Before surgery
Common Tests Before Surgery
Before an operation your team may order a few tests. They're routine — done to make your anesthetic and surgery as safe as possible and tailored to you, not because something is wrong. Here's what each common test checks, in everyday language.
The short version
Why you have tests before surgery
Tests give your anesthetist and surgeon a clear, up-to-date picture so they can keep you safe and plan the right anesthetic. They pick up things worth knowing in advance — like low iron, a kidney or clotting issue, or an irregular heartbeat — so these can be managed before the day rather than discovered during surgery. National guidance (such as the UK's NICE and the American Society of Anesthesiologists) tells teams to order only the tests that are actually useful for your situation, which is why not everyone gets the same ones.
Blood tests
A small blood sample can cover several checks at once:
- Full blood count (FBC / CBC) — looks for anemia (low red cells, common and easily treated), signs of infection, and your platelet level (important for clotting).
- Kidney function & electrolytes (U&E) — checks your kidneys and salts like sodium and potassium, which affect how your body handles anesthetic and fluids.
- Clotting / coagulation (INR) — how well your blood clots, especially important if you take a blood thinner like warfarin.
- Blood glucose / HbA1c — blood sugar and longer-term diabetes control, so your sugars can be managed around surgery.
- Group & save / crossmatch — finds your blood type and checks for antibodies, so matched blood is ready if a transfusion is ever needed. Routine for bigger operations; it doesn't mean one is expected.
- Liver function (LFTs) — sometimes added if relevant to your health or medicines.
ECG (heart tracing)
An ECG records your heart's rhythm through small sticky pads on your chest — it's quick and completely painless. It's commonly done for older adults, anyone with heart symptoms or conditions, or before larger operations, to give the team a baseline of how your heart is behaving.
Chest X-ray
A chest X-ray is not routine for everyone. It's ordered when there's a specific reason — for example new breathing or heart symptoms, certain chest or major operations, or to follow up a known lung condition. If you don't need one, you won't have one.
Pregnancy test
Anyone who could be pregnant is usually offered or asked to take a quick urine pregnancy test, often on the day. It's there because anesthesia, some medicines, and X-rays can affect an early pregnancy — so it's a safety step, kept confidential.
MRSA swab
A painless swab (usually inside the nose) checks whether you carry MRSA, a common skin bacterium that many healthy people have without being ill. If it's found, you're given a simple wash and nasal cream for a few days beforehand to lower the chance of a wound infection. A positive swab is not an infection and rarely changes your surgery date.
Tests you might have for specific reasons
- Echocardiogram — an ultrasound of the heart's pumping, if a heart problem is suspected.
- Lung (pulmonary) function tests — breathing tests for significant lung disease or major chest surgery.
- Sleep study / oximetry — if obstructive sleep apnea is suspected, as it affects anesthesia planning.
- COVID or other swabs — only where your hospital still requires them; policies vary, so follow your pre-op letter.
Getting ready for your tests
- Most tests need no special preparation — just turn up. Your letter will flag any that need fasting.
- Bring an up-to-date list of your medicines (including inhalers, patches, supplements and anything over-the-counter).
- Mention if you might be pregnant, have a needle phobia, or have had reactions to tests before.
- Results go straight to your surgical and anesthetic team — you usually don't need to chase them, but you can always ask.
Want to know which tests apply to you?
Frequently asked questions
Do I need to fast for pre-op blood tests?
Usually no — most pre-operative blood tests don't need fasting. The exception is a fasting glucose or certain metabolic tests, where you may be asked not to eat beforehand. Your pre-op letter will say if fasting is needed. Don't confuse this with surgery-day fasting, which is separate.
How long are pre-op tests valid before surgery?
It varies by test and your health, but as a rough guide many routine blood tests and an ECG are accepted for about 3 months if your health is stable. A 'group & save' (blood type) and some tests can have a shorter window. If your surgery is delayed, your team may repeat them — follow their timing.
Why do I need a pregnancy test before surgery?
Anyone who could be pregnant is usually offered or asked to have a urine pregnancy test on the day, because anesthesia, some medicines, and X-rays carry risks in early pregnancy that change the plan. It's routine and confidential — not an assumption about you.
What happens if a test comes back abnormal?
Most 'abnormal' results are minor and don't stop your surgery — they just help your team plan (for example, treating low iron, adjusting a medicine, or adding monitoring). Occasionally a result means a test needs repeating or surgery is delayed until it's sorted, which is done for your safety. Your team will explain and tell you the next step.
Do I need all of these tests?
No. Most people don't get every test. What you need depends on your age and health and on how big the operation is — a fit person having a minor procedure may need few tests or none, while major surgery or ongoing conditions mean more. Your team follows national guidance to order only what's useful.
What is an MRSA swab and does it mean I'm infected?
No. An MRSA swab (usually of the nose, sometimes the groin or skin) just checks whether you carry a common bacterium called MRSA on your skin — many healthy people do, with no illness. If it's positive you're given a simple wash and nasal cream for a few days before surgery to lower the chance of a wound infection.