Inhibin B plus baseline LH levels aids hypogonadotropic hypogonadism diagnosis in boys

By Lucy Piper, Senior medwireNews Reporter

Researchers recommend measuring inhibin B concentration in combination with basal luteinising hormone (LH) as a first-line test to discover the underlying cause of delayed puberty in boys.

They found that inhibin B concentration, at a cutoff level of below 111 pg/mL, distinguished isolated hypogonadotropic hypogonadism (IHH) from constitutional delay of growth and puberty (CDGP) in 61 boys with 100% sensitivity.

This level of sensitivity was comparable to that for an LH response of below 5.3 IU/L 4 hours after receiving a gonadotropic-releasing hormone agonist (GnRHa), although testing inhibin B concentration alone was less specific, at 92.3% versus 100%.

However, combining inhibin B concentration with a basal LH measurement of below 0.3 IU/L increased specificity to 98.1%. And the diagnostic accuracy of the combined basal test did not differ significantly from that achieved with the GnRHa test, at 98.4% and 100%, respectively.

The team, led by Gerhard Binder (University Children’s Hospital, Tuebingen, Germany), notes that the findings suggest that a combined basal test of inhibin B plus LH “is a very attractive alternative to the GnRHa test”.

They expand: “The basal test is less invasive, less time-consuming and less expensive.” The team therefore recommends that “[t]he GnRHa test may be reserved for cases with equivocal basal test results.”

Discussing the findings with medwireNews, Leo Dunkel, Professor of Paediatric Endocrinology and Metabolism at Barts & The London School of Medicine and Dentistry in the UK, agrees that inhibin B is useful in such diagnostics, but inconsistencies in published findings to date mean that it is “not fully adopted by all colleagues”.

The study, published in Clinical Endocrinology, involved boys aged 13.7 to 17.5 years with a maximum testicular volume of 4 mL. At 12–18 months of follow-up, 52 boys were diagnosed with CDGP, based on having a testicular volume of at least 8 mL, while IHH was diagnosed in nine boys whose testicular volume was no more than 5 mL after 24 months of follow-up.

The researchers also identified some physical differences between the two diagnostic groups that they believe could help guide diagnosis when hormone test results are borderline.

These included milder growth retardation with concomitant milder bone age retardation in boys with IHH than in those with CDGP and a body mass index below the reference mean in boys with CDGP but not those with IHH. There was no difference between the two groups in target height, the researchers note, suggesting that CDGP was not associated with familial short stature.

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