TSH, LH, FSH and hCG share a structural feature that explains cross-reactivity in some immunoassays. This shared feature is:

• A An identical beta subunit that determines receptor binding
• B A shared steroid-derived prosthetic group required for receptor activation
• C An identical 190-amino acid peptide backbone derived from the same gene
• D A common alpha subunit, while hormone specificity resides in the beta subunit ✓

Explanation

TSH, LH, FSH and hCG are glycoprotein heterodimers sharing a nearly identical alpha subunit encoded by a single gene (CGA). Each hormone's unique beta subunit confers receptor specificity and biological identity. Free beta subunits are biologically inactive until paired with alpha. Because the alpha chains are immunologically similar, assays must target the beta subunit for specificity, which is exactly why option A is wrong: identical betas would abolish hormone individuality.

Reference: Williams Textbook of Endocrinology, 14th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.