HS0048 is a group B Rh (D) negative blood sample with in-vitro antibody sensitization. Therefore, the direct antiglobulin test (DAT) of this sample should be positive and so should the weak D testing by indirect antiglobulin test (IAT). The Rh (D) status of the blood sample was therefore inconclusive in this setting and further serological test(s) was necessary to elucidate the Rh (D) status. DAT must be incorporated in parallel with the weak D testing to verify the trustworthiness of the positive result generated by the IAT.

In some red cells, Rh(D) can only be unveiled by prolonged incubation with anti-D, either directly or indirectly by means of IAT. The out-dated nomenclature, Du, was used to characterize this unique Rh(D) expression. However this obsolete termination is no longer used. Nowadays weak D is preferred and universally accepted.

Weak D testing in donors and recipients:
In blood collection centres, weak D is labelled as Rh (D) positive. Confirmatory testing of donor blood unit for weak D is not required for the hospital blood bank. Testing of recipient (patient) blood for weak D is not necessary. However, weak D detection should be included in antenatal cases to exclude candidates for Rh Immune Globulin injection.

In this exercise, it is therefore important to clarify:

1. how the sample is treated - as a recipient or as a donor;
2. yourself as a hospital blood bank or as a blood collection centre; and
3. thus the way you perform and interpret the test accordingly.

Last updated on 6 July, 2001.

Prepared by HKIMLSQAP Haematology & Serology Panel.

Copyright 2001 HKIMLSQAP. All Rights Reserved.