Re-interpreting the Appropriate Growth Hormone Response to Hypoglycaemia

Background: The “Newcastle work-up” is laboratory investigation to elucidate metabolic or endocrine causes of hypoglycaemia. One of the tests it measures is growth hormone GH,which should increase during hypoglycaemia. In our recent clinical experience, GH levels have been sub-optimal during hypoglycaemia. The cut off value for growth hormone levels is 7mcg/L,reading below is deemed suboptimal and warrant clinician to investigate further.

Aims/Objectives :To identify if the pre-set cut-off value for GH during hypoglycaemia during Newcastle work-up is appropriate and likely or not to identify GH deficiency. The study population was all paediatric patients attending the Paediatrics Department UHL with GH levels over 12 months from January to December 2018, inclusive.

Methods: Retrospective review from a prospectively collected database of glucose and GH,including growth velocity, centiles, mid-parental height ranges and IGF-1 during hypoglycaemia in the Newcastle work-up. GH levels were subdivided into five subgroups: <1; 1-2.9; 3-4.9; 5-6.9; >7 mcg/L.

Results:Forty Newcastle work-ups were performed on N=40 patients during the study period;GH results according to 5 subgroups are shown in Figure 1. N=3/39 (8%) GH levels were >7 mcg/L, which is the pre-defined normal range result. The mean GH was 3.83 and median GH 3.19 mcg/L.IGF-1 level was available on 12/40; 11/40 were normal. N=1/40 IGF-1 was low and this patient had decelerating height centile, GHST was subsequently normal.N=19/40 patients had normal growth velocity and growth centiles,Data on remaining patients are incomplete or pending.GHST was performed on 3/40 children.All had normal GHST results.

Conclusion: These data are limited and some results are pending. But no patient has documented GH deficiency or loss of height centiles, despite only N=3/40 having adequate GH during hypoglycaemia during Newcastle testing.

Recommendations: These data suggest that the optimal level for GH during testing for causes of hypoglycaemia should be re-evaluated in further and larger prospective studies