Growth Hormone Suppression Test (Post-Glucose Administration)

Abstract

Indication

To establish the diagnosis of acromegaly when there is modest elevation of IGF-1 (< 2-fold upper limit of normal) with absent or equivocal clinical features [1].

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FormalPara Indication:

To establish the diagnosis of acromegaly when there is modest elevation of IGF-1 (< 2-fold upper limit of normal) with absent or equivocal clinical features [1]

FormalPara Preparation:

10 h fasting

FormalPara Materials Needed:

Glucose drink 75 g

FormalPara Assay for GH:

Immunoenzymatic assay

FormalPara Precautions:

Patients may complain of nausea.

FormalPara 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].

FormalPara 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].

FormalPara 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).

• 5. Draw glucose and growth hormone levels at 30, 60, 90, and 120 min [7].

• 6. (Include insulin levels at baseline, 30, 60, 90, and 120 min only if requested).

Patient label: ▁

Physician name and signature: ▁

RN performing the procedure: ▁

Additional orders by physician: ▁

GH suppression test	Baseline	30 min	60 min	90 min	120 min
Glucose
GH