Assay for GH:
Immunoenzymatic assay
Precautions:
Patients may complain of nausea.
Interpretation:
Diagnosis of acromegaly: Using ultrasensitive assays, a GH suppression to < 0.4 ng/ml is considered the gold standard test to rule out acromegaly [2]. The GH cutoff value may vary based on the assay used. The authors use a GH cutoff value < 0.2 ng/mL as a normal response, using a immunoenzymatic assay at Cleveland Clinic [1].
A GH level < 1 ng/mL early after surgery, in the absence of presurgical usage of somatostatin analogs, predict long-term remission [3].
Caveats:
Endocrinologists should be familiar with the assays used in their laboratories, including the expected normal nadir GH level after oral glucose e [4].
Elevated IGF-1 levels more than twice the upper limit of normal in patients with clinical features suggestive of an underlying acromegaly, are usually sufficient to establish the diagnosis [1].
Failure of adequate suppression or a paradoxical rise in GH level can be seen in starvation, anorexia nervosa, and chronic renal failure, but these conditions are typically associated with low IGF-1 levels.
GH levels during OGTT have not been well studied in patients with diabetes mellitus, and in those on estrogen . In the authors’ experience, patients with diabetes who are not poorly controlled achieve GH levels during OGTT similar to those without DM [5].
A paradoxical GH secretary response to glucose may be seen in premature infants, children of tall stature, and adolescents [6].
Procedure:
Completed as outpatient.
1.
Establish saline lock.
2.
Check POC BG.
3.
Draw baseline growth hormone.
4.
Give glucose 75 g orally (glucose drink).
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