Endocrine Abstracts

Introduction: We previously used an assay measuring GH levels in microgram per litre. Peak GH levels >20, 10–20 and <10 μ/l representing sufficiency, partial deficiency and deficiency of GH respectively. With a new assay introduced in 2008 peak GH levels >8, 4–8 and <4 μg/l were quoted as normal, partial deficiency and deficiency. Although the patient groups tested were different we would have expected to have approximately similar rates of ‘abnormal’ results. However, it appeared that proportion of abnormal results was higher.

Aim: To determine if the proportion of results considered abnormal changed following the introduction of the new assay.

Methods: Peak stimulated GH levels measured in microgram per liter, between March 2004–September 2008 were compared those in microgram per liter from October 2008–April 2011. Each test was considered as a separate event. χ² test was used to compare the proportions in each category.

Results: 46 GH stimulation tests (average 10/years) were carried out in first period, 69 tests (average 26/years) were carried in the second. Normal (>20 μ/l) 45.6%, partial (10–20 μ/l) 30.5% and deficiency GH (<10 μ/l) 23.9%. Normal (>8 μ/l) in 34.7%, partial (4–8 μ/l) 37.6% and deficiency GH (<4 μ/l) 23.1% (no result 4.6%). Although there was a trend towards more abnormal results this was non significant, P=0.55. However, had we used cut offs advised by other centres with the new assay (<7 μ/l as deficiency) the proportions of tests would have been 42% normal, 30.4% partial and 23% GH deficiency, i.e. very similar to earlier.

Conclusion: The new assay has highlighted a trend to a higher proportion of tests with abnormal GH on stimulation testing. By changing our diagnostic criteria to that used by other centres this is eliminated.