hCG Does Not Increase FSH or LH—Rather, the Reverse Occurs: LH Cross-Reacts with hCG Assays
The question is backwards: hCG does not raise FSH and LH levels. Instead, elevated LH (particularly in hypogonadal states) can cross-react with hCG immunoassays and produce falsely elevated hCG readings. 1
The Actual Mechanism of False-Positive Results
LH Cross-Reactivity with hCG Assays
LH can cross-react with some hCG immunoassays because hCG and LH share an identical alpha subunit and have structural similarities. 1, 2
This cross-reactivity is particularly problematic in hypogonadal patients (such as those post-orchiectomy or post-chemotherapy) who develop compensatory elevations in pituitary LH and FSH secretion. 1
The American Society of Clinical Oncology guidelines specifically warn that "unilateral orchiectomy and chemotherapy can cause low testosterone levels, which in turn can lead to increased production of LH and hCG by the pituitary gland. LH can cross-react with some assays for hCG." 1
Clinical Evidence of the Problem
In men with solitary or absent testes, 41% had falsely positive commercial hCG determinations due to elevated LH levels and cross-reactivity. 3
There was a striking correlation between elevated serum LH levels and falsely elevated commercial hCG levels in men with gonadal dysfunction. 3
Falsely elevated hCG values (1.7-7.8 mIU/ml) occurred in patients with complete tumor response who had simultaneously elevated LH (18-79.9 mIU/ml) and FSH (5-80 mIU/ml) due to iatrogenic hypogonadism. 4
What Actually Happens When hCG is Administered
hCG Suppresses FSH, Not the Reverse
When hCG levels exceed 100 U/L, subtotal inhibition of FSH secretion occurs. 5
In patients treated with GnRH agonists plus hMG, exogenous hCG administration led to a significant fall in LH levels, not a rise. 6
hCG acts like LH to stimulate testosterone production, which through negative feedback suppresses pituitary gonadotropin release. 1
Clinical Management of This Assay Interference
How to Identify False-Positive hCG
Check FSH levels from the same serum sample. If beta-hCG is elevated but FSH is also excessively elevated (>50 U/L), the hCG elevation may be due to LH cross-reactivity rather than tumor. 5
Administer supplemental testosterone to hypogonadal patients, which reduces gonadotropin-releasing hormone and consequently suppresses pituitary production of LH and hCG, normalizing the falsely elevated hCG reading. 1, 4
Each laboratory should establish the degree of cross-reactivity with their specific gonadotropin assay, and physicians should inform the laboratory when patients are on hCG therapy if gonadotropin levels are requested. 2