e. STEP 5: Centrifuge and examine supernatant against a well-lighted white
background to detect hemolysis. Any shade of pink or red indicates hemolysis.
f. STEP 6: Record results as negative or as a quantitative estimate on
positives.
2-15. DISCREPANCIES BETWEEN CELL AND SERUM RESULTS
a. Background. When the results of cell and serum tests for ABO do not agree,
the discrepancy must be investigated. If the blood is from a donor unit, the unit must
not be released for transfusion until the discrepancy is resolved. When the blood is
from a potential recipient, it may be necessary to administer group O red cells of the
appropriate Rh type before investigations are complete. It is important to obtain enough
of the patient's blood before transfusion so that testing can be continued on a sample
free of transfused cells.
b. Sources of Discrepancies. Discrepancies in ABO testing may result from
technical errors, from intrinsic properties of the red cells, or from intrinsic properties of
the serum.
c. Technique.
(1)
Errors in technique.
(a) Dirty glassware may cause false positives.
(b)
Improper concentration of cells to serum may cause a false positive
or false negative.
(c)
Failure to identify hemolysis as a positive reaction causes a false
negative.
(d)
Over-centrifugation or under-centrifugation causes a false positive
or negative.
(e) Carelessness on reading may cause a false negative.
(f)
Warming cell-serum mixture may cause a false negative.
(g) Contamination or inactivation of reagent serums may cause a false
negative, or occasionally, false positive.
(h) Incorrect identification of specimen, materials, or incorrect
recording of results or interpretation causes false positives, false negatives, and total
disaster.
MD0845
2-19
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