August 2021 – Clinical Chemistry
A 68-year-old man presented for evaluation of bilateral gynecomastia. The patient was not prescribed any medications known to cause gynecomastia, denied steroid use, and was not taking over-the-counter vitamins. Laboratory testing revealed an elevated serum concentration of β-human chorionic gonadotropin (β-hCG) (Table). The clinician contacted the laboratory to investigate whether the β-hCG test could have been affected by analytical interference. Interference studies were performed, including measuring β-hCG on an alternate platform and sample pre-treatment with a heterophile blocker (Table).
What is the most likely explanation for the elevated β-hCG result in this patient?
- Cross-reactivity of luteinizing hormone with the β-hCG assay
- Heterophile interference
- Hypogonadotropic (secondary) hypogonadism
- Hypergonadotropic (primary) hypogonadism
The correct answer is ...
The correct answer is: Hypergonadotropic (primary) hypogonadism.
Human chorionic gonadotropin (hCG) is a 36-kDa glycoprotein that is made up of two noncovalently-bound subunits (α and β). The α subunit structure found in hCG is also present in luteinizing hormone (LH), follicle-stimulating hormone (FSH), and thyroid-stimulating hormone (TSH). hCG, LH, FSH, and TSH each have a unique β subunit, however, there is a high degree of similarity between the β subunits of hCG and LH . Older generations of hCG assays were prone to cross-reactivity with LH, leading to occasional false increases in the measured concentration of hCG . To minimize any cross-reactivity with other hormones and improve the specificity of hCG measurement, current immunoassays utilize monoclonal antibodies that recognize different sites on the hCG molecule and/or different forms of hCG (i.e., “nicked” hCG, β-core fragment, free β subunit). Therefore, cross-reactivity of LH would not be responsible for the elevated hCG observed in this patient.
hCG immunoassays are susceptible to other types of interference that can result in inaccurate measurements. The presence of endogenous antibodies called heterophile antibodies is a well-known interference that typically leads to increased results with immunoassays. Heterophile antibodies can react with assay reagents, leading to signal detection in the absence of analyte. When heterophile interference is suspected, several strategies can be used to investigate, such as measuring the sample at various dilutions, using an alternate methodology or test kit (with different reagents/antibodies), or pre-treating the sample with a heterophile blocking agent. Although not performed in this investigation, HCG in urine also can be measured to help determine whether an elevated serum elevation is true. Heterophile antibodies are not found in urine, therefore a negative urine HCG with an elevated serum HCG would suggest the serum result is a false positive. In this patient’s case, the β-hCG result was unchanged after treatment with a heterophile blocker. Furthermore, assaying the sample with a different method still showed an elevated value. Therefore, the findings from the laboratory’s work-up suggested that a heterophile antibody was not present in this sample.
After ruling out potential analytical interferences, physiological causes of increased β-hCG were considered, including hypogonadism. In hypogonadotropic (secondary) hypogonadism, there is a disruption in the hypothalamic-pituitary-gonadal axis that leads to low concentrations of gonadotropins (mainly LH and FSH) and testosterone . Secondary hypogonadism is an unlikely diagnosis in this case, as the patient had high levels of LH and FSH. In hypergonadotropic (primary) hypogonadism, decreased production of testosterone results in upregulated LH and FSH secretion from the pituitary. Large increases in FSH and LH, as seen in this case, are suggestive of primary hypogonadism even with slight decreases in testosterone . In patients with primary hypogonadism, increased transcription of LH can result in “leaky” transcription of hCG from the pituitary . Pituitary secretion of hCG is often associated with concentrations in the range of 3 to 5 IU/L [6,7], and in some cases, can reach levels as high as 25-30 IU/L [8,9].
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Erica Fatica, Ph.D.
Fellow, Clinical Chemisty
Alicia Algeciras-Schimnich, Ph.D.
Consultant, Clinical Biochemistry
Professor of Laboratory Medicine and Pathology
Mayo Clinic College of Medicine and Science