Several blood bankers have recently inquired about guidelines for Rh immune globulin (RHIG) administration following transfusion of Rh+ platelets and Plateletpheresis units to Rh- recipients. One inquiring blood banker wanted to know if there were current data quantifying the volume of red cell contamination in the typical unit of plateletpheresis.  The inquiring member was concerned that his facility was administering too much RHIG (20ug/ml red cells) based on an assumed upper limit of 5 milliliters of red cells per plateletpheresis unit. A blood bank resident (she is in an excellent training program in Northern California) stated that at her facility they occasionally run low on platelets and must give Rh positive platelets to an Rh negative male infant (less than 4 months old). She wanted to know if there was any consensus on alloimmunization of male infants to Rh incompatible products? She added that her transfusion service tells clinicians that it is unlikely that the baby will become alloimmunized, but even if that were to occur, it probably would not matter anyway, since the baby is male. However, her transfusion service does recommend administration of IV RHIG to prevent a theoretical risk of alloimmunization.

This topic was discussed with an associate as well as the Editors of the 13th and 14th (to be published) Technical Manuals. The editor of the 13th edition of the AABB Technical Manual suggested that she calculates the RHIG immunoprophylaxis dosage using 2 ml of red cells per plateletpheresis unit rather than 5 mL. According to her, we need to realize that given the current technology, most plateletpheresis units contain less than 2 mL of red cells. If a unit of plateletpheresis had 2 mL of red cells, that level of contamination would be visible. In her experience, most transfusion services would not accept visibly bloody platelet units because there are too many other units to choose from with no visible red cells. Most units with a hint of red cells are usually returned to the donor center. Also, many hospitals do not want to worry about the crossmatching of bloody-appearing products, so it is easier to return the unit than to document the visible red cells and perform a crossmatch. If you were to use such units (2 mL of red cells per plateletpheresis unit), you would give one 300 microgram vial of RHIG after every 7 Rh+ plateletpheresis units. She added that unless you were transfusing a large number of Rh+ platelets to a Rh- woman of child bearing age, she was not sure the administration of RHIG would be of benefit.

The editor of the future 14th Technical Manual commented that the 13th edition Technical Manual (page 458) states "a full dose of RhIG, which is considered immunoprophylactic for up to 15 mL of D-positive red cells, would protect against the red cells in 30 units of D-positive Platelets or 3 units of plateletpheresis. However, both the 19th and 20th editions of AABB Standards include wording to the effect that Granulocytes and plateletpheresis shall be crossmatched unless the component is prepared by a method expected to result in a component containing less than 2 mL of red cells. (Ref.: 19th ed. - I6.800, 20th ed. - 5.14.6). The 2 mL stipulation was given, as it was understood that current apheresis technology consistently produces products that contain less than 2 mls of red cells. The 14th edition of the Technical Manual will reflect this thinking and allow for a full dose of RhIg to cover 7 units of plateletpheresis. A dose smaller than a full vial of RHIG could be administered to prevent Rh sensitization; however, in practice one should probably give a full dose, as many of these patients require multiple transfusions.

And here are some comments from members of the e-Network forum:

ADDENDUM Sept. 28, 2001

1. A blood banker at a large general hospital in Northern California commented that at his facility they always recommend RHIG after administration of Rh positive platelets, regardless of the recipient's sex. They mostly issue platelet concentrates and assume a maximum content of 0.5 mL RBC/ 50 ml platelet unit. Therefore, they assume a standard dose of RhIg will cover 30 platelet concentrates, or 5 adult doses. They recommend a second dose of RHIG after 6 weeks, assuming a half-life of 3 weeks. If the platelet count is low (less than 10,000/uL), they recommend IV RHIG (WinRho) to prevent hematoma formation from an intramuscular injection.

2. A blood banker in Texas commented that at her facility Rh negative girls and Rh negative women of childbearing age receive a full 300 mcg dose of RHIG for every 30 units (or 3 pheresis) of Rh positive platelets. If a Rh- girl or woman received a single dose for Rh+ platelets or a single unit of plateletpheresis, she would still get one full dose of RHIG. The responding member's facility does not use micro amounts of RhIG. The responding blood banker added that her facility tries to avoid the problem of giving RHIG to neonates by following a policy to give only ABO/Rh type specific platelets to neonates.

3. A blood banker in Los Angeles said that someone at the ARC told her that the amount of red cells in a properly collected plateletpheresis unit was "negligible." Although what has been recommended (one 300 mcg vial of RHIG/3 units of Rh+ plateletpheresis) is OK it is quite conservative. The responding blood banker says that she has always used 1 full 300 mcg vial of RHIG to protect against 6 or 7 units of plateletpheresis that have been received within a 21-day period. She added that, "As we know, patients who chronically need platelets are less likely to make antibodies anyway. This has been shown in various studies that I am sure are well known to you."

ADDENDUM Sept. 29, 2001

4. A blood banker in Virginia commented that at his hospital, they always recommend Rh immune Globulin after transfusion of Rh-positive platelets to Rh-negative recipients. They report using an estimate of 1 mL per platelet dose (pooled or apheresis) which they think is conservative (i.e. in their experience, there is much less contamination). The responding blood banker is concerned about the comment in the introduction to this topic by one physician that the administration of RHIG may not be of benefit (even recognizing that alloimmunization is less likely in platelet recipients than healthy subjects), since it has been well demonstrated that only a few hundredths of an mL of red cells can sometimes immunize recipients. The responding blood banker says that it is his policy to individualize recommendations for repeat RHIG dosing based on the number and timing of repeated platelet transfusions. There is an approximate 21-23 day half-life for RHIG, once it has been injected, provided it is not 'consumed' by Rh+ red cells. For patients with platelet counts less than about 20,000, the responding blood banker recommends using IV RHIG, to prevent hematoma formation.

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Ira A. Shulman, MD
CBBS e-Network Forum Editor & Moderator