If your GP has just handed you a blood test form, you've probably already typed "how long does glucose test take" into Google, hoping to work out how much of your day to set aside.

The short answer is around 10 minutes for the blood draw itself. But an OGTT needs you to stay at the hospital for just over two hours, and results usually take anywhere from a few days to a few weeks.

"How long does the glucose test take" really depends on which test you mean. This article walks through each type in turn.

If you're thinking about continuous monitoring to sit alongside periodic blood tests, a SIBIONICS continuous glucose monitor offers up to 14 days of trend data per sensor.

⚠️ This article is for information only and is not medical advice. Follow the guidance you receive from your GP or hospital for your specific test.

The Quick Answer — Test Duration At A Glance

Many readers also ask "how long does the glucose test take" in a slightly different way — the answer depends on the test. The table below summarises the five most common options.

Test type	Time at clinic	Fasting needed	Common use	Result turnaround
Fasting plasma glucose (FPG)	About 10 minutes for the draw	Yes, 8–10 hours	Diabetes screening, annual check	A few days to a few weeks
Random blood glucose	About 10 minutes for the draw	No	Acute symptom assessment	A few days to a few weeks
HbA1c	About 10 minutes for the draw	No	Long-term glucose control review	A few days
OGTT (oral glucose tolerance test)	Just over 2 hours	Yes, 8–10 hours	Gestational diabetes screening, diagnosis	Same day at some hospitals, a few days at others
CGM (continuous glucose monitor)	Worn at home	No	Day-to-day trend monitoring	Displayed in real time

Each test is broken down in the sections that follow.

How Long Does A Fasting Or Random Blood Glucose Test Take?

For most GP appointments, "how long does a glucose test take" really means how long the blood draw takes. The NHS blood test page is direct on this point: "The test usually takes about 10 minutes" [1] — that is the time at the actual blood draw.

A fasting plasma glucose (FPG) test asks you not to eat for 8–10 hours beforehand, so it is typically booked first thing in the morning.

A random blood glucose test has no fasting requirement and can be done at any time of day. The blood draw itself takes much the same time for both.

The draw itself involves a small needle into a vein at the inner elbow for a few seconds, then a cotton-wool pad pressed against the site for about a minute. Waiting and check-in time at the clinic vary, but 30–60 minutes is fairly typical.

How Long Does The HbA1c Test Take?

HbA1c works differently from a one-off glucose reading. Diabetes UK explains it like this: "HbA1c is your average blood glucose (sugar) levels for the last two to three months" [2]. It reflects the average over a 2–3 month window.

In practical terms, "glucose test how long does it take" is at its simplest for HbA1c — a single tube of blood, around 10 minutes at the clinic, no fasting needed.

HbA1c is one of the preferred tests for diagnosing type 2 diabetes in the UK and is the core measure for tracking long-term glucose control once you've been diagnosed. Repeat HbA1c every 3–6 months is common.

How Long Does A Glucose Tolerance Test Take?

In UK search results, "how long does a glucose tolerance test take" most often refers to the pregnancy OGTT.

The NHS gestational diabetes page states: "The screening test is called an oral glucose tolerance test (OGTT), which takes about 2 hours" [3].

The Diabetes UK page dedicated to gestational diabetes testing puts it slightly more precisely: "The OGTT takes just over two hours to complete" [4]. Both sources line up on "how long does the glucose tolerance test take".

The procedure looks like this. A first blood sample is taken in the morning on an empty stomach. You then drink a 75 g glucose drink, sit quietly for two hours, and have a second blood sample.

The NHS also notes that you should "fast for 8 to 10 hours", and you can drink water (same source as [3]).

A pregnancy OGTT is usually arranged between 24 and 28 weeks of pregnancy (same source as [3]). Outside of pregnancy, an OGTT used for diabetes diagnosis follows a similar protocol, although HbA1c is more often used in routine UK practice.

If you want a longer view alongside the OGTT, the continuous monitoring systems offered by various cgm suppliers can help. That leads naturally to the next question — "how long does a glucose test take to get results".

How Long Does It Take To Get Glucose Test Results?

"How long does it take to get glucose test results" and "how long does a glucose test results take" are two phrasings of the same question.

The NHS page on diagnosing type 2 diabetes gives the most direct answer: "The results usually take a few days" [5].

The NHS general blood test page adds that you may get your results "after a few days, and usually within a few weeks" (same source as [1]). The exact timing depends on the laboratory schedule and how quickly results are passed back to your GP.

The Diabetes UK HbA1c page is more concise: "You should get the results quickly" (same source as [2]) — most commonly within 1–3 working days.

A pregnancy OGTT is the exception. Diabetes UK warns that "You won't always receive the tests results on the same day as the test" (same source as [4]). Some larger pregnancy units share results the same day, others take a few days.

⚠️ Abnormal results are usually flagged proactively by the lab or your GP. If results take longer than the usual turnaround and you haven't heard back, you can check via the NHS App or ring your GP.

If you'd like to track day-to-day trends to reduce reliance on one-off tests, the continuous monitoring options sold by different cgm supplies retailers may be worth considering.

So "How quickly do I get glucose test results?" — pulling the strands together: HbA1c is typically 1–3 days, FPG or random can be a few days to a few weeks, and OGTT can range from same day to a few days.

Why Do Different Tests Take Different Times?

People often ask "glucose test how long does it take" without realising the tests are biologically different.

HbA1c measures glycated haemoglobin. Red blood cells live for around 120 days, so a single sample reflects average blood glucose over the last 2–3 months. No fasting, no repeat draw.

FPG and random tests are "snapshot" measurements — they only capture plasma glucose at the moment of the draw. FPG requires an 8–10 hour fast to rule out the influence of recent food.

The OGTT is a "dynamic" test. You drink 75 g of glucose and your body's response is observed for two hours. Because the response curve is the point, the total time stretches beyond two hours.

A CGM is "continuous". It reads an estimated glucose value from interstitial fluid every few minutes, building up a multi-day trend.

How Does A CGM Fit Into This Picture?

One thing to clarify first — a CGM measures glucose in the interstitial fluid, not directly in the blood.

Hanson et al (2024) describe CGM systems as "continuously measuring glucose in the interstitial fluid in persons ≥ 2 years of age" [6].

The same paper notes that "interstitial glucose levels may fail to keep pace with rapidly rising or falling BG levels, often referred to as sensor lag". That means CGM readings sit a few minutes behind a simultaneous fingerstick value.

A CGM is not a replacement for an OGTT or HbA1c — diabetes diagnosis still relies on the laboratory tests above.

However, the multi-day trends a CGM produces can help clinicians review overall glucose control and spot overnight or post-meal patterns.

Take the SIBIONICS GS3 CGM as an example. Its official user guide states the sensor can be worn for up to 14 days per session, with factory calibration that needs no fingerstick blood.

Specifications such as wear site, wear days, water resistance and app compatibility vary considerably between CGM brands, so refer to each brand's accompanying user guide.

Note: SIBIONICS CGM is a CE-certified medical device sold in the European market. It has not received FDA approval and is not sold in the US market.

Verdict

Back to the headline question — "how long does glucose test take". The answer has three layers:

First, the blood draw itself is around 10 minutes (same source as [1]). That covers FPG, random and HbA1c.

Second, an OGTT keeps you at the clinic for just over two hours (same sources as [3] and [4]). Third, results usually come back within a few days to a few weeks (same source as [5]).

If you want day-to-day trends rather than a one-off lab number, a CGM is a useful adjunct but not a diagnostic replacement. You can compare the features offered by different cgm brands on the market.

This article is for information only and is not medical advice. Follow your GP or hospital's instructions for your specific test.

FAQ

Q: Can I get my pregnancy OGTT results the same day?

A: Not always. Diabetes UK warns that same-day results are not guaranteed (see [4]). Some hospitals share results on the day. Others ask you to wait a few days.

Q: Can I drink water on test day?

A: Yes. The NHS gestational diabetes page allows water (see [3]). However, juice, coffee, tea with milk and similar drinks break the fast and should be avoided.

Q: Can I use a CGM instead of an OGTT?

A: No. A CGM is a monitoring aid. Diabetes diagnosis still relies on a laboratory OGTT, HbA1c or FPG.

Q: Which is more accurate — HbA1c or OGTT?

A: They measure different things. HbA1c reflects a long-term average. An OGTT reflects acute glucose tolerance. Clinicians choose by context, and sometimes use them together.

Q: My results have not arrived after five days — what now?

A: Check the NHS App or ring your GP surgery. Abnormal results are usually flagged proactively.

Q: Are private results faster than NHS results?

A: Some private providers offer a faster turnaround (24–72 hours), but the cost varies widely. Check first that the test you are paying for is recognised by the relevant UK clinical guidance.

References

[1] NHS. Blood tests. nhs.uk. https://www.nhs.uk/tests-and-treatments/blood-tests/
[2] Diabetes UK. HbA1c. diabetes.org.uk. https://www.diabetes.org.uk/about-diabetes/looking-after-diabetes/hba1c
[3] NHS. Gestational diabetes. nhs.uk. https://www.nhs.uk/conditions/gestational-diabetes/
[4] Diabetes UK. Gestational diabetes tests. diabetes.org.uk. https://www.diabetes.org.uk/about-diabetes/gestational-diabetes/test
[5] NHS. Type 2 diabetes – Getting diagnosed. nhs.uk. https://www.nhs.uk/conditions/type-2-diabetes/getting-diagnosed/
[6] Hanson K, et al. (2024). Comparison of Point Accuracy Between Two Widely Used Continuous Glucose Monitoring Systems. J Diabetes Sci Technol. https://pmc.ncbi.nlm.nih.gov/articles/PMC11089878/

Disclaimer

This article is for educational purposes only and does not replace professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition.

Author Information

This article was written by the SIBIONICS Professional Health Content Team. The author has years of research experience in CGM and diabetes management, helping users optimise their device experience through science-based practices.

Last Updated: May 19, 2026

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