August 2021 – Clinical Chemistry

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 [1]. Older generations of hCG assays were prone to cross-reactivity with LH, leading to occasional false increases in the measured concentration of hCG [2]. 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 [3]. 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 [4]. In patients with primary hypogonadism, increased transcription of LH can result in “leaky” transcription of hCG from the pituitary [5]. 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].

References

1. Tietz Fundamentals of Clinical Chemistry and Molecular Diagnostics, 8th edition. Chapter 44: Pregnancy and Prenatal Testing. 2020
2. Braunstein GD. False-positive serum human chorionic gonadotropin results: Causes, characteristics, and recognition. AJOG Reviews. 2002;187(1):217-224.
3. Belchetz PE, Barth JH, Kaufman JM. Biochemical endocrinology of the hypogonadal male. Ann Clin Biochem 2010;47:503–15.
4. Contemporary Practice in Clinical Chemistry, 4th Edition. Chapter 38: Laboratory Testing in Pregnancy and Reproductive Disorders. 2020
5. Santen R, Hasan F, Thoren K, Farooki A. Pituitary as a Source of HCG: Residual Levels After Bilateral Testicular Tumor Removal. J Investig Med High Impact Case Rep. 2019;7:2324709619841414. doi:10.1177/2324709619841414
6. Yoshimura K, Nakashima Y, Sugiyama K, Kohei N, Takizawa A. Supposed pituitary-production of human chorionic Gonadotropin induced by androgen deprivation therapy. Int Braz J Urol. 2019 Jan-Feb;45(1):38-44. 
7. Snyder JA, Haymond S, Parvin CA, Gronowski AM, Grenache DG. Diagnostic considerations in the measurement of human chorionic gonadotropin in aging women. Clin Chem. 2005 Oct;51(10):1830-5.
8. Cole LA, Khanlian SA, Muller CY. Detection of perimenopause or postmenopause human chorionic gonadotropin: an unnecessary source of alarm. Am J Obstet Gynecol. 2008 Mar;198(3):275.e1-7.
9. Cole LA, Sasaki Y, Muller CY. Normal production of human chorionic gonadotropin in menopause. N Engl J Med 2007;356:1184-1186.