The reference value ranges established in this study reflect significant differences between genders. It is possible that these reference ranges may be generalizable to adults living in Thailand. The findings of this study emphasize the importance of establishing specific hematologic reference values for specific populations.

Background: GnRH stimulation test is the gold standard for the diagnosis of central precocious puberty (CPP). However, it is invasive and costly. Previous studies showed that increased urinary gonadotropins (Gn) level in first morning voided (FMV) urine reflected the integration of elevated nocturnal Gn secretions. Therefore, it could be used to diagnose CPP. Nevertheless, its cutoff value for diagnosis of CPP is limited. Objective: To determine the association of Gn levels in FMV urine and serum during pubertal development and establish cutoff value of FMV urinary Gn as an alternative noninvasive method for diagnosis of CPP in girls. Methods: Sixty-one girls who had breast development before 8 years of age with sign of rapid pubertal progression (advanced bone age and/or increased height velocity) underwent subcutaneous GnRH agonist test. FMV urinary Gn were also collected on the same day. Both serum and urinary Gn levels were measured using electrochemiluminescence immunoassay (ECLIA) technique. The definite diagnosis of CPP is based on stimulated serum LH > 5 IU/L. FMV urinary Gn were compared between CPP and premature thelarche (PT) groups. The correlation between serum and urinary Gn were assessed and the cutoff value of urinary Gn to diagnose CPP was established. FMV urinary Gn of 480 Thai school girls (control) were also collected to determine the reference values according to their breast Tanner (BT) stages. Results: FMV ULH level in girls with CPP was significantly higher than that of PT (2.46 VS 0.8 IU/L; median, P <0.001). However, the level of ULH in PT group was not different from control group with BT1. FMV ULH and ULH: UFSH were well correlated with basal serum LH (r=0.63 and 0.73, respectively, Ps<0.001) and peak serum LH (r=0.44 and 0.54, respectively, Ps<0.001). Base on receiver operating characteristics analysis, basal serum LH was the best parameter to differentiate CPP from PT (area under the curve 0.797–0.926). ULH levels at ≥ 1.13 IU/L and ≥ 1.52 provide optimal sensitivity (72.3 and 68.1 %, respectively) and specificity (85.7 and 100 %, respectively). Combined ULH level ≥ 1.13 IU/L with ULH: UFSH ≥ 0.17 increased specificity from 85.7 to 92.9 % for predicting a positive GnRH agonist test. (peak LH ≥ 5 IU/L) Conclusions: First morning voided urinary Gn levels measurement is a highly potential method for the diagnosis of CPP in girls due to its good correlation with GnRH agonist test. Further study in a larger number of patients with close monitoring of clinical outcome is required before recommending as a standard investigation in CPP.