An e-Network member asked the forum for input on the following problem. The inquiring blood banker wanted to know the status of using serum separator tubes for blood bank testing, including their use for ABO/Rh/antibody screening and crossmatching. This question was shared with the editor of the 6th and 7th editions of AABB's "Collected Questions and Answers". The "Collected Questions and Answers" are an excellent source of practical information that can be purchased on-line through the AABB web site or by telephoning the AABB (301-215-6499).

Here is the question as it appears in the 6th edition of "Collected Questions and Answers"

"CAN SERUM SEPARATION TUBES BE USED IN THE BLOOD BANK?

QUESTION 12: Our chemistry department has started to use "tiger top" serum separation tubes and our blood transfusion specimens now arrive in these tubes. Does the silicone gel in the tubes interfere with antigen-antibody reactions or antihuman globulin serum, or is it just plain messy?

RESPONSE: "Serum separation collection tubes are not held in high regard by most immunohematologists. In addition, blood bankers do not like gel containing tubes because it is very difficult to extract red blood cells through the gel layer without the cells becoming contaminated with gel. If the gel in the red cell suspension is mistaken for agglutination in blood grouping tests there is a risk of inappropriate blood group determination. I have not heard that gel interferes with serum antibody tests. For these reasons, I recommend that you request that tubes without gel separator systems be used for blood banking purposes. Blood from gel separator tubes can be used in an emergency, but this is not recommended for routine use. Also, they're just plain messy!"

The following response was submitted:

ADDENDA Oct. 26, 2001

1. An individual with the FDA commented: "With regard to serum separator tubes, it should be noted that some package inserts specifically exclude their use, for example Immucor's Capture-R system. They reference the possibility of false-positive results. Reagent manufacturers' package inserts should always be checked for sample requirements. There is also a published article on the subject by Geisland JR, Milam, JD (Spuriously positive direct antiglobulin tests caused by use of silicone gel. Transfusion 1980:20, 6:711-713). 13% of samples gave positive results with serum separator tubes and negative results with plain glass tubes. Further testing showed that all positives were due to complement binding, as anti-IgG tests were negative and anti-C3 tests were positive. Serum separator tubes would also be contraindicated if you use an automated or semi-automated system with pipeting/dispensing equipment."

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