SummaryThe partial absorption test for titrating Rh antibodies in the maternal serum has been evaluated as a prognostic tool in a series of 290 cases of infants born to Rh‐immunized women. The P.A. test enables a more accurate prognosis to be made of the outcome for the infant than if the indirect antiglobulin titre of the maternal serum is used alone.The statistical coefficient of correlation between the P.A. titre of the maternal serum at the time of birth and cord blood haemoglobin for liveborn Rh‐positive infants is ‐0.72.The P.A. titre is unreliable in predicting stillbirths unless regular titrations have been carried out at least from the twentyfourth week of pregnancy. The unreliability is due to the rapid fall in P.A. titre in many cases after the foetus has died in utero. However, if the P.A. titre at the end of the second trimester is 1 : 64 or higher, the outcome is almost invariably fatal.The use of the P.A. test in conjunction with the ordinary indirect antiglobulin titrations of the maternal serum enables a more accurate discrimination to be made between mild and severe cases of hæmolytic disease of the newborn. It also makes possible the more reliable diagnosis of an Rh‐negative infant in cases in which the father is known to be heterozygous D/d, and is a valuable guide for giving advice to parents of Rh‐affected infants on when to start another pregnancy.It is recommended that exchange‐transfusion should be carried out in all cases in which the maternal indirect antiglobulin titre at the time of birth is 1 : 256 or higher. Exchange‐transfusion is not warranted if the maternal indirect antiglobulin titre is less than 1 : 128 at the time of birth. Where the maternal indirect antiglobulin titre is 1 : 128, exchange‐transfusion is not necessary if the P.A. titre is zero.

SummaryA new test is described which enables the quantity of Rh antibody free in the fœtal serum to be estimated by titrations carried out on the maternal serum. Equal volumes of a hæmolysed 25% suspension of Rh‐positive red cells and a 1 : 4 dilution of the maternal anti‐Rh sera are incubated at room temperature for 15 minutes. The Rh antibody remaining free at the end of this time is titrated by the indirect antiglobulin method. The titre value obtained is referred to as the partial absorption (P.A.) titre.The P.A. titre is closely related to the titre of free Rh antibody in the cord serum of the infant at birth. The P.A. titre also is highly correlated with the blocking titre, but shows no relationship with the conglutination or albumin titres. The P.A. test, however, is more sensitive than the blocking test in detecting Rh antibodies of pathological significance, and is likely to be therefore of greater prognostic value.

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