How recent should lab tests be prior to a colonoscopy?

Laboratory Tests Prior to Colonoscopy

Laboratory tests for colonoscopy should be performed within 3 months prior to the procedure, with comprehensive testing including full blood counts, biochemistry, and serum carcinoembryonic antigen (CEA). 1

General Laboratory Requirements

• A comprehensive physical examination and laboratory tests including full blood counts, biochemistry, and serum CEA must be carried out before decisions on the definitive treatment approach for patients with suspected colorectal cancer 1
• These laboratory tests should be performed within 3-6 months prior to the colonoscopy to ensure the most current assessment of the patient's health status 1
• For routine screening colonoscopies in healthy individuals, recent laboratory tests within 3 months are generally considered adequate 1

Specific Laboratory Considerations

Pre-Procedure Assessment

• Complete blood count is particularly important as it can help identify potential underlying conditions that might be associated with colorectal cancer 2
• An elevated red cell distribution width (RDW) is 84% sensitive and 88% specific for right-sided colon cancer, making it an important parameter to assess 2
• Biochemistry tests should include liver and kidney function tests to assess the patient's overall health status and ability to tolerate the procedure 1

Special Populations

• Patients on anticoagulation therapy require special consideration, with coagulation profiles obtained just before colonoscopy 3
• For patients with suspected colorectal cancer, serum CEA testing is essential as part of the comprehensive laboratory workup 1
• Patients with medical conditions that increase risk of poor bowel preparation (cirrhosis, Parkinson disease, dementia, diabetes, constipation) may require additional assessment 4

Timing Considerations

• Laboratory tests should be performed within a timeframe that allows for appropriate clinical decision-making 1
• For follow-up colonoscopies after a positive FIT test, the procedure should be performed within 6 months, with laboratory tests conducted prior to this appointment 1
• Delays in colonoscopy of more than 6 months after a positive FIT test are associated with higher risks of advanced adenomas, colorectal cancer, and advanced stage disease 1

Common Pitfalls to Avoid

• Failing to discontinue iron supplements at least 7 days before the procedure, as iron residue can compromise diagnostic accuracy 4
• Not obtaining appropriate laboratory tests that could identify patients at higher risk of colorectal cancer (such as those with anemia or elevated RDW) 2
• Delaying colonoscopy for more than 6 months after a positive screening test, which is associated with increased risk of colorectal cancer and advanced disease 1
• Not checking coagulation profiles in patients on anticoagulation therapy, which could increase risk of bleeding complications during biopsy or polypectomy 3

By ensuring laboratory tests are performed within 3 months prior to colonoscopy and include comprehensive assessment of blood counts, biochemistry, and relevant tumor markers when indicated, clinicians can optimize patient safety and diagnostic accuracy during the procedure.