Preanalytical factors affecting RIA measurement of plasma kisspeptin.

Kisspeptins are peptide products of the KiSS-1 metastasis-suppressor (KISS1) gene and the natural ligands of the G-protein– coupled receptor GPR54. KISS1 was initially investigated as an antimetastasis gene. More recent studies have demonstrated that the kisspeptins are potent stimulators of the hypothalamo-pituitarygonadal axis. Mice and humans with defective kisspeptin signaling show hypogonadotrophic hypogonadism and impaired sexual development (1, 2 ). Plasma kisspeptin concentrations are 2 pmol/L in men and nonpregnant women. KiSS-1 mRNA is highly expressed in the placenta, and plasma kisspeptin concentrations increase dramatically, to thousands of picomoles per liter, during pregnancy (3). In addition, plasma kisspeptin is increased in women with gestational trophoblastic tumors, thus raising the possibility of measuring plasma kisspeptin as a novel tumor marker (4). Previous studies that have measured plasma kisspeptin in women during pregnancy have found significantly different concentrations of circulating kisspeptin (3, 4) that may be attributable to differences in preanalytical variables, such as collection tube type, processing times, and storage conditions. Use of a standardized sample collection method for the mea-