Occasionally a woman will present with an elevated beta-HCG yet show no evidence of an intrauterine or ectopic pregnancy.
Differential diagnosis:
(1) false positive due to maternal antibody to animal source of immunoglobulin reagent (anti-mouse, anti-rabbit)
(2) ovarian teratoma
(3) mediastinal teratoma
(4) gestational trophoblastic disease
(5) menopause
(6) normal variation around the upper limit of normal (just above the upper limit of normal)
The presence of a positive urine test for HCG is evidence against maternal antibody since IgG should not be secreted in the urine (an exception may be in the nephrotic syndrome).
Serial dilution of the serum sample can also be helpful. A true elevation of HCG should show a proportion decrease with dilution, while antibodies causing false positives do not.
The serum AFP may be elevated in a patient with a germ cell tumor.
Close followup is important since a tumor may not become clinically evident until several months after the rise in serum HCG is detected.
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