D and Weak-D Testing

[JClausen]

We are planning to drop weak-D testing on all patients except for cord-bloods of Rh neg moms and autologous donor/patient testing discrepancies. I would like to know what other facilities are doing for the following pre-transfusion testing situations. :

In one of the weak-D threads, a forum member mentioned that if the results of the immediate spin D typing is neg to 1+ they consider the patient Rh negative. I am interested to know if there are any other facilities that have this policy, or is the usual interpretation RH pos for any strength of reactivity on the immediate spin testing.

Also, if when doing weak-D testing on a cord blood to determine if the mom needs RHIG, the result is weak-D positive, is this infant considered Rh positive for transfusion purposes or Rh negative? Does anyone use a strength of reactivity to make this decision?

[lef5501]

Most of our tests are done in gel and if the Rh comes up pos in gel, then we consider the sample pos., no matter what strength it appears. This is due to the fact that the gel is so sensitive. We researched this at some other facilities and most of the larger facilities we talked, don't even do weak D testing if it comes up neg with gel.

Our policy is slightly differerent for tubes. In tubes, if the weak D comes up < 2+, we call it neg and if it is greater than 2+ than we call it pos.

[johna]

Our reference laboratory seriously considered dropping the weak D test until we ran into a couple of roadblocks. The first was the cord blood issue. We eventually decided that we should be able to identify cord bloods so that a weak D test could be performed. The second obstacle was not so easy. How about situations in which a specimen is submitted for Rh typing on the husband of an Rh-negative prenatal patient. We have encountered a very small number of OB physicians who base Rh immune globulin candidacy on the Rh type of the husband. If we fail to recognize that this is a paternal specimen and that the husband is a weak D, the prenatal patient will not receive RhIg. I would think there would be some liability on our part if this was the case. Any thoughts?

[adiescast]

We do weak D testing only on the following:

1. Cord bloods of babies with Rh negative mothers

2. Patient test Rh negative, but autologous blood is labeled Rh positive.

3. Patient with anti-D, for antigen typing on initial identification

4. Partners (putative fathers) of Rh neg­ative women with obstetric diagnoses.

We do not include the weak D result when determining the patient's overall Rh type. A weak D positive person is reported as Rh negative, weak D positive. For transfusion purposes, the person would be given Rh negative blood. We do not use reaction strength as a guideline. Any positivity in the D or weak D test is a positive result on the test.

For determining maternal RhIg, the mother would get RhIg regardless of her weak D status. We recommend RhIg for mothers of weak D positive infants or with weak D positive partners. We do place the burden of identifying the putative father on the obstetrician. If they don't identify the sample, there is no way for you to know what it is (although getting a male sample from an OB clinic is a pretty good hint!).

I hope that helps!

[Cathy]

Hi, We are in the process of dropping weak D testing. I have another question related to this subject. Would you change the historical type of a patient who previously typed weak D positive to Rh negative now? Or would you continue testing the weak D on this patient to keep the type the same? We will also continue to test babies and autologous donors for weak D. We have not yet considered the scenario of the alleged father and possibility of liability, thanks for bringing that up!

[donellda]

We no longer do weak D testing except for the situation of an Rh D negative mother with a baby whose cord blood tests as Rh D negative also. We do the weak D in case the baby is weak D positive so that we can give the mother Rhogam.

When we do a weak D on a patient, their is a comment put in the patient's permanent blood bank record so that the weak D test does not have to be repeated, although we no longer do the test:). We have changed patients Rh D type when we have found them to be, in fact Rh D positive, from previously testing as negative due to newer antisera that can pick up weaker D reactions now.

[Dar]

I have 2 questions for those of you who have dropped the "weak D" test.

1. Do you require your techs to perform "weak D" as antigen typing if an anti-D is identified?

2. If you have a "weak D+" newborn, how is it reported? Do you report it as Rh negative to eliminate the confusion when it returns in later years?

Thanks!

Dar