Urinary IGF-I measurement and its clinical application

Immunoreactive and receptor-reactive IGF-I was found to be present in human urine; 30% of the IGF-I immunoreactivity in urine was in its free form and the remainder was a high molecular weight form (approximately 40,000 MW). Urinary IGF-I was quantified by radioimmunoassay after extraction by Sep-Pak C18 cartridge, a method that measures only the free form of IGF-I. Daily (24-hour) urinary IGF-I excretion was measured in 3 hypopituitary children and 16 short normal children. The IGF-I level in the 24-hour urine samples correlated with the plasma IGF-I level and the mean 24-hour plasma GH concentration. The mean 24-hour plasma GH concentration, however, correlated better with the GH level in the 24-hour urine samples and the plasma IGF-I level than with the urinary IGF-I value. The mean IGF-I levels in single urine samples from normal subjects lay between those from patients with acromegaly (which were high) and those from patients with hypopituitarism (which were low). There were overlaps, however, in individual values between the normal and hypopituitary patients. These data indicate that urinary IGF-I values are altered by the GH secretion state, though the clinical application of urinary IGF-I measurement may be limited.