Urinary human growth hormone measurement using a highly sensitive sandwich enzyme immunoassay: diagnostic and therapeutic uses in patients with growth hormone deficiency

Normal urinary growth hormone measurement in short-stature early pubertal boys may help to exclude growth hormone deficiency

OBJECTIVE

To determine whether urinary growth hormone (U-GH) measurement is a useful indicator of subsequent growth rate in young boys.

METHODS

We assessed the U-GH concentrations in five early pubertal boys with constitutional short stature (CSS) who were referred to a growth clinic and compared the results with those obtained in normal children and in children with GH deficiency.

RESULTS

In the five early pubertal short-stature boys, the U-GH concentration ranged from 3.7 to 9.7 ng/night and, despite their blunted plasma GH responses to two different pharmacologic tests (peak plasma GH <7 ng/mL), proved to be a useful indicator of their subsequent normal growth rate. The U-GH was 2.2 +/- 0.2 and 4.1 +/- 0.5 ng/night in 38 normal prepubertal and pubertal children, respectively, 2.4 +/- 0.2 ng/night in 13 subjects with CSS, and 1.1 +/- 0.2 ng/night in 16 GH-deficient short-stature children.

CONCLUSION

We may speculate that 24-hour GH secretion and possibly U-GH normalize sooner than do responses to provocative testing as sex steroids appear in early pubertal constitutional short-stature boys. From a practical standpoint, it seems that U-GH values higher than 2.6 ng/night (mean + SE value for subjects with CSS) in such patients may justify postponement of the pharmacologic tests and waiting for growth during the subsequent year.

The impact of gender, puberty and body mass on reference values for urinary growth hormone (GH) excretion in normally growing non-obese and obese children

OBJECTIVE

There is a lack of normal reference data on urinary GH (u-GH) excretion in children. We have investigated the impact of age, gender, pubertal development and body mass on reference values for u-GH excretion in normally growing non-obese and obese children.

STUDY DESIGN

u-GH levels were evaluated in 1153 healthy normal children (aged 5-14) and in 684 obese children (body mass index, BMI: > 75th). u-GH levels (ng/8 h) were determined by ELISA as the mean value of three consecutive first morning voidings.

RESULTS

Reference values (5-95th centile) for u-GH excretion in obese and non-obese children of both sexes are reported. In normal prepubertal children median u-GH levels were relatively stable and superimposable in the two sexes; subsequently, u-GH levels increased, reaching a peak value at 13 years in both sexes. Significant increments (P < 0.0001) in u-GH levels were shown at B2 for females and at G3 for males. A slight decline was evident at 14 years. In obese children, median u-GH concentrations were significantly lower than those recorded in normal children of prepubertal age and at all stages of puberty (except in females at B2), in spite of their comparable normal height. u-GH levels significantly increased at puberty also in obese children, although the pubertal rise was significantly (P < 0.001) lower (1.7-fold in both sexes) than that observed in normal children (2.5-fold in boys and 2.3-fold in girls). A multiple regression analysis showed that both chronological age (beta: 0.20), BMI (beta: - 0.11), gender (beta: - 0.04) and pubertal stage (beta: 0.25) contributed significantly to the physiological variation in u-GH levels (multiple R: 0.44, P < 0.00001).

CONCLUSIONS

This study provides reference values for u-GH in normally growing non-obese and obese children, analysing the impact of gender, puberty and body mass on this parameter. In agreement with previous studies, which demonstrate blunted GH-responses to provocative stimuli and reduced nocturnal GH concentration, obese children have significantly lower u-GH levels than age-matched normal weight children, both before and during puberty.

Low urinary GH levels in normal statured obese children

Urinary GH (u-GH) levels were evaluated in 240 children (age range 5-14 years; 136M, 104F) of normal height (25-90th centile); 165 children were defined as "non-obese" (body mass index (BMI) < 75th centile for their chronological age (CA)) and 75 as "obese" (BMI > 75th). U-GH levels were determined using a two-site enzyme immunometric assay and calculated as the mean obtained from the values of three consecutive first morning voidings; results were expressed as both u-GH concentration (ngl-1) and u-GH excretion (ng per night). Multiple regression analysis revealed that in all children (non-obese and obese) most of the variation in u-GH levels (ngl-1 and ng night-1) was explained by BMI (coefficient: -0.72, p < 0.0001 and coefficient: -0.10, p < 0.001, respectively) and chronological age (coefficient: 1.03, p < 0.01 and coefficient; 0.27, p < 0.001, respectively), whereas sex and pubertal stage did not add significance to the variance. In obese children, mean u-GH concentration and u-GH excretion (per night) levels were significantly lower than those recorded in non-obese children both before and during puberty. A similar trend towards higher u-GH levels at puberty was found in non-obese and obese children. In conclusion, our study shows that u-GH levels are (a) related to CA and BMI in the general population and (b) significantly lower in obese than in non-obese children, in spite of their comparable normal height. The measurement of u-GH excretion in the assessment of children with short stature needs to take into consideration the role of marked ponderal excess, which is associated "per se" with significantly lower u-GH levels.

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.

Screening for growth hormone deficiency using urinary growth hormone measurement

The diagnostic approach in growth hormone deficiency (GHD) is complicated. Two or more provocative tests are essential for definitive diagnosis of GHD. However, such testing cannot be carried out routinely on all subjects with short stature because of the need for hospitalization and blood sampling. A simple screening method for GHD would be of great value. Human growth hormone (hGH) levels were measured in the early morning urine of 192 children aged 7-15 years with height 2.0 s.d. below the mean for their ages. Sixty-eight subjects were selected because they showed a urinary hGH level < 10 ng/g creatinine. They were further examined in terms of bone age and plasma insulin-like growth factor (IGF-I) levels. In 30 subjects, the ratio of bone age: chronological age was < 0.8 and/or plasma IGF-I level was < 0.7 U/mL. Finally 24 of these subjects were examined with provocative tests and other endocrinological tests. Eleven subjects proved to have poor growth hormone secretion and one subject was diagnosed as having Turner syndrome. In conclusion, 11 patients with GHD were diagnosed from 192 children with short stature using urinary hGH measurement as the first screening method. These findings suggests that urinary hGH measurement could be a useful and simple method for detecting GHD.