Rarely a blood product transfusion can result in a false-positive pregnancy test, almost always a woman..
The products usually implicated are whole blood or plasma. Packed red blood cells contain relatively little plasma but could cause a false positive under specific conditions, typically at low serum HCG concentrations.
Features:
(1) A blood product is collected from a pregnant woman. This may be before the pregnancy has been confirmed. A woman in the second or third trimester might be less likely to donate.
(2) A blood product from the collection is transfused into a patient.
(3) The patient has a pregnancy test prior to clearing the passively transfused beta-HCG.
Workup:
(1) The woman shows no evidence of pregnancy.
(2) The concentration of beta-HCG declines over the next few days.
(3) The donor segment is positive for high levels of beta-HCG.
(4) The donor has evidence of pregnancy.
(5) No other explanation for a false positive pregnancy test is identified.
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