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Elevated results in a vitamin B12 assay when using serum separator blood collection tubes
1Department of Clinical Biochemistry, Southern Community Laboratories Ltd, PO Box 21 049, 444 Durham Street, North Christchurch, New Zealand.
Background:
In the light of apparently spurious serum vitamin B(12) results in some patients, the effect of serum separator sample tubes on serum vitamin B(12) values, assayed by the Bayer Centaur analyser, was examined.
Method:
Results of parallel assays of serum vitamin B(12) in plain (non-gel) serum tubes and serum separator gel tubes were compared. Serum in previously centrifuged gel tubes was mixed in the tube and the effect of that mixing on assay results quantitated. A limited investigation of the effect of tube cap type was also carried out.
Results:
Serum vitamin B(12) concentration was 54% higher in samples taken into serum separator tubes after re-mixing the serum in the original tube. This effect could be abolished by re-centrifugation.
Conclusions:
Use of serum separator tubes may be associated with spuriously elevated serum vitamin B(12) concentrations in the Bayer Centaur assay. Laboratories receiving samples for vitamin B(12) assay in serum separator tubes that have already been centrifuged should either re-centrifuge the tubes, or aliquot and re-centrifuge serum from the tubes prior to vitamin B(12) assay.
