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Preoperative Medical Tests
The series of preoperative medical tests that you will undergo are absolutely essential to your care.
Some of them are standard and apply to all hip replacement patients whilst others will only be carried out if there is some particular concern about a particular aspect of your health: -
An X-ray hip joint (anteroposterior view) - used to measure the size of the head of the femoral component.
- A chest X-ray (particularly for patients with Rheumatoid Arthritis) to rule out infection of the respiratory tract e.g. pneumonia or tuberculosis.
The chest X-ray also shows the size of the heart which is increased in cases of congestive cardiac failure (CCF). If this is detected the surgery will probably be considered as too risky.
- ECG - electrocardiogram which shows the heart's electrical activity is used to detect any silent myocardial ischemia or infarction and will demonstrate arrhythmias.
- Echocardiography - shows the structural and functional capacity of the heart in particular evidence of any valvular diseases and will be carried out if any underlying heart disease is suspected either from a review of your history or on clinical examination.
- Pregnancy testing - the need for this test will depend on the risk to the fetus from the surgery or anaesthetic. One of the main concerns that doctors and anesthesiologists have when operating on a pregnant woman is preterm labor. For this reason, pregnant women are advised to delay surgery until the second or, preferably, third trimester.
- Urea and electrolytes - to check for any underlying renal deficiency. Your kidneys need to be working well to withstand surgery otherwise there is a high risk they will sustain further damage as a result of intra-operative hypotension(caused by blood loss during surgery) and limited urine output. This test is always recommend in patients over 65 years of age.
Moreover significant uremia(poor renal functioning) will result in decreased platelet activity which will in turn increase the amount of blood lost (as it is slow to coagulate).
High urea levels are also immunesuppressive resulting in infections.
- Sickle cell testing (hemoglobin electrophoresis) - this is an essential preoperative medical test for anyone at risk of sickle cell disease (SCD). Patient's with SCD are more likely to undergo a hip replacement (and have it at a younger age) as a result of avascular necrosis of the femoral head.
The image on the right shows normal and sickle shaped blood cells
Because surgery exposes patients to many of the factors that are known to precipitate red blood cell sickling (change of shape), people with SCD undergoing surgery require meticulous clinical care to prevent perioperative sickle cell-related complications such as anemia and localized pain. Sickling is particularly dangerous if it occurs during surgery as these abnormally shaped cells may cling to the vessels and cause pulmonary hypertension and stroke.
- Liver function test - this checks for underlying malnourishment and jaundice. If the patient is malnourished then healing will be delayed and there is high morbidity and mortality (sickness and death) in malnourished people undergoing surgery.
Patients with jaundice normally have decreased appetite and nausea this, combined with a tendency to vomit, results in dehydration. Surgery (and anesthesia) are not recommended for patients who are dehydrated as it can result in further deterioration of the kidneys.
- Serum potassium assays (tests that measure potassium levels in the blood)- in patients using diuretics or with a history of cardiac arrhythimia.
Diuretics decrease the potassium levels in the blood as they cause an increase in the amount of potassium excreted through the kidneys in urine. Potassium plays an important role in maintaining the rhythm of the heart. If potassium levels are low or high then heart activity is irregular and arrhythmia occurs.
- Urinalnaysis - to check for undiagnosed diabetes or urinary tract infection Wound healing is significantly delayed by diabetes.
If the patient is diabetic their blood glucose levels will need to be monitored throughout the procedure and a continuous infusion of insulin given.
Any infection present can spread to other parts of the body during surgery and an infected implant is very difficult to deal with. This is one of the essential preoperative medical test
- Clotting - particularly important for people who take aspirin or warfarin or who have a known clotting disorder. Aspirin is an antiplatelet drug and warfarin is an anticoagulant. That is they function as a blood thinner (aspirin)or increase clotting time (warfarin). It is important that the surgeon is aware of the clotting capacity of the patient's blood.
- Group and save (hold) - if the likelihood of needing a blood transfusion is low than your blood will be only be grouped. Serum is also checked for antibodies.
- Cross match - with cross matching a sample of the patient's blood is mixed with a sample of donated blood to see if any transfusion reaction occurs.
For a hip replacement both grouping and cross matching are done and a minimum of two pints of blood prepared for transfusion.
- FBC - Full Blood count - to check for anemia which can increase the risk of intra-operative hypoxia (lack of oxygen) or increased cardiac workload. Anemaia is also associated with increased risk of myocardial infarction or a cerebrovascular event.
Which Preoperative Medical Tests Do All Hip Replacements Patients Have?
In general all hip replacement patients will have: -
- An X-ray hip joint(anteroposterior view)
- A chest X-ray
- Sickle cell testing (hemoglobin electrophoresis)
- Urea and electrolytes
- Pregnancy testing (for women of child-bearing age only)
- Serum potassium assays
But this may vary between countries and with different surgeons so don't be surprised if your preoperative medical tests are slightly different.
I hope this explanation of why you need to undergo so many preoperative medical tests has been useful.
Personally I found it reassuring to know that the surgical team was looking out for so many possible things that could go wrong and, of course, reassuring when they didn't find any. I hope that's the same for you too.
It was the National Joint Registry of Australia that first voiced concerns about the Depuy ASR implant that has recently been recalled.
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