The Diagnosis of Growth Hormone Deficiency in Adults1

Marianne Andersen, Jørgen Hangaard and Claus Hagen

Odense University Hospital Odense C, Denmark DK-5000

Gianluca Aimaretti and Ezio Ghigo

University of Turin 10126 Turin, Italy

We were most interested to read the recommendation for using the insulin tolerance test (ITT) for diagnosing growth hormone deficiency (GHD) (1), and we would like to comment on the choice of this test and of the recommended GH cut-off limit of 3 µg/L. The evaluation or introduction of a GH-stimulation test requires the definition of a reference interval for healthy adults, taking into consideration the possible influences of sex, age, obesity, and substitution therapy. The current choice of method for diagnosing GHD in adults is clearly arbitrary. In earlier studies of the clinical effect of GH therapy on patients suffering from GHD, very low stimulated GH-levels were used as inclusion criteria (2, 3, 4, 5, 6). In addition, it was, at that time, impossible to base the cut-off limits for GH on scientific data, as no reference interval had been published for stimulated GH-responses to GH-stimulation tests. It has been suggested recently that the criterion for the diagnosis of GHD in adults should be a peak GH-response to the ITT of less than 3 µg/L (1). This limit was based on the further reduction of reported cut-off limit of 5 µg/L in normal subjects (7) to "allow for the influences of age and adiposity" (1). Hoffmann et al. (7) chose age, sex, and body mass index (BMI)-matched controls, as these parameters have been considered to be important to the peak GH-responses to the ITT. However, the matching of control subjects does not imply that these results can be automatically extrapolated to healthy adults, as the controls included obese and elderly individuals. It should be noted that the mean BMI for this group of individuals was 25.1 kg/m2 (min-max: 15.6–38.9), and that obesity in otherwise healthy adults has been associated with markedly impaired GH-responses to the ITT (8, 9). Furthermore, although the mean age of this group was 47.3 yr (min-max: 17–78), the peak GH-responses of the most elderly subjects to the ITT were not significantly lower than those of the rest of the group (7). The use of the lowest peak GH-response obtained from a control group that includes aged and obese subjects risks reducing the sensitivity of the ITT in normal-weight patients with suspected GHD.

The marked discrepancies among GH-assays did not become apparent until after monoclonal assays came into widespread use. This is not surprising, as different monoclonal antibodies would be expected to recognize different GH forms in a disparate manner (10), and problems caused by incorrect calibration and the use of inappropriate mass units have been recorded (11). Nevertheless, the relationship between the two assays that have been studied (i.e. the polyclonal Pharmacia assay and the monoclonal Dissociation-Enhanced Lanthanide Fluoro-Immuno-Assay (DELFIA) assay) is reasonably constant, and it is, in fact, possible to use a conversion factor to compare the results of the two assays. The conversion factor for converting RIA (Pharmacia AB, Uppsala, Sweden) to DELFIA (Wallac, Turku, Finland) is: DELFIA = RIA x 0.63. The conversion factor proved to be constant throughout the concentration range, and the distribution around the mean accorded with the analytical imprecision of the two methods (Andersen et al. to be published).

Although more than 15 different GH-stimulation tests are available, opinion is divided concerning which test is to be used for specific patient groups. Moreover, many of the tests are unreliable.

The effect of the combination of pyridostigmine (PD) and growth hormone-releasing hormone (GHRH) on peak GH-levels has been studied by teams including Ghigo et al. (12), Arvat et al. (13), and Andersen et al. (14). The effect produced is based on direct GHRH stimulation of the pituitary gland and PD-inhibition of somastostatin (15, 16, 17, 18, 19). 120 mg PD is administered orally 60 min before the injection of GHRH (1 µg/kg, time 0) as an iv bolus. Serum samples for the measurement of GH-levels are then taken at 0, 20, 30, 45, 60, and 90 min. The reference interval for the peak GH responses to the PD-GHRH test was established in 40 healthy adults (14), all of whom were 22–58 yr of age and within 10% of ideal body weight. The GH responses were Log-Gaussian distributed and were unaffected by factors such as age, sex, and the use of oral contraceptives. The 95% reference interval was 42–422 mU/L. Please note that the RIA (Pharmacia AB, Uppsala, Sweden) was used in this study. The 2.5 percentile (-1.96 SD) of 42 mU/L was used as the cut-off limit for the biological GH responses to the PD-GHRH test for adults aged 22–58 yr, and the 90% Cl for this percentile ranged from 31–56 mU/L. Using the established cut-off limit of 42 mU/L for the PD-GHRH test (14), and the conventional cut-off limit of 20 mU/L for the ITT (20), a high level of agreement between the two tests, 44/47 (94%), was found (14). This is a particularly convincing result, especially considering the characteristics of the patients examined. In contrast to the results of the study carried out by Andersen et al. (14), most studies using GH stimulation tests included only patients who were considered GH-deficient (7, 12). The ITT may not be the best tool for the diagnosis of GHD in adults. Hoeck et al. (21) have questioned the reproducibility of the ITT in normal adults. A reference interval for the ITT will be difficult to establish, and it may prove impossible to evaluate the possible influences of sex, age, body composition, and cortisol levels on ITT-stimulated GH levels, as patients find the ITT unpleasant. Furthermore, the ITT is potentially hazardous (22). In contrast to this, no severe side effects and only minor, transitory complaints were recorded in over 400 PD-GHRH tests carried out in Milan and Odense. Of those tested, approximately 10% suffered gastrointestinal discomfort, with 1/10 of these experiencing diarrhea and nausea, and the remainder experiencing heartburn and meteorism. Approximately 10% of those tested displayed tics, and the injection of GHRH caused flushing lasting 30 seconds in approximately 50% of the subjects. Obesity in otherwise healthy adults has been associated with markedly impaired GH-responses to the ITT (8, 9), to the PD-GHRH test (23, 24, 25, 26), and to the arginine-GHRH test (27). However, to establish reference intervals for this group of patients it is essential to study the impact of over-weight on peak GH-responses.

Elderly subjects also pose new diagnostic problems. Ghigo et al. found the PD-GHRH test to be a very reliable tool for the biological measurement of GHD in 20–40-yr-olds (12), but normal adults aged 40–65 yr were not included in this study. Some subjects from the 65+ age group who were considered normal still displayed low GH-responses to the PD-GHRH test (12). The combination of arginine and GHRH produced high GH-responses in the 65+ age group, and even in 80-yr-olds. Because of its effectiveness in even very elderly subjects, Ghigo et al. preferred the combination of arginine and GHRH for elderly patients with suspected GHD (12). It must be remembered that basal GH and insulin-like growth factor (IGF)-I levels are reduced in normal, elderly individuals (28, 29), and that GH-levels in some normal individuals will almost certainly be low at a relatively young age. Early somatopause thus makes the diagnosis of GHD in patients over the age of 65 a discussion of the general attitude toward "the diagnosis GHD" in healthy old people. This is an area which merits thorough investigation.

Among the many tests available for the diagnosis of GHD in adults, a particularly strong case can be made for choosing the PD-GHRH test, as it is easy to perform, safe, potent, reproducible, and reliable (14). Furthermore, the cut-off limit of 42 mU/L (90% Cl 31–56 mU/L) has already been established for this test (14). The arginine-GHRH test might also be considered as a diagnostic test (12).

GHD-evaluation should be a part of the total evaluation procedure for patients with suspected hypothalamic and/or pituitary diseases.

In conclusion: 1) Important information can be gathered from the clinical characteristics of the patients. Insufficiency of ACTH will imply diminished peak GH-responses to the ITT in approximately 91% (30) to 100% (14) of patients. However, it should be noted that Toogood et al. (30) reported that 28% of patients suffered from only GHD and not from insufficiency of any other pituitary hormones. Therefore, GHD does not necessarily imply deficiency of other pituitary hormones; 2) A subnormal total IGF-I value essentially confirms the diagnosis, whereas IGF-l levels within the normal range do not preclude GHD (7, 14); 3) We recommend using the PD-GHRH test to diagnose GHD and would like to stress that in normal subjects aged 22–58 yr, the PD-GHRH-stimulated GH-responses were not significantly affected by factors such as age, sex, or the use of oral contraceptives (14).

However, the influence of body composition still remains to be evaluated, and it is still necessary to clarify the state of somatotrophs in healthy elderly people.

Footnotes

1 Received May 1, 1997. Address correspondence to: Marianne Andersen, Department of Endocrinology, Odense University Hospital, Odense C, Denmark DK-5000. Back

References

  1. Thorner MO, Bengtsson BA, Ho KY, et al. 1995 The diagnosis of growth hormone deficiency (GHD) in adults (letter). J Clin Endocrinol Metab. 80:3097–3098.[Medline]
  2. Jørgensen JOL, Thuesen L, Ingemann-Hansen T, et al. 1989 Beneficial effects of growth hormone treatment in GH-deficient adults. Lancet. 3:1221–1225.
  3. Salomon F, Cuneo RC, Hesp R, Sönksen PH. 1989 The effects of treatment with recombinant human growth hormone on body composition and metabolism in adults with growth hormone deficiency. N Engl J Med. 321:1797–1803.[Abstract]
  4. Mårdh G, Lundin K, Borg G, Jonsson B, Lindeberg A. 1994 Growth hormone replacement therapy in adult hypopituitary patients with growth hormone deficiency: Combined data from 12 European placebo-controlled clinical trials. Endocrinol Metab. 1 [Suppl A]:43–49.
  5. Whitehead HM, Boreham C, McIlrath EM, et al. 1992 Growth hormone treatment of adults with growth hormone deficiency: results of a 13-month placebo controlled cross-over study. Clin Endocrinol (Oxf). 36:45–52.[Medline]
  6. Whitehead HM, Aiken B, Lewis S, Sheridan B, Hadden DR. 1991 Physiological growth hormone secretion in adult growth hormone deficiency: comparison with normal controls. Clin Endocrinol (Oxf). 34:371–376.[Medline]
  7. Hoffman DM, O’Sullivan AJ, Baxter RC, Ho KK. 1994 Diagnosis of growth-hormone deficiency in adults. Lancet. 343:1064–1068.[Medline]
  8. Rasmussen MH, Hvidberg A, Juul A. 1995 Massive weight loss restores 24-hour growth hormone release profiles and serum insulin-like growth factor-l levels in obese subjects. J Clin Endocrinol Metab. 80:1407–1415.[Abstract]
  9. Cordido F, Dieguez C, Casanueva FF. 1990 Effect of central cholinergic neurotransmission enhancement by pyridostigmine on the growth hormone secretion elicited by clonidine, arginine, or hypoglycemia in normal and obese subjects. J Clin Endocrinol Metab. 70:1361–1370.[Abstract]
  10. Baumann G. 1990 Growth hormone binding proteins and various forms of growth hormone: implications for measurements. Acta Paediatr Scand Suppl. 370:72–80.[Medline]
  11. Seth J, Ellis AR, Sturgeon CM. 1995 UKNEQUAS for peptide hormones and related substances. 19–22 (Abstract).
  12. Ghigo E, Aimaretti G, Gianotti L, Bellone J, Arvat E, Camanni F. 1996 New approach to the diagnosis of growth hormone deficiency in adults. Eur J Endocrinol. 134:352–356.[Medline]
  13. Arvat E, Cappa M, Casanueva FF. 1993 Pyridostigmine potentiates growth hormone (GH)-releasing hormone-induced GH release in both men and women. J Clin Endocrinol Metab. 76:374–377.[Abstract]
  14. Andersen M, Hansen TB, Støving RK. 1996 The pyridostigmine-growth-hormone-releasing-hormone test in adults. The reference interval and a comparison with the insulin tolerance test. Endocrino Metab. 3:197–206.
  15. Richardson SB, Hollander CS, D’Eletto RD, Greenleaf PW, Than C. 1980 Acetylcholine inhibits the release of somatostatin from rat hypothalamus in vitro. 107:1837.
  16. Locatelli V, Torsello A, Redaelli M, Ghigo E, Massara F, Müller EE. 1986 Cholinergic agonist and antagonist drugs modulate the growth hormone response to growth hormone-releasing hormone in the rat: evidence for mediation by somatostatin. J Endocrinol. 111:271–278.[Abstract]
  17. Torsello A, Panzeri G, Cermenati P, et al. 1988 Involvement of the somatostatin and cholinergic systems in the mechanism of growth hormone autofeedback regulation in the rat. J Endocrinol. 117:273–281.[Abstract]
  18. Wehrenberg WB, Wiviott SD, Voltz DM, Giustina A. 1992 Pyridostigmine-mediated growth hormone release: evidence for somatostatin involvement. Endocrinology. 130:1445–1450.[Abstract]
  19. Casanueva FF, Villanueva L, Dieguez C, et al. 1986 Atropine blockade of growth hormone (GH)-releasing hormone-induced GH secretion in man is not exerted at pituitary level. J Clin Endocrinol Metab. 62:186–191.[Abstract]
  20. Wass JAH, Besser GM. 1989 Tests of pituitary function. In: DeGroot LJ, ed. Endocrinology Philadelphia: W.B. Saunders; 492–502.
  21. Hoeck HC, Vestergaard P, Jakobsen PE, Laurberg P. 1995 Test of growth hormone secretion in adults: poor reproducibility of the insulin tolerance test. Eur J Endocrinol. 133:305–312.[Medline]
  22. Shah A, Stanhope R, Matthew D. 1992 Hazards of pharmacological tests of growth hormone secretion in childhood. Brit Med J. 304:173–174.[Medline]
  23. De Marinis L, Mancini A, Zuppi P, et al. 1992 Influence of pyridostigmine on growth hormone (GH) response to GH-releasing hormone pre- and postprandially in normal and obese subjects. J Clin Endocrinol Metab. 74:1253–1257.[Abstract]
  24. Cordido F, Casanueva FF, Dieguez C. 1989 Cholinergic receptor activation by pyridostigmine restores growth hormone (GH) responsiveness to GH-releasing hormone administration in obese subjects: evidence for hypothalamic somatostatinergic participation in the blunted GH release of obesity. J Clin Endocrinol Metab. 68:290–293.[Abstract]
  25. Ghigo E, Mazza E, Corrias A. 1989 Effect of cholinergic enhancement by pyridostigmine on growth hormone secretion in obese adults and children. Metabolism. 38:631–633.[Medline]
  26. Castro RC, Vieira JG, Chacra AR, Besser GM, Grossman AB, Lengyel AM. 1990 Pyridostigmine enhances, but does not normalise, the GH response to GH-releasing hormone in obese subjects. Acta Endocrinol (Copenh). 122:385–390.[Medline]
  27. Maccario M, Valetto MR, Savio P, et al. 1997 Maximal secretory capacity of somatotrope cells in obesity: comparison with GH deficiency. Int J Obesity. 21:27–32.[CrossRef]
  28. Iranmanesh A, Lizarraide G, Veldhuis JD. 1991 Age and relative adiposity are specific negative determinants of the frequency and amplitude of growth hormone (GH) secretory bursts and the half-life of endogenous GH in healthy men. J Clin Endocrinol Metab. 73:1081–1088.[Abstract]
  29. Ghigo E, Goffi S, Nicolosi M, et al. 1990 Growth hormone (GH) responsiveness to combined administration of arginine and GH-releasing hormone does not vary with age in man. J Clin Endocrinol Metab. 71:1481–1485.[Abstract]
  30. Toogood AA, Beardwell CG, Shalet SM. 1994 The severity of growth hormone deficiency in adults with pituitary disease is related to the degree of hypopituitarism. Clin Endocrinol (Oxf). 41:511–516.[Medline]