The Evaluation of the Partial Absorption Test for Rh Antibodies in the Prognosis of Hæmolytic Disease of the Newborn

Abstract

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.

Letter to the Editor

“…The original evaluation of the P.A. test carried out by KIRK, VOS and KELSALL [2] was based on an unselected series of 290 women in whom Rh antibodies had been detected during pregnancy. Several criteria were used for assessing the significance of the P.A.…”

Letter to the Editor

“…test carried out by Kirk, Vos and Kelsall [2] was based on an unselected series of 290 women in whom Rh antibodies had been detected during pregnancy. Several criteria were used for assessing the significance of the P.A.…”

“…titre was positively correlated with the chance of still birth, as is true also for the indirect antiglobulin titre. However, Kirk et al [2] pointed out that the P.A. titre was unreliable for detecting stillbirths unless regular titrations had been carried out from at least the 24th week of pregnancy.…”

Hæmolytic Disease of the New‐born

“…On the other hand, Kelsall and Vos (1952) claimed that they could accurately forecast the severity of the disease in the infant from the titre of the maternal antibody when this was determined hy a standardized indirect Coombs method. Kirk, Vos and Kelsall (1958) claimed that, when determined by their method, a titre at term of 1/64 or less is of no practical importance; but they give exchange transfusions to all infants when the maternal agglutinin titre is 1/128 or more. Our results and those of other workers cited above do not agree with the absolute statement of Kirk and his colleagues.…”

“…This is an interesting hypothesis, but it needs further investigation. Kirk, Vos and Kelsall (1958) claim that the " PA " titre is related to the free Rh antibody in the infant's serum, and is even more reliable as a prognostic guide than the unabsorbed titre of the maternal serum. We are unable to comment on this claim, as we have had no experience with the "P A" test.…”