Anti-D antibodies : In vitro tests to predict the severity of hemolytic disease of the newborn

Sammanfattning: The ability of different in vitro tests to predict the severity of hemolytic disease of the newborn (HDN) has been studied. When properly performed the traditional indirect antiglobulin titers (IAT) on maternal serum can be used to identify a low !iter group ~32 in which the fetus will not suffer from severe hemolytic disease and a high titer group ~1000 where all newboms will be affected. However, in the titer interval64-512, the prediction by IAT titers is poor and additional tests are needed. Widely used are determination of the anti-D concentration in maternal serum and measurement of the bilirubin concentration inamniotic fluid, the latter requiring amniocentesis (AMC). The negative predictive value using bilirubin measurements was 0.53 and using anti-D concentration determination 0.73. This shows that no further information is gained by adding amnion fluid examination if anti-D concentration determination is carried out. Moreover, as invasive procedures such as AMC may be dangerous to the fetus, it is preferable to use measurements of anti-D concentration, requiring only a venous blood sample from the mother. AutoAnalyzers have been used for 25 years and are still the main instrument for determining anti-D concentration. As this test is important in the prediction of HDN, there is an obvious need for a modern and reliable method of anti-D quantitation. A new method using flow cytometry was developed and found to give exactly the same classification as the AutoAnalyzer in 89% of cases. In the !I% that differed, the flow cytometer found more relevant cases than the AutoAnalyzer. The IgG subclass of the maternal anti-D can be of importance for the outcome in the newborn. To perform IgG subclassing of anti-D, a method using the gel technique was elaborated. Among severely affected cases, two or more subclasses were detected in 77%, compared to 20% in moderately or unaffected cases. When used as a complementary test in borderline cases having anti-D concentrations 0.6-1.4 jlg/mL_, no cases at risk of HDN would be missed and cases where additional invasive procedures must be performed would bereduced by about 60% (in the present series from 22to 9). HLA typing revealed the HLA DQB 1 a!lel '020 I to be four times more common in women with severe immunizations than in those with low levels of anti-D. Typing for this allel may be a means of identifying women with a high risk of developing severe immunizations.

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