Measurement of nocturnal urinary growth hormone values

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.

Urinary growth hormone determination in prepubertal children using a modification of a commercial kit designed for determination of growth hormone in serum

The aims of the present study were to validate a method for the determination of growth hormone (GH) in urine using a commercial immunoradiometric kit designed for serum GH determination and to derive a reference range for healthy prepubertal school children. The urinary GH concentrations in prepubertal children with short stature undergoing provocative GH tests were also investigated. Intra- and interassay coefficients of variance were 5.9% and 4.3% respectively and the mean detection limit of the assay, calculated as +2SD from the blank values was 0.2 microU l-1. Significant differences in the levels of urinary GH were observed between different collection times in the same individual. The urinary GH excretion in the normal school children was 8.2 +/- 4.5 microU night-1 (range 1.3-19.6 microU night-1). The urinary GH excretion in the short healthy children was not significantly lower than that of the healthy school children. No correlation was found between height, growth velocity or body-mass index and the overnight excretion of GH in the normal school children.

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.

Urinary growth hormone excretion in the assessment of children with disorders of growth

OBJECTIVE

We wished to evaluate the use of urinary GH measurements when compared to conventional GH provocation tests in the assessment of short children.

DESIGN

Children presenting for the first time to a regional growth clinic were assessed clinically by one observer. Investigations comprising standard GH provocation tests and measurement of urinary GH were undertaken to exclude GH deficiency.

PATIENTS

Fifty-eight children aged 5.8-16 years were enrolled. Ten were diagnosed on clinical assessment as GH deficient, 43 had delayed growth and/or familial short stature, and five had idiopathic short stature; the 48 children in the last two groups were defined as short normal.

MEASUREMENTS

GH secretion was evaluated by two standard provocation tests and by the measurement of GH in five overnight urine collections. A normal peak GH concentration was defined as > 16 mU/l. The values for urinary GH excretion were compared to normal ranges (+/- 2 standard deviations from the mean), established in healthy schoolchildren of normal stature.

RESULTS

All children considered GH deficient on clinical grounds had low peak GH concentrations on provocation tests, while 8/10 had low values of urinary GH excretion. All short normal children with normal peak GH concentrations (n = 36) on provocation tests and 11/12 children with low peak GH concentrations had urinary GH excretion within the normal range. There was therefore a significant difference in the classification of 'normal' GH secretion in the two tests. If the clinical diagnosis was used as the standard by which GH tests were judged, the predictive value of a positive urinary GH test in the diagnosis of GH deficiency was 89% compared with 45% for GH provocation tests.

Analysis of trough serum growth hormone concentrations: comparison of an immunoradiometric assay and a sensitive ELISA for growth hormone

OBJECTIVES

We compared a sensitive assay for GH (ELISA) with a conventional immunoradiometric (IRMA) assay with particular reference to the oscillatory activity detected by Fourier transformation and the estimation of trough concentrations using occupancy analysis.

DESIGN

Eight healthy adult male volunteers underwent 24-hour profiles during which samples were drawn at 20-minute intervals. Samples were analysed by an ELISA and an IRMA system.

MEASUREMENTS

The 24-hour serum GH concentration profiles were subjected to Fourier transformation and to occupancy analysis.

RESULTS

No additional GH periodicities could be determined in the ELISA data other than the well documented 180-200-minute periodicity. Median observed concentrations (OC) at 5% occupancy were 0.035 mU/l (range 0.004-0.22) for the ELISA and 0.035 mU/l (range 0.001-0.50) for the IRMA. For all OC parameters, 5, 50 and 95%, there was a good correlation between the ELISA and IRMA systems. The mean difference (bias) between the ELISA and IRMA were -0.05, -0.28 and -1.40 mU/l at OC values of 5, 50 and 95% respectively and the standard deviations of the difference at the same OC values were 0.10, 0.50 and 1.61 mU/l.

CONCLUSION

Although there is a qualitative improvement on visual inspection of individual 24-hour serum GH profiles obtained using the ELISA system, there is little additional information gained in terms of pulse periodicity or occupancy analysis.

Urinary excretion of human growth hormone in children with short stature: correlation with pituitary secretion of human growth hormone

Thirty-five children with short-stature underwent insulin-loading and sleep tests for assessment of secretion of human growth hormone. Correlations between the levels of human growth hormone in the serum and urine during the tests were examined to elucidate the clinical significance of urinary human growth hormone levels in short children. The concentration and total amount of human growth hormone in the urine correlated significantly with the peak concentration of serum human growth hormone (r = 0.81, p less than 0.001 and r = 0.80, p less than 0.001, respectively) and the integrated concentration of human growth hormone (r = 0.85, p less than 0.001 and r = 0.85, p less than 0.001, respectively) in the insulin-loading test. The concentration and total amount of human growth hormone in the morning urine also correlated significantly with the peak concentration of serum human growth hormone (r = 0.80, p less than 0.001 and r = 0.70, p less than 0.001, respectively) and the integrated concentration of serum human growth hormone (r = 0.80, p less than 0.001 and r = 0.72, p less than 0.001, respectively) in the sleep test. The concentration or total amount of human growth hormone in the urine differed significantly among children with human growth hormone deficiency, those with nonendocrine short stature, and those with normal stature (p less than 0.05). These data suggest that measurement of human growth hormone in the urine may be used to assess secretion of human growth hormone, serving as a screening test for human growth hormone deficiency in children.

The assay of urinary growth hormone in normal and acromegalic adults

OBJECTIVES

To establish a normal range for urinary growth hormone in adults and to investigate the urinary growth hormone levels in patients with acromegaly, comparing these with the serum growth hormone results of a glucose tolerance test. We also studied the molecular identity of the growth hormone recognized by our assay method.

DESIGN

Overnight urine samples and, in some cases, timed urine samples taken during the day were obtained from healthy volunteers and acromegalic patients. A standard glucose tolerance test with serum growth hormone measurements was performed on the acromegalic patients.

PATIENTS

One hundred and thirty-five normal adults and 33 acromegalic patients were studied.

MEASUREMENTS

Urinary growth hormone was measured using a sensitive and precise assay developed previously.

RESULTS

In healthy volunteers overnight urinary growth hormone values fell gradually with increasing age, but there was no significant difference between men and women in any decade or between smokers and non-smokers. Sexual intercourse had no detectable effect on the values, but there was a large increase following strenuous exercise. Studies of the diurnal patterns in normal and abnormal adults suggested that it might be possible to diagnose acromegaly on a random urine sample. Gel filtration studies on a urine sample from an acromegalic patient showed a single peak of molecular weight 22,000. Using overnight collections there was clear discrimination between the values given by the normal adults and the acromegalic patients and an excellent correlation between urinary growth hormone levels in acromegalic patients and the mean serum growth hormone in a glucose tolerance test.

CONCLUSIONS

In contrast to some other groups we conclude that urinary growth hormone provides a useful, non-invasive screening test for acromegaly, but this conclusion depends crucially on the assay being sensitive and precise at low values.

Urinary growth hormone excretion during puberty in type 1 (insulin-dependent) diabetes mellitus

The excretion of urinary growth hormone was measured by a highly sensitive direct immunoradiometric assay in a cross-sectional study during puberty in 70 children with Type 1 (insulin-dependent) diabetes mellitus and 94 normal children. In normal children (n = 24) and diabetic children (n = 17) overnight urinary growth hormone excretion correlated significantly with the mean overnight plasma concentration (r = 0.70, p less than 0.001, and r = 0.70, p less than 0.001), indicating that urinary GH excretion reflects the circulating endogenous GH level. Overnight urinary growth hormone excretion increased during puberty. In normal and in diabetic children there was a peak in boys at genital stage 4 (both p less than 0.01), and in girls at breast stage 2 (both p less than 0.02). The diabetic children excreted more urinary growth hormone than the normal children at every pubertal stage. Excretion of albumin, retinol binding protein and N-acetyl-beta-D-glucosaminidase was measured in urine from 38 diabetic children. Urinary growth hormone correlated weakly with urinary albumin (r = 0.49, p less than 0.01), retinol binding protein (r = 0.42, p less than 0.01), and N-acetyl-beta-D-glucosaminidase (r = 0.43, p less than 0.01). Urinary GH excretion was not related to blood glucose control (HbA1) in boys (n = 31) or girls (n = 39). The measurement of urinary growth hormone provides an assessment of endogenous growth hormone during puberty in normal and diabetic children. However, caution must be exercised in interpreting urinary growth hormone data from diabetic patients with increased excretion of albumin and retinol binding protein.

Overnight urinary growth hormone measurement in the diagnosis of acromegaly

Several studies report higher urinary GH excretion in acromegalic patients compared to control subjects. We investigated the diagnostic potential of overnight urinary GH excretion in acromegaly, using a recently developed enzyme-linked immunosorbent assay. Overnight urine samples were obtained from 117 control subjects and nine patients with untreated acromegaly. GH excretion was higher in acromegalic patients compared to control subjects, with geometric mean total overnight values of 46.35 and 5.73 microU respectively. The range for total overnight urinary GH in control subjects was 0.75-21.75 microU and two of the nine patients with untreated acromegaly had GH measurements within this range. Urinary GH measurements were corrected using predictive clinical variables but this resulted in minimal improvement in discrimination between control subjects and acromegalic patients. Lack of complete discrimination between control subjects and acromegalic patients limits the usefulness of a single overnight urinary GH measurement as a screening test for acromegaly.