Bioactive LH: a test to discriminate true precocious puberty from premature thelarche and adrenarche.

Since luteinizing hormone levels by radioimmunoassay (I-LH) have rarely been useful in distinguishing true isosexual precocity from other less serious disorders of puberty, we have studied bioassayable B-LH in 17 prepubertal girls, seven girls with premature adrenarche, 12 girls with premature thelarche, and six girls with true isosexual precocity. The I-LH levels were three times higher in the girls with true precocious puberty than in the other groups but there was overlap between those with premature thelarche and true precocious puberty. The B-LH levels were 16 times higher in the girls with isosexual precocity than in the others, and there was no overlap. We conclude that B-LH better discriminates between true isosexual precocity and other disorders of puberty and may be a very useful laboratory test for the early diagnosis of true precocious puberty.