Pre-operative assessment

Key Information

Appropriate Tests


The need for pre-operative laboratory investigations should be directed by:

  • The patient’s known medical conditions.
  • The findings of a thorough clinical history and physical examination.
  • The potential intra- and post-operative complications of the proposed surgery and the anaesthesia.

Investigations should be individualised to the patient for specific clinical indications, balancing the patient’s clinical status with the potential risks of anaesthesia and surgery.

Routine screening of healthy patients for low risk surgery is generally not indicated. For low risk surgery, unless there has been a change in clinical status, many previously normal tests need not be repeated within 4 months; exceptions include potassium in those taking diuretics and blood glucose in diabetics.

Anaesthesia and surgery have the potential to cause serious hypoxaemia and hypotension, resulting in cerebral, cardiac, renal and hepatic injury. The most commonly performed preoperative laboratory investigations are therefore those that establish oxygen carriage (Hb) and the status of organs most at risk, in particular the kidneys (UE) and liver (Liver function tests). The status of both kidney and hepatic function may also be important because of the metabolism/excretion of anaesthetic drugs by these routes, as well as the frequent administration of drugs known to be nephrotoxic (eg, NSAID, gentamicin).

The peri-operative period is also one in which autonomic dysfunction is common. Therefore, if suggested by history, abnormalities that compound the risk of cardiac instability, in particular arrhythmia, should be identified (eg, Digoxin level, Potassium, and Thyroid function).

Significant risk of hypotension

Full blood count, Urea, Creatinine, Electrolytes, Liver function tests.

Significant risk of major blood loss (e.g. major vascular procedures)

Full blood count, Urea, Creatinine, Electrolytes, Liver function tests, Prothrombin time, APTT, Platelet count.

Cardiovascular disease

Full blood count, Urea, Creatinine, Electrolytes (Potassium within one week if on digoxin or diuretics). Digoxin level if indicated.

Hepatic disease

Liver function tests, INR, and Hepatitis B and Hepatitis C as appropriate.

Renal disease

Urea, Creatinine, Electrolytes, Full blood count.


Full blood count.

Bleeding history

See Bleeding disorders [aspirin is not an indication for coagulation tests]

Venous thromboembolism

Consider an inherited or acquired predisposition to venous thrombosis. See Thrombosis.

Post-anaesthetic apnoea

See Apnoea post-anaesthetic

Malignant hyperthermia

Specialist physiological investigation with Muscle biopsy. Creatine kinase alone is not sufficient.

Diabetes mellitus

Urea, Creatinine, Electrolytes, blood Glucose on day of surgery.

Thyroid disease

Thyroid stimulating hormone.

See Hyperthyroidism and Hypothyroidism

Malignancy, chemotherapy or radiation therapy

Full blood count and, for disseminated malignancy, Liver function tests and INR.

HIV infection

HIV testing considered. Specific consent will be required from the patient.


Potassium; Magnesium may be requested for arrhythmias.

Anticoagulants (either currently taking or being considered)

See Anticoagulant monitoring

Autologous transfusion being considered

Full blood count. Assess suitability as a donor. See Blood transfusion, donor testing.

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