Urinary growth hormone excretion as a screening test for growth hormone deficiency

Development and evaluation of a direct immunofluorimetric assay for urinary growth hormone

We describe a two-site immunofluorimetric assay for urinary growth hormone that is resistant to interference from a wide range of urinary constituents and therefore eliminates the need for sample pre-treatment. A microtitre plate format is used with specific orientation of capture antibody on a polystyrene surface carrying a hydrazide group. Europium-labelled F(ab)2 is the fluorophore and time-resolved fluorimetry with co-fluorescence enhancement the signal detection system. Inter-assay precision was 11.3% at 5.2 ng/L and 10.3% at 44.3 ng/L, minimum detection limit (22% coefficient of variation, CV) was < 1.0 ng/L, working range (< 10% CV) was 0-100 ng/L and quantitative recovery and good parallelism were demonstrated. This convenient and sensitive assay is suitable for the routine measurement of human growth hormone (hGH) in urine.

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.

Effects of inhaled corticosteroids and inhaled cromolyn sodium on urinary growth hormone excretion in asthmatic children

Over the past few years there has been an increasing awareness that asthma is a chronic inflammatory airways disease. The current therapeutic strategies for treating asthma focus on suppressing the inflammatory process by using cromones or inhaled corticosteroids (ICS). The beneficial effects of ICS in asthma are now well known, but its detrimental effect on linear growth remains a controversial issue. The aim of this open label, nonrandomized, cross-sectional, one-time study was to determine the influence of these drugs on urinary growth hormone (U-GH) levels in prepubertal asthmatic children. U-GH levels were measured in 47 prepubertal asthmatic children who had been treated for at least 6 months with either ICS (beclomethasone or budesonide at a mean daily dose of 360 microg) or with 80 mg daily dose of cromolyn sodium (CrS). There were also nine healthy children who served as a control. These three groups of children were matched for age and gender ratio. The mean level of U-GH in the CrS-treated group was 2.94 +/- 0.96 ng/night; this was significantly higher compared to the mean level of the ICS-treated group (1.99 +/- 0.83 ng/night; P < 0.001) and to the mean level of the control group (1.98 +/- 0.39 ng/night; P < 0.006). There was no significant difference between the mean level of U-GH in the group treated by ICS and the controls (P < 0.9). These results show that the mean levels of U-GH secretion of the children who were treated by CrS for 6 months was significantly increased, compared to the mean U-GH level of the ICS-treated group and the controls. The mean U-GH levels in the last two groups showed no statistically significant difference.

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.

The reproducibility of urinary growth hormone measurement in children undergoing adenotonsillectomy: a pilot study

The reproducibility of urinary growth hormone levels in normal children and in children undergoing adenotonsillar surgery was investigated. Thirty normal children and 32 children pre- and post-adenotonsillectomy had overnight urinary growth hormone levels measured on two consecutive nights using the technique of immunoradiometric assay. There was no significant difference when levels in each of these groups were compared. Therefore, the results were pooled (n = 94) and the correlation coefficient comparing levels obtained on the first and the second consecutive nights sample was calculated, r = 0.644 (P < 0.001). This work suggests that studies of urinary growth hormone levels in children give reproducible results. Further investigation of this technique as a screening or diagnostic procedure in the clinical setting can now be more widely evaluated.

Assessment of GH status in adults with GH deficiency using serum growth hormone, serum insulin-like growth factor-I and urinary growth hormone excretion

OBJECTIVES

The benefits of treating adults with GH deficiency are now well recognized although the criteria for deciding which patients to treat are still not clear. At present the 'gold standard' is the insulin stress test (IST) which is unpleasant and potentially dangerous, particularly in patients with hypopituitarism. The aim of this study was to determine whether alternative methods of assessing GH status are reliable in predicting GH deficiency.

SUBJECTS AND METHODS

Forty-four patients with unequivocal GH deficiency (peak IST < 2 mU/l) and 17 with partial deficiency (peak IST 2-10 mU/l) were studied. Each patient was assessed clinically with respect to the number of other pituitary axes affected and biochemically with an estimate of urinary GH excretion (uGH) and serum IGF-I. These markers were then related to GH status as defined by insulin stress testing.

MEASUREMENTS

Insulin stress tests were performed using 0.1 units/kg i.v. and accepted with a blood glucose < 2 mmol/l. Serum GH and IGF-I were measured by radioimmunoassay whilst uGH was estimated by an immunoradiometric assay using commercially available reagents. uGH was estimated from the mean of two overnight urine collections which consisted of all urine passed from last voiding through to the first morning sample.

RESULTS

The presence of unequivocal GH deficiency (peak IST < 2 mU/l) was predictable if 2 or more other pituitary axes were affected (90%). uGH declined significantly with the level of peak IST response (P < 0.001) and almost so with the number of other deficient hypothalamic-pituitary axes affected (P = 0.057). Thus, uGH accurately reflected GH status and showed good separation from normal controls in patients less than 40 years (specificity 79%) and between 40 and 60 years (specificity 67%). Above this age the method is less specific (36%). Patients excreted significantly less GH than controls in all three age groups (P < 0.01). Subnormal levels of IGF-I were strongly predictive of unequivocal GH deficiency (91% with subnormal IGF-I have a peak IST GH < 2 mU/l) although a normal value does not reliably exclude the diagnosis.

CONCLUSIONS

A diagnosis of adult GH deficiency can be reliably made without the need for an insulin stress test by using a combination of low urinary GH excretion, subnormal IGF-I levels and clinical assessment with regard to the number of other pituitary axes affected.

Screening test for growth hormone deficiency: usefulness of L-dopa-propranolol provocative test

This is a retrospective review of 185 short children who were tested for growth hormone (GH) secretion using the L-dopa-propranolol provocative test. One hundred and thirty-three children were deemed to have passed the screening test when a GH concentration of greater than 15 miu/L was elicited after stimulation. Fifty-two failed the screening test, of which 33 were diagnosed as having growth hormone deficiency (GHD) when they had inadequate growth hormone response to insulin-induced hypoglycaemia. The other 19 were low-responders since they showed adequate GH response to insulin tolerance test (ITT). The low-responder rate to L-dopa-propranolol provocative test among short children who are not GH deficient was 12.5%. The low cost of L-dopa and propranolol, the simplicity and safety of the test, and the acceptable rate of low-responders make the test an effective screening test for GHD.

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.

Apparent growth hormone levels in plasma and urine. Methodological "artefacts"

Urinary growth hormone reflects plasma levels, if a normal renal function is assured. It offers the advantages of easy repetition over prolonged periods of time. It is an easy tool to assess physiological and pathophysiological aspects of the "amount" of growth hormone secreted in a given clinical situation. It can be used to control therapy and reassess the "growth hormone status" at any time during a treatment period. It cannot, however, replace the assessment of responses of the system to a given stimulus and will not reflect the pulsatility of plasma 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.

Urinary growth hormone measurements in children with renal insufficiency

It has been reported that intrinsic renal factors could affect urinary growth hormone (UGH) measurements. We compared UGH excretion in 21 children aged 4-16 years, with various degrees of renal insufficiency, with that in 10 control subjects aged 5-13 years. We found 100- to 1000-fold elevations in UGH in children with plasma creatinine concentrations > 120 mumol/L (Group A) compared with patients with plasma creatinine concentrations < 120 mumol/L (Group B) and control subjects. UGH excretion (microU) in the three groups was as follows: group A 804-8556 (median 2649); group B 1.0-85 (median 7.5); and controls 2.6-7.3 (median 4.0). Elevated urinary beta 2-microglobulin levels (microgram) were also observed in group A patients: 875-15,400 (median 11,637) as compared with group B, 1.0-104 (median 32) and controls, 3-18.7 (median 8.0). There was no significant difference in albumin excretion between groups A and B through six patients in group B with nephrotic syndrome (NS) excreted significantly more albumin (P < 0.05) than the other 15 patients investigated. Our data show that abnormalities of renal function have a profound effect on growth hormone excretion and we suggest proximal tubular dysfunction as the causative factor. We conclude that UGH measurements do not provide a reliable means of assessment of hypothalamo-pituitary function in patients with renal insufficiency.

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.

Overnight urine growth hormone, cortisol and adenosine 3' 5' cyclic monophosphate excretion in children with chronic asthma treated with inhaled beclomethasone dipropionate

Overnight urine samples were obtained from 34 asthmatic children, 24 of whom were receiving inhaled beclomethasone dipropionate (BDP), and 30 controls. The urine volume of the children receiving inhaled steroids was significantly greater than that of the other asthmatic children and of the controls (P < 0.05). Urine growth hormone was within the normal range for all of the subjects and there was no demonstrable relationship between urine growth hormone and height or height standard deviation score. Urine steroid output was significantly reduced in the BDP receiving group when the results were expressed in U l-1 but there was no difference between the groups when the results were expressed per specimen. Urine adenosine 3' 5' cyclic monophosphate (cAMP) results were similar for all groups. We conclude that use of BDP increases overnight urine volume but, in our study, does not appear to influence the output of urine cortisol. Urine free cortisol measurements may not be a very sensitive tool for the detection of small changes in endogenous steroid production. The use of BDP does not adversely affect the output of urine growth hormone.

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.

Urinary growth hormone excretion as measured by a sensitive immunochemiluminometric assay

A sensitive immunochemiluminometric assay with a detection limit of 1.1 microU/L was developed for the measurement of urinary growth hormone (UGH). The assay was shown to be specific and precise. There was a good correlation between serum growth hormone (GH) and UGH concentrations in 20 patients with acromegaly and six volunteers following an intravenous injection of recombinant GH. We concluded therefore that UGH measurements appear to provide a satisfactory index of GH secretion. The use of the assay in the investigation of growth disorders was assessed. We studied 11 pre-pubertal children, six of normal stature, and five of short stature, over a 6-month period. Sequential fortnightly measurements of UGH were carried out and height velocity was determined. The children of short stature grew at a slower rate and excreted less GH than the children of normal stature. However, we observed considerable within-individual variability in GH excretion in both groups (CV 22-98%). We therefore recommend that sequential UGH analyses should be carried out and the results interpreted in conjunction with growth measurements. However, further investigations into the renal handling of GH are needed to establish optimum sampling regimes.

Diagnosis of growth hormone deficiency

Many ways of evaluating the physiological state of hGH secretion exist, some of which have been touched upon and none of which has as yet proven infallible. Apart from important clinical features like history, physical data and growth rate, the diagnosis of altered pituitary function is based on tests and their interpretation. The physician responsible has to be informed on their effectiveness and pitfalls. Results should be interpreted in relation to developmental age (bone age) rather than chronological age. Research is under way to try to facilitate the diagnosis of varying degrees of alterations of hGH secretion. Reliability in predicting the effect of therapy with hGH is the ultimate aim in order to prevent unnecessary cost and disappointment for the patients. With the help of doctors involved in child care, such as physicians at kindergarten or school, it should be possible to start the slow process of investigating growth disorders at an early age.

Relationship between urinary and serum growth hormone and pubertal status

Urinary growth hormone (uGH) excretion and serum growth hormone concentrations have been compared in three groups of children. Group 1 consisted of 21 children who had had cranial irradiation as part of their treatment for acute lymphoblastic leukaemia; group 2, 18 normal children; and group 3, 12 boys with constitutional delay in growth and puberty who were in early puberty. Children in groups 1 and 2 each had a 24 hour serum growth hormone profile (sampling every 20 minutes) and concurrent urine collection. The 12 boys in group 3 had a total of 21 profiles (sampling every 15 minutes for 12 hours) and concurrent urine collections. In the prepubertal children (n = 17), in both groups 1 and 2, there was a significant correlation between mean serum growth hormone and total uGHng/g creatinine. There were also significant correlations between total uGHng/g creatinine and both peak serum growth hormone and mean amplitude of the pulses in the growth hormone profile. In the pubertal children (n = 22), in groups 1 and 2, whether combined or in separate groups, there was no significant correlation between total uGHng/g creatinine and mean serum growth hormone, peak serum growth hormone, or mean amplitude of the pulses in the growth hormone profile. In group 3 there were significant correlations between total uGHng/g creatinine and both the mean serum growth hormone and mean amplitude of the pulses in the profile. Therefore uGH estimations appear to correlate well with serum growth hormone profiles in children who are prepubertal or in early puberty, but not in those further advanced in pubertal development. These results may reflect a variation in the renal handling of growth hormone during pubertal development. uGH estimation may be an unreliable screening investigation for growth hormone sufficiency in mid to late puberty.

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.

Increase in urinary growth hormone excretion in puberty

During the pubertal years the overnight urinary excretion rate of growth hormone (hGHu) increases to three to four times the prepubertal rate, reaching a peak in girls at 13 years and in boys at 15 years. After puberty the mean rate of overnight hGHu is twice that before puberty.