PREDICTIVE VALUE OF LUTEINIZING-HORMONE-RELEASING HORMONE (LHRH) BOLUS TESTING BEFORE AND AFTER 36-HOUR PULSATILE LHRH ADMINISTRATION IN THE DIFFERENTIAL-DIAGNOSIS OF CONSTITUTIONAL DELAY OF PUBERTY AND MALE HYPOGONADOTROPIC HYPOGONADISM

Intravenous LHRH bolus testing (100 mu g) after 36 h of pulsatile LHRH administration (5 mu g/90 min) preliminary has been reported to allow complete differentiation between constitutional delay of puberty (DP) and hypogonadotropic hypogonadism (HH) in a small group of sexually i mmature patients. So far, these data have never been confirmed. To ass ess the discriminatory power of the test, 33 patients with a presumpti ve diagnosis of either DP (n = 17) or HH (n = 16), confirmed by clinic al follow-up, were studied accordingly. Both groups of patients had si milar mean basal LH and FSH levels (P > 0.10). The mean basal plasma t estosterone level was three times higher in DP than in I-III (4.2 +/- 1.0 vs. 1.4 +/- 0.2 nmol/L, P < 0.001), but there was a wide overlap. In response to the first LHRH bolus test, the mean LH increment was s ignificantly lower in HH than in DP patients (P < 0.001), but, in 44% of the patients, the values overlapped. The FSH increments were simila r in HH and DP. Pulsatile LHRH administration for 36 h similarly incre ased LH levels in HH and DP to values (2.7 +/- 0.4 and 3.8 +/- 0.5, re spectively) slightly higher than before (P < 0.01), but again, not sta tistically significantly different from each other. The mean testoster one levels increased 2-fold in both groups and remained significantly higher in DP than in HH (7.6 +/- 2.1 vs. 2.8 +/- 0.5 nmol/L P < 0.05) . The mean FSH levels after priming also rose, however, to levels sign ificantly higher in HH than in DP (5.2 +/- 0.8 vs. 3.5 +/- 0.4, P < 0 .05). In HH the ratio of FSH to LH almost doubled, whereas it virtuall y remained unchanged in DP. LHRH bolus testing after LHRH priming evok ed a significantly lower LH response in both HH and DP than before pri ming despite only slightly higher baseline LH values. The LH increment in HH was five times lower in HH than in DP. In any of the 16 HH pati ents, the LH increment was greater than or equal to 3 IU/L, whereas in 15 out of 17 DP patients the increase was higher (sensitivity of the test 100%, specificity 88%, and diagnostic efficiency 94% after LHRH p riming against 56%, 94%, and 75% respectively, before LHRH priming. Co nsidering the maximum FSH over LH increments (Delta FSH maxi Delta LH max), this ratio exceeded the arbitrary cut-off point of 0.55 in all 1 6 HH patients, against only 1 out of 17 DP patients (sensitivity 100%, specificity 94%, diagnostic efficiency 97% after LHRH priming against 50%, 100%, and 75% respectively, before LHRH priming). In only 1 of 3 3 patients with HH or DP were both criteria falsely positive. In concl usion, LHRH priming for 36 h increases the discriminatory power of LHR H bolus testing to almost 100%, especially when the ratio Delta FSH ma x/Delta LH max is considered in addition to the LH increment.