Basal follicle-stimulating hormone and peak gonadotropin levels after gonadotropin-releasing hormone infusion show high diagnostic accuracy in boys with suspicion of hypogonadotropic hypogonadism

CONTEXT

Differential diagnosis between hypogonadotropic hypogonadism (HH) and constitutional delay of puberty in boys is challenging. Most tests use an acute GnRH stimulus, allowing only the release of previously synthesized gonadotropins. A constant GnRH infusion, inducing de novo gonadotropin synthesis, may allow a better discrimination.

OBJECTIVE

We evaluated the diagnostic accuracy of basal and peak gonadotropins after GnRH infusion, measured by ultrasensitive assays, to confirm the diagnosis in boys with suspected HH.

DESIGN AND SETTING

We conducted a validation study following Standards for Reporting of Diagnostic Accuracy criteria at a tertiary public hospital.

PATIENTS AND METHODS

A GnRH i.v. infusion test was performed in 32 boys. LH and FSH were determined by immunofluorometric assay at 0-120 min. DIAGNOSIS ASCERTAINMENT: The following diagnoses were ascertained: complete HH (n = 19; testes < 4 ml at 18 yr), partial HH (n = 6; testes enlargement remained arrested for > or = 1 yr or did not reach 15 ml), and constitutional delay of puberty (n = 7; testes > or = 15 ml at 18 yr).

MAIN OUTCOME MEASURES

Sensitivity, specificity, positive and negative predictive values, and diagnostic efficiency were assessed.

RESULTS

Basal FSH less than 1.2 IU/liter confirmed HH with specificity of 1.00 (95% confidence interval = 0.59-1.00), rendering GnRH infusion unnecessary. In patients with basal FSH of at least 1.2 IU/liter, the coexistence of peak FSH less than 4.6 IU/liter and peak LH less than 5.8 IU/liter after GnRH infusion had high specificity (1.00; 95% confidence interval = 0.59-1.00) and diagnostic efficiency (76.9%) for HH.

CONCLUSIONS

Basal FSH less than 1.2 IU/liter confirms HH, which precludes from further testing, reducing patient discomfort and healthcare system costs. In patients with basal FSH of at least 1.2 IU/liter, a GnRH infusion test has a high diagnostic efficiency.

Basal ultrasensitive LH assay: a useful tool in the early diagnosis of male pubertal delay?

The aim of this study was to evaluate the usefulness of basal measurements of gonadotropins in distinguishing between constitutionally delayed puberty (DP) and hypogonadotropic hypogonadism (HH), comparing its diagnostic efficiency with that of the dynamic GnRH infusion test (0.83 microg/min during 120 min). We studied 20 males, chronological age (CA) 14-18 years, with a final diagnosis of DP (n = 8), partial HH (n = 5) and complete HH (n = 7), confirmed by follow-up. We also evaluated basal samples of ultrasensitive LH and FSH in 117 healthy control males (CA 2-19 yr), classified according to Tanner stage. In the control group, ROC plot analysis showed a cutoff to differentiate prepuberty from puberty of 0.65 IU/l for LH (sensitivity: 91%, specificity: 98%). Differences were found (p < 0.05) in basal LH and in maximal responses to GnRH in complete HH in relation to DP and partial HH. The diagnostic efficiency of the GnRH infusion test was 85%. For basal LH, a cut-off limit of 0.65 IU/l showed a diagnostic efficiency of 85% for complete HH and 100% for partial HH and DP. We conclude that, in our experience, basal LH levels above 0.65 IU/l measured by ultrasensitive assay would rule out a complete deficiency. It was not possible to differentiate DP from partial HH, either in basal samples or with the infusion test.