Origin of a false positive urine pregnancy test in a patient with membranoproliferative glomerulonephritis type I.
BACKGROUND
Discrepant qualitative urine and quantitative serum hCG results were observed in a patient with a history of membranoproliferative glomerulonephritis. Further studies were performed to investigate this discrepancy.


METHODS
Urine and serum specimens were analyzed using alternate methods and heterophilic antibody blocking and dilution studies were performed. The potentially interfering substance was identified and subsequent specimens from the patient's hospital stay were analyzed for hCG and the effect of the interferent was assessed.


RESULTS
Initially, the patient's urine specimen was positive for the presence of hCG based on the qualitative QuickVue+hCG point-of-care device. However, quantitative serum testing was negative for pregnancy on the Tosoh AIA-1800 analyzer (<2 mIU/ml). The serum specimen was also positive on the QuickVue+device, but upon incubating urine or diluted serum with heterophilic antibody binding reagent, hCG results shifted from positive to negative. Although the patient had a non-elevated human anti-mouse antibody (HAMA) level, the patient exhibited an elevated serum rheumatoid factor concentration (270 IU/ml; reference interval: ≤20 IU/ml). Application of a calibrator solution containing rheumatoid factor at levels above 175 IU/ml resulted in a positive reading on the QuickVue+point-of-care card.


CONCLUSIONS
The discrepancy between the qualitative urine and quantitative hCG results was due to an interfering substance causing a false positive on the QuickVue+urine point-of-care device. Subsequent studies identified rheumatoid factor as the potential interferent in this case.
Department of Pathology, Johns Hopkins Medical Institutions, Baltimore, MD 21287, United States.
Mark A
MA
Marzinke
Pamela
P
Jarrar
Meredith
M
Atkinson
Richard L
RL
Humphrey
Barbara
B
Detrick
Lori J
LJ
Sokoll
D006063:Chorionic Gonadotropin / Q000097:blood; D005189:False Positive Reactions; D005260:Female; D015432:Glomerulonephritis, Membranoproliferative / Q000503:physiopathology*; D006801:Humans; D011247:Pregnancy; D011258:Pregnancy Tests
D006063:Chorionic Gonadotropin