Test it in Chiswick: our Omnia Essential blood test costs £89, with your result explained in person by a practitioner. No GP referral needed. Book this test or call 020 4515 0000. Or compare every blood test and price, from £39.
What is a fasting blood test?
A fasting blood test is taken after you have had nothing to eat or drink except water for a set time, usually 8 to 12 hours. It is used when food would change the result, most often for fasting glucose, which shows how your body handles sugar, and a fasting lipid profile, which measures cholesterol and triglycerides. Whoever orders the test will tell you if you need to fast. Our guides to cholesterol levels and HbA1c levels explain what the results mean.
Which blood tests need fasting?
Fasting matters when eating would change the result. Blood glucose rises after a meal, so a fasting glucose test needs 8 to 12 hours without food. Triglycerides rise sharply after eating fat, so a fasting lipid profile gives a more reliable reading, although many laboratories now accept non-fasting cholesterol tests for routine screening. Iron and some hormone tests are also affected by food and time of day.
How long should you fast before a blood test?
Usually 8 to 12 hours, which is why fasting tests are often booked first thing in the morning. Follow the time you are given: fasting for longer than asked does not make the result more accurate and can leave you feeling faint. Water is allowed and helps.
Which blood tests do not need fasting?
A full blood count, kidney and liver function, thyroid function, vitamin D, B12, folate, inflammatory markers such as CRP, and most hormone tests can be done at any time without fasting. HbA1c, the three-month average of blood sugar used to assess diabetes risk, does not need fasting either, which is one reason it has largely replaced fasting glucose for screening.
Fasting blood test rules: what you can and cannot have
Have your last meal the evening before and book a morning appointment. Water is fine and encouraged, as being well hydrated makes the blood draw easier. Avoid tea, coffee, juice, chewing gum and alcohol. Take regular medication unless you have been told otherwise, and if you are diabetic or take medication that must be taken with food, ask before fasting.
If you forget
Tell the person taking your blood. Some tests can still go ahead, others will be flagged as non-fasting on the report so the result is interpreted correctly, and a few will need rebooking. It is far better to say so than to have a misleading result.
At Omnia
When you book Randox blood testing at our clinic in Chiswick, W4, we tell you whether your panel includes any fasting markers and, if it does, offer an early appointment so you are not going hungry for long. Single tests such as vitamin D, B12 and a full blood count need no fasting; health checks such as Omnia Essential and The Complete Man include glucose and cholesterol, so we ask you to fast. See every test and price. If you are booking our cholesterol test (from £39) or HbA1c and diabetes test (£69), we will tell you whether to fast. Book at our blood test clinic in Chiswick: no GP referral is needed and the blood draw usually takes under ten minutes. Omnia Lifestyle is at 8 to 9 Bedford Corner, The Avenue, Chiswick W4 1LZ, close to Turnham Green station, on bus routes 94, E3 and 272. Limited parking is available on request when booking. Early fasting appointments suit clients travelling from Hammersmith, Acton, Isleworth and Hanwell before work.