Background: The majority of colorectal cancer cases are diagnosed following symptomatic presentation in the United Kingdom.

Aim: To identify windows of opportunity for timely investigations or referrals in patients presenting with colon and rectal cancer-relevant symptoms or abnormal blood tests.

Design and setting: Retrospective cohort study using linked primary care and cancer registry data of colorectal cancer patients diagnosed in England between 2012-2015.

Methods: Monthly consultation rates for relevant clinical features (change in bowel habit, rectal bleeding, abdominal pain, mass, constitutional symptoms, and other bowel symptoms) and abnormal blood test results (low haemoglobin, high platelets and inflammatory markers) up to 24 months pre-diagnosis were calculated. Poisson regression adjusted for age, sex and relevant comorbidities was used to estimate the most likely month when consultation rates increased above baseline.

Results: 5033 colon and 2516 rectal cancer patients were included. Consultations for all examined clinical features and abnormal blood tests increased in the year pre-diagnosis. Rectal bleeding was the earliest clinical feature to increase from baseline rate: 10 months (95%CI 8.3-11.7) pre-diagnosis for colon cancer; 8 months (95%CI 6.1-9.9) for rectal cancer. Low haemoglobin, high platelets and inflammatory markers increased from as early as 9 months pre-diagnosis.

Conclusion: Our study found evidence for early increase in rates of consultation for relevant clinical features and abnormal blood tests in patients with colorectal cancer, suggesting that earlier instigation of cancer-specific investigations or referrals may be warranted in some symptomatic patients.