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Blood test

Growth hormone stimulation test

Growth hormone stimulation test: what it measures, why a doctor orders it, how to prepare, and what a high or low result can mean - with private and NHS access routes in the UK.

Key facts

At a glance

  • What it measures: how much growth hormone your pituitary can produce when deliberately provoked - single random levels are meaningless because the hormone is released in pulses.

  • Why it is ordered: in children with concerning growth failure and adults with suspected growth hormone deficiency after pituitary disease or treatment.

  • This is a supervised half-day in a clinical unit - fasted, with a cannula, a provoking agent such as glucagon or arginine, and timed samples over two or more hours.

  • Reference ranges: the peak response to the stimulus is what counts, judged against assay- and protocol-specific thresholds. Every laboratory publishes its own interval, so the range printed on your report is the one that applies to you.

  • A raised result or adequate peak excludes significant growth hormone deficiency. A low result or blunted peak supports deficiency and opens the discussion about growth hormone replacement.

  • Results typically take a few days to two weeks, because the sample is analysed in batches at a specialist laboratory.

The full picture

What this test tells you, and how to get it

The growth hormone stimulation test measures how much growth hormone your pituitary can produce when deliberately provoked - single random levels are meaningless because the hormone is released in pulses. Doctors most often request it in children with concerning growth failure and adults with suspected growth hormone deficiency after pituitary disease or treatment. This is a supervised half-day in a clinical unit - fasted, with a cannula, a provoking agent such as glucagon or arginine, and timed samples over two or more hours. The peak response to the stimulus is what counts, judged against assay- and protocol-specific thresholds, and reference intervals genuinely differ between laboratories, so no single number should be treated as a universal cut-off - your result is always read against the range printed on your own report. Broadly, a raised result or adequate peak excludes significant growth hormone deficiency, while a low result or blunted peak supports deficiency and opens the discussion about growth hormone replacement, and either finding is interpreted alongside your symptoms, medication and other results rather than in isolation. Results typically take a few days to two weeks, because the sample is analysed in batches at a specialist laboratory.

In the UK there are two routes to this test. Your NHS GP can arrange it free of charge when it is clinically indicated, though getting the appointment, the blood draw and the follow-up discussion can add days to weeks depending on local demand. Privately, the growth hormone stimulation test can usually be booked within days - through a private GP, a walk-in phlebotomy clinic or a self-request home-testing service - exclusively through endocrine units - this is not a test any phlebotomy service can offer. A private result still deserves a clinician's interpretation: an isolated number without context is where most confusion about blood tests begins.

A quiet reminder

This guide is for information, not medical advice.

Your own clinician knows your history and can tell you which parts apply to you. Reference ranges vary between laboratories - always read your result against the interval printed on your own report. Next review of this page: 2027-09-27.

Frequently asked

Common questions about Growth hormone stimulation test.

Quick, plain-English answers to what people ask us most.

  • What is a growth hormone stimulation test?

    This is a specialist blood test that checks how well your pituitary gland produces growth hormone in response to a stimulating medication. It's used to help diagnose growth hormone deficiency in both children and adults.

  • Why would a doctor order this test?

    It's typically requested when growth hormone deficiency is suspected, for example due to slow growth in children, pituitary disease, or symptoms such as low energy and reduced muscle mass in adults with a known pituitary condition. It's usually arranged by an endocrinologist rather than as a routine screen.

  • Do I need to prepare for this test?

    You'll usually need to fast beforehand, and the test is performed under medical supervision, often over several hours. Your specialist team will give you specific instructions, including any medications to pause.

  • What happens during the test?

    A stimulating agent is given, often by injection, and blood samples are taken at set intervals afterwards to measure how your growth hormone levels rise. It's done in a clinical setting because you'll be monitored throughout.

  • Does it hurt or carry any risks?

    You'll have a cannula placed for repeated blood sampling, which involves a brief needle prick, and mild side effects such as flushing, nausea or dizziness from the stimulating agent are possible. Medical staff monitor you throughout to manage any reaction.

  • How long do results take?

    Because this involves multiple samples and specialist analysis, results typically take longer than a routine blood test, often around one to two weeks. Your endocrinologist will discuss the results with you at a follow-up appointment.

  • What do abnormal results mean, and what happens next?

    A blunted growth hormone response can support a diagnosis of growth hormone deficiency, which may need further pituitary imaging and hormone assessment. Your specialist will interpret the result alongside your symptoms and other tests before discussing treatment options.

  • How much does it cost privately, and is it available on the NHS?

    This test is available on the NHS but usually requires referral to an endocrinology service and can involve a wait for a hospital appointment. Private endocrinology assessment can often be arranged more quickly, with results reviewed by a specialist; cost varies by provider.

  • Is the test accurate and reliable?

    It's considered the recognised way of assessing growth hormone reserve, though results need careful interpretation alongside clinical findings and sometimes a second stimulation test. Timing, technique and the stimulating agent used can all affect results, which is why it's performed in specialist centres.

  • How do I book this test privately, and how quickly can I be seen?

    This test requires an endocrinologist to organise and supervise it, so booking usually starts with a private specialist consultation.