Background: The glycoproteic hormones, LH and FSH, circulate under heterogenous molecular forms, the isoforms. The more acidic isoforms of FSH are found in hypogonadic patients and a displacement towards the basic forms is observed during substitutive treatment.
Case report: A 13 year-old girl with Turner syndrome was examined for pubertal delay. Ultrasonography failed to see both ovaries and endocrine investigations showed a type P1 response (LH-RH test using immunological method). Control of hormonal levels by a polyclonal immunoenzymatic method confirmed primary hypogonadism.
Conclusions: Radioimmunological methods using monoclonal antibodies can underevaluate FSH and LH levels under circumstances in which the distribution of isoforms may vary. Discrepancy must lead to the measure of gonadotrophins using polyclonal immunoenzymatic methods.