Urinary IGF-I measurement and its clinical application

Area of Science:

• Endocrinology
• Biochemistry
• Urine analysis

Background:

• Insulin-like growth factor I (IGF-I) plays a crucial role in growth and metabolism.
• IGF-I exists in various forms, including free and bound to binding proteins.
• Urinary excretion of biomarkers is increasingly recognized as a valuable diagnostic tool.

Purpose of the Study:

• To investigate the presence and characteristics of IGF-I in human urine.
• To assess the correlation between urinary IGF-I levels and plasma IGF-I and growth hormone (GH) concentrations.
• To evaluate the potential clinical utility of urinary IGF-I as an indicator of GH secretion status.

Main Methods:

• Radioimmunoassay (RIA) was used to quantify IGF-I in urine after Sep-Pak C18 cartridge extraction, specifically measuring the free form.
• 24-hour urinary IGF-I excretion was measured in hypopituitary and short normal children.
• Plasma IGF-I and GH levels were measured concurrently.

Main Results:

• Immunoreactive and receptor-reactive IGF-I was detected in human urine, with 30% in free form and 70% as a high molecular weight complex.
• 24-hour urinary IGF-I excretion correlated with plasma IGF-I and mean 24-hour plasma GH concentration.
• Mean IGF-I levels in single urine samples differentiated between acromegaly, normal subjects, and hypopituitarism, though with some overlap.

Conclusions:

• Urinary IGF-I levels reflect the growth hormone (GH) secretion state.
• While urinary IGF-I shows promise as a biomarker, its clinical application in assessing GH status may be limited due to variability and overlap in individual values.