Urinary growth hormone and insulin-like growth factor I. Effects of growth-hormone injection schedule

Relationship between serum and urinary insulin-like growth factor-I through childhood and adolescence: their use in the assessment of disordered growth

OBJECTIVE

Serum insulin-like growth factor-I (sIGF-I) measurement as an index of growth hormone status has become a common test in the investigation of disordered growth. IGF-I may also be measured in the urine. The aims of this study were to investigate the correlation between serum and urinary IGF-I in normal children and compare their use in the evaluation of growth disorders.

DESIGN

Normal ranges for serum and urinary IGF-I were devised from a cross-sectional study of normal schoolchildren. These were then used to assess the sensitivity and specificity of serum and urinary IGF-I in the diagnosis of childhood GH deficiency.

PATIENTS

A cohort of 333 (M = 156, F = 177) healthy schoolchildren aged 5-19 years were recruited and data previously collected from 22 growth hormone deficient (GHD) and 47 short normal (SN) children were compared with those of the normal children.

MEASUREMENTS

Height, weight and pubertal status were assessed in all children. Serum IGF-I (sIGF-I) (n = 305) and total amount of urinary IGF-I excreted overnight (TuIGF-I) (n = 205) were measured by RIA using excess IGF-II to block the interference of IGFBPs.

RESULTS

Serum IGF-I was loge transformed and overall levels (geometric mean +/- 1 tolerance factor) were higher in females than males (F: 569 (329, 985) micrograms/l; M: 398 (227, 696) micrograms/l). LogeIGF-I correlated with age (F: r = +0.76, P < 0.001, M: r = +0.71, P < 0.001) and was significantly affected by both sex and Tanner stage of puberty (TS) (both P < 0.001). The distribution of TuIGF-I was normalized by performing a square root transformation (square root of TuIGF-I). square root of TuIGF-I was correlated with age (F: r = +0.36, P < 0.001; M: r = +0.5, P < 0.001) and was significantly affected by TS (P < 0.001). In both sexes there was a highly significant correlation between logeIGF-I and square root of TuIGF-I (F: r = +0.39, P < 0.001; M: r = +0.41, P < 0.001). Using the third centile of our normal ranges as a cut off to identify GHD, sIGF-I had a sensitivity of 82% and specificity of 62%, whereas TuIGF-I had a sensitivity of 18% and specificity of 79%.

CONCLUSIONS

This study demonstrates that although urinary IGF-I has no place in the diagnosis of growth disorders, in normal children there is a highly significant relationship between serum and urinary IGF-I with levels of each changing in a similar manner through childhood and adolescence. Thus, TuIGF-I could be used as a valid surrogate for sIGF-I in the physiological assessment of the relationship between IGF-I status and the normal growth process.

Current methods for the measurement of growth hormone in urine

Since the development of sensitive immunoassay procedures for the measurement of GH in urine, a urinary GH determination has been proposed as an alternative way of assessing pituitary GH secretion. Whilst studies on the clinical application of these assays have been difficult to correlate, for the reasons described, it is clear that an estimation of urinary GH has a useful role in clinical and physiological studies in both children and adults.