Despite strenuous efforts at standardization, different hCG assays
show only modest agreements with each other. Therefore, whenever serial monitoring of hCG concentrations is required, the same assay should be used for all measurements.
Transient elevations of serum hCG can occur following chemotherapy in patients with susceptible tumors, due to massive tumor cell lysis; these transient elevations should not be confused with tumor progression.
Normal serum levels of hCG do not always exclude tumor persistence since tumors may undergo transition to differentiated teratomas, which may not produce hCG.
In individuals with incomplete or complete primary hypogonadism (e.g. menopausal women, XXY males, surgically or medically castrated individuals who are receiving inadequate sex steroid replacement therapy), increased luteinizing hormone (LH)-gene transcription results in minor “leaky” transcription of hCG and hCG levels of 3-5 IU/L and, in some cases, levels as high as 25 IU/L, may be seen. In postmenopausal women, hCG levels ranging from 3.5 to 32 IU/L have been reported. In these cases, measurements of serum concentrations of sex hormones (LH and follicle-stimulating hormone) might be indicated.
End-stage renal failure is associated with up to 10-fold elevations in serum hCG levels.
Among immunometric assays, hCG assays have been found uniquely susceptible to heterophile antibody interference, resulting in occasional false positive results. Our current assay has been proven robust in this respect, but rare interferences still occur. Typically, the observed false-positive elevations are modest, ranging from just above the reference range to levels of 50-60 IU/L. If such results are seen and are discordant with the clinical picture or other biochemical or imaging tests, then the laboratory should be alerted. Rerunning the sample in question after additional blocking treatment may resolve the issue. For patients with apparent serum hCG concentrations >15-20 IU/L, hCG should also be detectable in urine, if it is truly elevated. Failure to detect urinary hCG in such patients, supports a false-positive serum hCG test.
In rare cases, interference due to extremely high titers of antibodies to analyte-specific antibodies, streptavidin or ruthenium can occur. The laboratory should be alerted if hCG values do not correlate with the clinical presentation.
In patients receiving therapy with high biotin doses (ie, >5 mg/day), no sample should be taken until at least 8 hours after the last biotin administration.