Variations in hemoglobin before colorectal cancer diagnosis.

We have conducted the present case-control study to examine whether long-term variations in blood hemoglobin (Hb) levels within the normal range could detect subtle gastrointestinal bleeding in the early development of colorectal cancer (CRC). A total of 1074 CRC cases aged 45-75 years that have been diagnosed with CRC and had normal Hb levels were frequency matched for age and sex with cancer-free individuals at a ratio of 10 controls per case. Our retrospective analysis indicates that starting from 4 years prior to cancer diagnosis, a progressive significant (P<0.001) decrement in Hb levels (0.28 g/dl per 6 months) was found among cases but not among controls. CRC patients were characterized in an on-going, long-term, logarithmic decrement in Hb levels. Such small changes within the normal Hb range could be missed by health providers, but automatically detected by computerized alert algorithms..