What Tests Will I Need Before Knee Replacement Surgery?

Key Takeaways

• Pre-operative tests help confirm your surgical plan, assess your fitness for anaesthesia and identify any health issues that should be managed before knee replacement.
• The specific tests you need depend on your health, medications and surgical plan, and may include imaging, blood tests, heart checks and an anaesthetic assessment.
• Abnormal test results do not automatically delay surgery, but they may require treatment or further review to help reduce avoidable risks.
• Preparing for your pre-admission appointments with your medical information, imaging and questions can help make the process smoother and support a well-planned operation.

Once a date is set for knee replacement, most patients are handed a list of appointments, blood tests and scans that can feel more overwhelming than the surgery itself. It is easy to see pre-operative testing as a bureaucratic hurdle, a box-ticking exercise standing between you and the operation you have already decided to have. That framing misses what these tests are actually doing.

Pre-operative testing serves three genuinely important purposes. It confirms and refines the surgical plan for your specific knee, it checks that you can safely undergo anaesthesia and surgery, and it identifies anything that would benefit from treatment or optimisation beforehand, reducing avoidable risk during and after the operation. Not every patient needs every test. What you are asked to complete depends on your age, general health, current medications and the specific requirements of your surgeon and hospital.

This article works through the main categories of pre-operative testing for knee replacement, what each test is actually checking for, and what tends to happen if a result comes back outside the expected range.

Why Tests Are Needed Before Knee Replacement

Pre-operative tests fall into a few broad categories, each serving a different purpose. Some tests assess the knee itself, confirming the diagnosis and helping plan the specific surgical approach. Others assess your general medical fitness for anaesthesia and surgery, checking organs such as your heart, kidneys and liver, and screening for conditions that could affect your safety during the procedure. Some tests specifically screen for infection risk, since infection is one of the more serious complications of joint replacement and is taken very seriously in surgical planning. Finally, some appointments are less about testing and more about medication review and practical preparation for your recovery.

Understanding which category a particular test falls into helps make sense of why it has been requested, rather than experiencing the whole process as an undifferentiated list of appointments.

If you are preparing for knee replacement surgery, understanding the procedure itself can make the pre-operative testing process feel more purposeful. Learning how imaging, blood tests, anaesthetic review and medical optimisation all support surgical planning can help you see these steps as part of preparing for a safer operation and a smoother recovery, rather than simply paperwork to complete before admission.

Tests That Assess the Knee Itself

Imaging of the knee is central to surgical planning, and several types may be used depending on your specific situation.

• Weight-bearing x-rays, also called standing x-rays, are typically the primary imaging test, showing the knee under normal load-bearing conditions and revealing the extent and pattern of joint space narrowing.
• Long-leg alignment x-rays, capturing the entire leg from hip to ankle while standing, may be used to assess overall alignment, particularly relevant if deformity is present or if osteotomy is being considered alongside knee replacement options.
• MRI may be requested if there is uncertainty about the diagnosis, or if your surgeon needs a clearer picture of soft tissue structures such as the anterior cruciate ligament (ACL) or meniscus, particularly relevant when partial knee replacement is being considered.
• CT scans are commonly used for robotic-assisted or computer-navigated surgical planning, providing detailed bone imaging to build a three-dimensional model of your knee, and may also be used for complex deformity or previous surgery.

If you have had recent imaging already, it is worth bringing this to your appointments, since it may reduce the need for repeat scans.

These build on the imaging that confirmed your knee osteoarthritis and guided the plan for knee replacement.

Blood Tests Before Surgery

Blood tests provide a broad snapshot of your general health and help identify anything that needs attention before surgery proceeds.

• Full blood count, checking for anaemia or other blood abnormalities that could affect surgery and recovery.
• Electrolytes and kidney function tests, since these organs need to handle the physiological demands of surgery and anaesthesia.
• Liver function tests, relevant to how your body processes anaesthetic medications.
• Blood glucose or HbA1c testing is particularly important if you have diabetes or risk factors for it, since well-controlled blood sugar supports better wound healing and reduces infection risk.
• Clotting profile, assessing how your blood clots, which is relevant both to surgical bleeding risk and to your risk of blood clots such as deep vein thrombosis, after surgery.
• Blood group and antibody screening, sometimes performed in case a blood transfusion is needed, though this is uncommon for routine knee replacement.

Heart and Lung Checks

Given the physiological demands of surgery and anaesthesia, your heart and lung health are an important part of pre-operative assessment, particularly if you have any relevant history.

An electrocardiogram (ECG) records the electrical activity of your heart and may be requested, particularly for older patients or those with any history of heart disease, to check for underlying rhythm or conduction issues. A chest x-ray may be requested where indicated, generally for patients with relevant respiratory history or specific risk factors, rather than as a routine test for every patient. If you have known heart disease, a cardiology review may be arranged to ensure your heart is optimally managed before surgery. Similarly, if you have significant lung disease or sleep apnoea, a respiratory review may be arranged, since these conditions can affect how anaesthesia and sedation are managed during and after your procedure.

Urine Tests and Infection Screening

Because infection is one of the more serious potential complications of joint replacement, screening for infection risk is a genuine priority in pre-operative preparation.

A urine test may be requested to check for a urinary tract infection, since an untreated infection elsewhere in the body can increase the risk of infection affecting the new joint. Depending on your specific hospital’s protocol, screening for methicillin-resistant Staphylococcus aureus (MRSA) or methicillin-sensitive Staphylococcus aureus (MSSA) may also be performed, generally through a simple swab, since identifying and treating these bacteria beforehand can reduce infection risk. Your surgical team may also check for any skin infections or wounds near the surgical site, and may recommend addressing significant dental issues beforehand, since dental infections have a recognised, if uncommon, link to prosthetic joint infection risk.

Medication Review

A thorough review of your current medications is an important part of preparation, since several common medications need specific management around the time of surgery.

• Blood thinners, which may need to be temporarily adjusted or stopped before surgery under your surgical team’s specific guidance, balancing bleeding risk against your reason for taking the medication.
• Anti-inflammatory medications, which are sometimes advised to be stopped for a period before surgery due to their effect on bleeding and clotting.
• Diabetes medications, which may need adjustment around your fasting period and surgery date.
• Supplements, including some herbal or over-the-counter products, can affect bleeding or interact with anaesthetic medications.

Never stop or adjust any medication independently based on general information. Always follow the specific instructions given by your surgeon, anaesthetist or GP, since the right approach depends on your individual medications and health conditions.

Anaesthetic Assessment

A pre-admission clinic appointment, either in person or over the phone, generally includes a review by or on behalf of your anaesthetist, covering your medical history, current medications, allergies and any previous anaesthetic reactions or complications. This is also where fasting instructions are confirmed, and where you can discuss the specific anaesthetic approach planned for your surgery, whether that involves spinal anaesthesia, general anaesthesia, or a combination.

This appointment is a genuine opportunity to raise any concerns or questions about the anaesthetic process, rather than something to get through quickly, since a clear understanding beforehand generally reduces anxiety on the day itself.

Medical Clearance or Physician Review

For patients with more complex medical histories, additional review by a physician or specialist may be arranged before surgery is confirmed. This is more likely if you have diabetes, heart disease, kidney disease, a higher BMI, complex medication regimens, or a previous history of blood clots.

This additional review is not intended to prevent surgery, but to ensure any relevant conditions are as well managed as possible beforehand, reducing avoidable risk during your procedure and recovery. Your GP often plays a coordinating role in this process, particularly for patients managing multiple health conditions.

Physiotherapy and Functional Assessment

Beyond medical testing, preparation often includes a physiotherapy or functional assessment, sometimes described as prehabilitation, focused on strengthening the muscles around your knee before surgery and reviewing your current walking pattern, use of any walking aids, and ability to manage stairs.

This appointment may also cover practical discharge planning, including your home environment, any equipment you might need, such as a raised toilet seat or shower chair, and organising support for the first one to two weeks after surgery. Patients who go into surgery with better baseline strength and a clear recovery plan in place often progress through early rehabilitation more smoothly.

This is also where pre-operative rehabilitation and physiotherapy begin, so you enter surgery as strong as possible.

What Happens if a Test Result Is Abnormal?

An abnormal test result does not automatically mean your surgery will be cancelled. In many cases, it simply means a specific issue needs to be addressed or better managed before proceeding, such as adjusting diabetes medication to improve blood glucose control, treating a urinary tract infection before surgery, or arranging a brief cardiology review to optimise a heart condition.

In some cases, surgery may be delayed briefly while an issue is treated or clarified, which, while frustrating, is generally in your best interest, since proceeding with an unaddressed risk factor can increase the chance of complications. Your surgical and anaesthetic team will discuss any abnormal results with you directly and explain what, if anything, needs to happen before your surgery date is confirmed or adjusted.

Australian Pathway: GP, Specialist, and Hospital Coordination

Your general practitioner (GP) often plays a coordinating role throughout this process, particularly for ordering initial tests, coordinating specialist reviews for complex health conditions, and communicating with your surgical team. Many pre-operative blood tests and standard imaging are covered by Medicare with an appropriate referral, though specific rebates depend on the type of test and current guidelines. In the private system, your surgeon’s rooms or the hospital’s pre-admission clinic will generally coordinate the required tests and appointments, and you should receive informed financial consent outlining any anticipated costs, including anaesthetist fees, before your admission date. In the public system, these tests and reviews are arranged as part of your overall hospital care under Medicare, coordinated by the hospital’s pre-admission team.

Most pre-operative tests are covered through Medicare or the hospital, though some may carry a gap.

Practical Checklist Before Your Pre-Admission Appointment

Arriving prepared for your pre-admission appointments helps the process run smoothly and reduces the chance of delays.

• A current list of all medications and supplements, including doses.
• Any known allergies, including previous reactions to medications or anaesthesia.
• Existing imaging, such as X-rays, MRI or CT scans, even if taken some time ago.
• Reports or letters from your GP or other specialists managing relevant health conditions.
• A list of any questions or concerns you would like to raise about your tests, anaesthesia or surgery.

Frequently Asked Questions (FAQs)

1. What tests are done before knee replacement surgery?

Common tests include weight-bearing x-rays of the knee, blood tests such as a full blood count and kidney and liver function tests, and an anaesthetic assessment. Additional tests, such as an ECG, chest x-ray, urine test, MRI or CT scan, may be added depending on your individual health, age and surgical plan.

2. Do I need blood tests before knee replacement?

Yes, blood tests are a routine part of pre-operative preparation for most patients, helping to assess general health, blood counts, organ function and clotting status before surgery and anaesthesia.

3. Why do I need an ECG before surgery?

An ECG checks the electrical activity of your heart and can identify underlying rhythm or conduction issues that may be relevant to anaesthetic safety. It is more commonly requested for older patients or those with a relevant medical history, rather than for every patient.

4. Do I need an MRI before knee replacement?

Not always. Many patients with clear, advanced arthritis on X-ray do not require an MRI. It becomes more relevant when there is diagnostic uncertainty, suspected ligament or meniscus injury, or when partial knee replacement is being considered and further soft tissue detail is needed.

5. Why do I need standing X-rays?

Standing, or weight-bearing, x-rays show the knee joint under normal load-bearing conditions, revealing the true extent of joint space narrowing more accurately than an x-ray taken while lying down.

6. Will abnormal blood tests delay my surgery?

Not necessarily. Many abnormal results can be addressed through treatment or medication adjustment without significantly delaying surgery. In some cases, a short delay is recommended to properly manage a specific issue, which generally reduces your overall risk rather than simply being a bureaucratic hold-up.

7. Do I need to stop blood thinners?

This depends on your specific medication and the reason you are taking it, and should only be adjusted under the specific guidance of your surgical or anaesthetic team. Never stop or adjust blood thinners independently based on general advice.

Conclusion

Pre-operative testing before knee replacement is not simply paperwork to get through. Each test and appointment serves a specific purpose, whether that is confirming the diagnosis and planning your surgery, checking that you can safely undergo anaesthesia, screening for infection risk, or identifying a health issue worth managing beforehand. Not every patient needs every test, and the specific combination required for you depends on your age, health, medications and surgical plan.

If you are ever unsure why a particular test has been requested, it is entirely reasonable to ask your surgeon, anaesthetist or GP directly what that test is checking for and how it fits into your overall surgical plan. Understanding the purpose behind each step tends to make the whole process feel considerably less bureaucratic and considerably more like what it actually is: careful preparation for a safe and well-planned surgery.

The exact tests depend on your health and the hospital’s protocol. Book a consultation with our Sydney knee team to understand what your pathway involves.