionation by ultracentrifugation in the identification of rubella antibodies in 20 vaccinated children and 389 pregnant women suspected of having rubella. Testing for specific IgM was constantly positive when an exanthematous disease was seen in association with a significant increase an antibody level as measured by standard techniques, making questionable the reed of fractionation under such circumstances. By contrast, however, the shortest delay in collection of the first sample of serum renders fractionation essential. Alone, it made possible the diagnostic of rubella in patients in whom the first serum, although collected within 3 to 5 days after the rash, had the same antibody level as a second serum collected later. Whilst fractionisation requested for contact only without rash did not reveal specific IgM, positive results were obtained rarely in sera with a high antibody level on routine examination. The very uncertain significance of these last results, the frequency of cases of recent rubella with very modest antibody levels and the occasional finding of duodtful results, render the authors highly sceptical as to the value of fractionisation in the presence of a high serum level on routine examination in a pregnant woman.