Insulin test

Purpose

To investigate somatotropic function.
To investigate the hypothalamo-pituitary-adrenal system.

Subject preparation

Fasting for 12 hrs and at rest for 30 min (although babies of under one year and hypoglycaemic subjects should be given 200 ml of milk at 5 a.m.).

Product

• Regular insulin.

Dose

• Insulin: 0.1 U/kg body weight.
  In babies of under 12 months, the elderly and subjects at risk of panhypopituitarism or hypoglycaemia, the dose should be cut in half, i.e. 0.05 U/kg body weight.

Protocol

Commence the perfusion of normal saline 30 minutes before the challenge.

• Samples (dry and fluoride tubes) at T-15 and T0.
• IV injection of the correct dose of insulin.
• Samples (dry and fluoride tubes) at time intervals: T+15, T+30, T+45, T+60, T+90 and T+120 min.

Samples

After centrifugation of the samples, freeze the serum at –20°C and store the plasma at +4°C.

Side effects

Close medical supervision because of the risk of HYPOGLYCAEMIA associated with fasting coupled with the insulin: have ready a syringe containing 20 ml 20% glucose solution and a 1 mg vial glucagon.

Contraindications

• This test is contraindicated in the newly-born and infants.

Assays

• GH.
• Cortisol.