Preoperative blood tests
Informed by recognized medical guidance
Overview
Preoperative blood tests are blood tests that you have before surgery. They help your healthcare team check your general health, find any hidden problems, and make sure it is safe for you to have the operation.
Key facts
- These tests are a routine part of preparing for most surgeries.
- They can check for anaemia (low red blood cells), infection, and how well your blood clots.
- Results help your doctor plan the safest type of anaesthesia and any extra care you might need.
- The tests are usually done in the weeks or days before your operation.
Yes, preoperative blood tests are very common. Most people who have surgery will have at least some blood tests beforehand.
Preoperative blood tests are recommended for anyone scheduled to have surgery, especially for major procedures, and more often for older adults, people with long-term health conditions, or those taking certain medications.
Symptoms
- If you are about to have surgery and you develop severe chest pain, difficulty breathing, or a high fever, call your local emergency number immediately.
- ⚠If you notice new or worsening symptoms like heavy bleeding, bruising, or signs of infection (redness, pus, fever) in the days before your surgery, contact your surgical team or GP the same day.
Common symptoms
- You may not have any symptoms – the test is done to look for hidden issues.
- If you have symptoms like feeling very tired, pale skin (anaemia), or easy bruising/bleeding, your doctor may want to check your blood before surgery.
Symptoms in children
- Children may need preoperative blood tests before surgery, especially if they have a chronic condition or are having a major operation.
Symptoms in older adults
- Older adults more often have conditions like anaemia or kidney problems that can affect surgery, so blood tests are especially important for them.
Causes
Main causes
- Preoperative blood tests are not caused by a disease – they are scheduled to prepare for surgery.
- However, certain health conditions (like heart disease, diabetes, or anaemia) make these tests especially important.
Risk factors
- Being over 65 years old
- Having a long-term illness such as diabetes, kidney disease, or a blood clotting disorder
- Taking medicines that affect bleeding, such as blood thinners
- Having had problems with surgery or anaesthesia in the past
When to see a doctor
See a doctor urgently if:
- Contact your surgical team or GP urgently if you have a fever, feel very unwell, or have unexpected bleeding or bruising before your surgery.
Book a routine appointment if:
- See your healthcare provider as scheduled for your preoperative assessment – this is when blood tests are usually ordered.
Diagnosis
Preoperative blood tests are not used to diagnose a condition – they are screening tests to check your health before surgery. Your doctor will review the results to see if any adjustments are needed.
Tests that may be done
- Full blood count (FBC) – checks for anaemia, infection, and how well your bone marrow is working
- Clotting tests (coagulation screen) – assess your blood's ability to clot
- Kidney function tests (urea and electrolytes) – measure how well your kidneys work
- Liver function tests – check your liver health
- Blood glucose test – checks your sugar level
- Pregnancy test – sometimes done for women of childbearing age
What to expect at your appointment
A healthcare professional will take a small sample of blood from a vein in your arm using a needle. It takes a few minutes and may cause a brief pinch. Results are usually available within a day or two. Your surgical team will discuss them with you before the operation.
Treatment
If the blood test results show a problem, the treatment focuses on making you as safe as possible for surgery. This can include treating the underlying issue, adjusting your medicines, or sometimes delaying the operation.
Self-care at home
- Stay well hydrated before your tests and surgery (unless instructed not to drink).
- Eat a balanced diet to support your overall health.
- Tell your healthcare team about any medicines or supplements you take.
Medical treatments
Depending on the test results, your doctor may recommend treatments such as iron supplements for anaemia, stopping or adjusting blood-thinning medicines, starting antibiotics for an infection, or getting a blood transfusion if you are very anaemic. These decisions are always made with your safety in mind.
When is surgery considered?
In most cases, surgery goes ahead as planned once any issues from the blood tests are managed. If the risks are too high, the surgery may be postponed until the problem is resolved.
Living with this condition
Preoperative blood tests are a one-time event; they do not affect your daily life after surgery except to improve your safety. If a condition is found, you may need ongoing follow-up.
Lifestyle tips
- Follow any pre-surgery instructions given by your healthcare team.
- If you have a chronic condition, keep managing it well with your doctor's advice.
Diet and exercise
Maintain a healthy diet and regular physical activity as you are able before surgery, as this can help with recovery. Your doctor may give specific advice if your blood tests show anaemia or other issues.
Mental health and emotional wellbeing
Waiting for surgery and test results can be stressful. It is normal to feel anxious. Talk to your healthcare team about any worries – they are there to support you.
Prevention
Preoperative blood tests are not something to prevent – they are a safety measure. However, you can help by keeping your general health in good shape, managing chronic conditions, and attending all preoperative appointments.
Complications
If left untreated
- If a problem found by the blood tests is not treated, surgery may be riskier – you could have more bleeding, a longer recovery, or complications like heart problems.
- Untreated anaemia can cause fatigue and poor healing after surgery.
Long-term outlook
The outlook after preoperative blood tests is very good. These tests are done to catch issues early so your surgery can be as safe as possible. Most people have no problems and their operation goes ahead without delay.
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Always verify with your doctor
Health guidelines vary by country and region. The information in this article is based on international clinical guidelines but may not reflect the specific guidelines, medications, or practices in your country. Always discuss your health concerns with your own doctor or healthcare provider, and refer to your local national health guidelines where available.
Important notice This information is for educational purposes only. It does not replace professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider about your specific situation. If you are experiencing a medical emergency, call your local emergency services immediately.
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Sources and guidance
This article is educational and is prepared with reference to recognized health information and clinical guidance sources where available. Specific source links may vary by topic.
Last updated: July 16, 2026
Educational note: This information is for education only and is not a diagnosis.
Use it to support, not replace, advice from a licensed clinician.
If symptoms are severe, worsening, or urgent, call your local emergency number or seek emergency care.
Guidance may differ by country or region. Confirm local recommendations with a qualified healthcare provider.