Easy fix for clinical laboratories for the false-positive defect with the Abbott AxSym total beta-hCG test.
BACKGROUND
False-positive hCG results can lead to erroneous diagnoses and needless chemotherapy and surgery. In the last 2 years, eight publications described cases involving false-positive hCG tests; all eight involved the AxSym test. We investigated the source of this abundance of cases and a simple fix that may be used by clinical laboratories.


METHODS
False-positive hCG was primarily identified by absence of hCG in urine and varying or negative hCG results in alternative tests. Seventeen false-positive serum samples in the AxSym test were evaluated undiluted and at twofold dilution with diluent containing excess goat serum or immunoglobulin.


RESULTS
We identified 58 patients with false-positive hCG, 47 of 58 due to the Abbott AxSym total hCGbeta test (81%). Sixteen of 17 of these "false-positive" results (mean 100 mIU/ml) became undetectable when tested again after twofold dilution.


CONCLUSIONS
A simple twofold dilution with this diluent containing excess goat serum or immunoglobulin completely protected 16 of 17 samples from patients having false-positive results. It is recommended that laboratories using this test use twofold dilution as a minimum to prevent false-positive results.
Cole
Laurence A
LA
Department of Obstetrics and Gynecology, USA hCG Reference Service, University of New Mexico, Albuquerque, NM 87131, USA. larry@hcglab.com
Khanlian
Sarah A
SA
D000818:Animals; D000910:Antibodies, Heterophile; D016477:Artifacts; D018997:Chorionic Gonadotropin, beta Subunit, Human / Q000097:blood*; D019963:Clinical Chemistry Tests / Q000379:methods* / Q000592:standards / Q000706:statistics & numerical data; D003951:Diagnostic Errors / Q000517:prevention & control* / Q000706:statistics & numerical data; D005189:False Positive Reactions; D005260:Female; D031901:Gestational Trophoblastic Disease / Q000175:diagnosis; D006041:Goats; D006801:Humans; D007118:Immunoassay / Q000379:methods* / Q000592:standards; D007136:Immunoglobulins; D007753:Laboratories; D011247:Pregnancy; D011259:Pregnancy Tests, Immunologic / Q000706:statistics & numerical data; D044967:Serum
D000910:Antibodies, Heterophile; D018997:Chorionic Gonadotropin, beta Subunit, Human; D007136:Immunoglobulins