Special Blood Bank Tests

A. Platelet antibody testing.

Platelet antibody testing cannot be performed at night or on the weekend. Have the daytime resident follow-up on these requests if necessary. Make sure the clinicians don't want a heparin-associated antibody test, which is handled through Hematology. Platelet antibody testing will require a fresh specimen of blood drawn the morning it is to be shipped to the reference lab, therefore samples should not be sent down at night or on the weekend.

B. HLA testing.

PMH does not perform HLA testing. Dr. Peter Stastny's lab at UT Southwestern does some transplant HLA testing. HLA testing for platelet donors must be arranged during regular working hours through BloodCare. See HLA-matched platelets.

C. Anti-A or anti-B titers.

These titers are sometimes called isohemagglutination titers. We get requests to perform titers for the following circumstances:

ABO-incompatible liver transplant recipients. Titers are necessary daily to determine the risk of humoral rejection and are used to decide whether plasmapheresis will be performed that day. Because they are used to order plasmapheresis, they need to be performed early in the day and on weekends as well as weekdays. Generally, a titer of 8 or greater will necessitate plasmapheresis.
Suspected parasitic disease. Most commonly, titers are requested in children suspected of having visceral larva migrans (Toxocara infection). Parasites such as Toxocara, Ascaris, Schistosomiasis, and malaria express A and B-like substances on their surfaces, eliciting increases in anti-A or anti-B titers in patients who already have those antibodies. The problem with performing anti-A or anti-B titers in this situation is that individual variation in titers makes a single one-time measurement unhelpful for the diagnosis of visceral larva migrans. For example, if the patient's anti-A titer is 256, what does that mean? If you had a baseline measurement of 32, then you would know it was elevated. But we never have a baseline measurement for comparison, thus a titer of 256 may well be normal. (Mollison's text says that 95% of people with anti-A have titers between 32 and 2048, with 256 being the most common, while anti-B titers range between 8 and 512, with 64 being the most common. Pre-adolescent children have the highest titers.) Comparing an acute serum sample with a convalescent serum sample is probably the best that you can do (did the titer go up during that time significantly?)
Occasionally someone asks for isohemagglutinin titers to assess a child's immunoglobin status (part of a work-up for immunodeficiency). There are probably better tests that can be performed in Immunology.

Your job is to decide if the titers should be performed, and if so, can they wait until regular working hours when more staff are present. For liver transplants, they will need to be done on the weekend. For parasite diagnosis they can usually wait until the next working day, or better yet, you can convince them that the titer will not be especially helpful.

D. Fetomaternal hemorrhage (FMH) testing.

The purpose of FMH testing in the blood bank is to determine which Rh negative mothers delivering babies are at risk for D antigen sensitization from having a larger-than-expected FMH. Those having a larger than normal bleed may need to receive additional vials of RhIG. PMH blood bank performs the rosette test within 24 hours following delivery on all unimmunized Rh negative women. This test is a qualitative test that looks for D-antigen-positive RBCs in the maternal blood specimen. Rosette tests are performed at least twice daily. A positive rosette test is followed immediately by a Kleihauer-Betke acid elution stain, performed in the Hematology lab. These must be done even on weekends so that postpartum women can get additional vials of RhIG if needed and be discharged in a timely manner. The Kleihauer-Betke stain looks for cells containing fetal hemoglobin rather than RBCs displaying D antigen. The ratio of fetal to maternal cells tells you how large an FMH occurred. A formula in the blood bank procedure manual (taken from the AABB Technical Manual) tells how many additional vials of RhIG are then necessary for that size of bleed. We must round "up" numbers if the ratio falls between two cut-offs for additional vials so that enough RhIG will definitely be given. See appendix 8 in paper supplement.

You may be called in the case of a positive rosette test, or perhaps for the case of a Kleihauer-Betke stain indicating the need for additional RhIG. However, blood bank staff will generally take care of calling the floor to notify them of the extra-large bleed. The daytime blood bank resident then writes a formal consultation for the chart.

E. RBC eluate using penicillin-treated reagent cells.

You may get a request to approve an eluate which will be tested against a panel of penicillin-treated RBCs. This request should only be considered in the clinical setting of a patient with hemolysis thought due to anti-penicillin antibodies. The patient should have a history of receiving large doses of penicillin intravenously in the recent past. The DAT should be positive for IgG in such patients, but a routine eluate is negative. You may approve this test if it sounds indicated, but generally there is no need to perform it on a STAT basis (e.g. after hours or on the weekend). If this diagnosis is strongly suspected, the patient will have had their penicillin infusion terminated, necessitating no need for additional treatment.

F. Blood typing.

PMH Transfusion Services does not provide blood typing to whole blood directed donors prior to their donation. We do not have the resources to offer this service. BloodCare can perform these tests for a certain fee, paid up front. Call BloodCare Special Donations for more information.

Phone requests for blood types. If anyone calls the laboratory asking to be told a blood typing result, that information will not be released over the phone. If a doctor calls from a remote OB clinic and needs to know Mrs. X's blood type so he knows whether to give her RhIG or not and he doesn't have access to a computer terminal, we can fax him the result. However, we won't give it verbally because too many errors have occurred from the caller mistranscribing the blood type on the patient records.

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