What would cause fit + in a 45y female with hx of colorectal cancer in remission and hemorrhoid ligation done 6mo ago, last egd+colo in 11/2020 (1 tabular adenoma bx, erosive gastritis), cea 0.7, 2g/dl hgb drop in last 2mo w/o clear bleeding source?

If FIT is positive, source of blood loss is likely from the GI tract, especially you have iron deficiency anemia with that 2 gm Hb loss. Unfortunately, you will need both upper and lower endoscopic studies again. Bleeding from small intestine can happen but it is relatively rare.

A positive FIT test means bleeding in the lower intestine. It does not say anything about what may be causing the bleeding. It is imperative that you consult your doctor.