Pre-operative assessment

Last updated: Friday, 28, January, 2011
Key InformationAppropriate 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 ( LFT ). 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 (e.g. 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 (e.g. digoxin levels, potassium, and thyroid function).

Significant risk of hypotension

FBC, urea, creatinine, electrolytes, LFT.

Significant Risk of Major Blood Loss (e.g. major vascular procedures)

FBC, urea, creatinine, electrolytes, LFT, PT, APPT, platelet count.

Cardiovascular Disease

FBC, urea, creatinine, electrolytes (potassium within one week if on digoxin or diuretics). Digoxin levels if indicated.

Hepatic Disease

LFT, PT, and Hepatitis B and C as appropriate.

Renal disease

Urea, creatinine, electrolytes, FBC.



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 – venous.

Post-anaesthetic apnoea

See Apnoea-post-anaesthetic

Malignant hyperthermia

Specialist physiological investigation with muscle biopsy. CK alone is not sufficient.

Diabetes mellitus

Urea, creatinine, electrolytes, blood glucose on day of surgery.

Thyroid Disease     


See Hyperthyroidism and Hypothroidism

Malignancy, chemotherapy or radiation therapy  

FBC and, for disseminated malignancy, LFT and PT.

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   

FBC. Assess suitability as a donor. See Blood transfusion, doner testing.