SUN-265 Performance of Basal and GnRH Analog-Stimulated LH Levels Assessed by an Electrochemiluminescence Assay in Girls with Central Precocious Puberty

Background: The laboratory evaluation of patients with precocious puberty is useful to differentiate central precocious puberty (CPP) from isolated thelarche (IPT) and peripheral precocious puberty (PPP). Ultrasensitive immunoassays, such as electrochemiluminescence (ECLIA), improved sensitivity and specificity of basal and GnRH-stimulated LH levels to establish the differential diagnosis among these conditions. Aim: To establish the diagnostic value of basal and GnRHa-stimulated LH values and basal estradiol assessed by ECLIA in pubertal disorders. Patients and Methods: We included 38 girls with pubertal disorders (28 CPP, 8 IPT, and 2 PPP). Their medical records were systematically revised. Clinical and hormonal data [basal and GnRH analog -stimulated LH levels (2 hs after leuprorrelin 3.75 mg) and basal estradiol] were analyzed. Gonadotropins and estradiol levels were assessed by ECLIA (Roche, Cobas e 6000). The functional sensitivity of the assays was 0.15 IU/L for LH, FSH 0.6 IU/L for FSH and 17 pg/mL for estradiol. Basal gonadotropins and estradiol were also assessed in a control group composed by 16 prepubertal and 19 pubertal girls. The cutoff values for basal and GnRH analog- stimulated LH for diagnosis of CPP was set at < 0.3 IU/L and 8 IU/L, respectively (1). Results: The mean age of girl with CPP, IPT, and PPP at the first clinical visit was 8 ± 0.9yr (5.25- 9.6 yr), 4.25± 2.6 (0.7-7.8 yr), and 5.12±2.9 (3.1 -7.1 yr), respectively. All CPP girls presented breast development ranging from B2 to B5, whereas IPT group B2-B4 and PPP group (B2). Pubarche was presented in 86% of girls with CPP (PH 2- PH 5). Only one girl in IPT group also presented pubarche (PH3), associated to zinc oxide cream use and none in PPP group presented pubarche. The mean basal LH was 3.4 ± 1.6 (<0.1- 8.6 IU/L), 0.15 ± 0.03 (< 0.15-0.2 IU/L), and <0.15 IU/L for CPP, IPT, and PPP, respectively. In CPP group, GnRHa- stimulated LH and basal estradiol levels were 6 ± 2.8 (4-61.4 IU/L) and 21 ± 17 (<17- 90 pg/ml), respectively. The sensitivity and specificity of basal and GnRHa-stimulated LH values for diagnosis of CPP was 64.7 % and 100%, respectively. However, the cutoff of 5 IU/L for GnRHa-stimulated LH improved sensitivity to 87.5% but with lower specificity of 67%. Estradiol was undetectable (<17 pg/ml) in 48% girls with CPP. In the IPT and PPP groups, basal LH <0.3 IU/L was detected in all patients. In the control group, all but one prepubertal girl had basal LH <0.15 IU/L. In addition, basal estradiol > 17 pg/ml was present in two girls from control prepubertal group. In the control pubertal group (B3-B4), mean basal LH was 4.2± 2.3 (<015- 8.8 IU/L) and basal estradiol was 61 ± 34 (<17-135pg/mL). Conclusion: The diagnostic value of basal and GnRH-stimulated LH levels assessed by ECLIA to diagnosis CPP is limited and must be interpreted together with clinical data. Reference: (1) Freire AV et al, Clin Endocrinol (Oxf), 2013.