A population-based study on time trends of hemoglobin in primary care comparing prediagnostic colorectal cancer patients vs age- and sex-matched controls.

Background: Some 40% of colorectal cancer (CRC) patients present with anemia. Temporal trends of gradually decreasing Hb are suggested as a supplementary diagnostic tool for CRC. We set out to explore this concept in a strictly defined population.

Methods: A laboratory database identified patients ≥40 years that had ≥1 Hb test reported from primary care, Örebro county in 2000-17. Linkage to the Swedish Colorectal Cancer Registry identified patients diagnosed with CRC. Other primary care patients served as controls (1:10), matched by age and sex. Prediagnostic Hb in cases and controls were compared and temporal trajectories of Hb modelled using a nonlinear three-parameter logistic function.

Results: 1,534 CRC patients and 15,333 controls were identified. The average number of reported Hb tests in primary care per year increased successively, and diagnostic delay from detection of anemia to diagnosis of CRC decreased; in 2015-17 it was median 4 (IQR 2-6) months. No association was found between last Hb and stage of right-/left-sided colon, or rectal cancer.A statistically significantly lower Hb in CRC patients was discernable 609 days (20 months) prior to diagnosis for men and 905 days (30 months) for women, both in the range of normal Hb. The frequency of Hb testing in the general population primary care was surprisingly low, and was ≥50% annually only in octogenarians.

Conclusion: The findings indicate a potential for Hb trends to inform the diagnostic process of CRC but whether it will translate into any clinical advantage is yet uncertain.