•A 55 y/o man presents with shortness of breath on exertion. Laboratory studies reveal iron deficiency anemia. Patient was started on Iron pills orally. The patient consumes a lot of red meat and was surprised to know that he was iron deficient. Fecal occult blood testing revealed a positive stool guaic. A colonoscopy and EGD were subsequently performed which were absolutely normal. A repeat Guaic was performed and was found to be negative. A further investigation for the cause of iron deficiency in this patient revealed celiac disease leading to iron malabsorption. What is the most likely cause of positive Guaic in this patient? •
A. Obscure GI Bleeding
B. Celiac disease
C. False positive from red meat
D. False positive from Iron pills
E. Colon cancer
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C??
I would pick C as it seems reasonable. But what about B. Doesnt celiac disease also involve Fe malabsorbtion and loss?
c
could be both iron and red meat- confusing question
Answer c meat can cause false positive FOBT iron could not produce FOBT positive. Myoglobin in red meat can case FOBT positive..
C
c
C
Myoglobin causes guaic +ve stool
Ans. C
Red meat can lead to false positive guaic as it may oxidize the guaic reagent ( Vitamin C on the other hand, anti-oxidizes it and causes false –ve guaic.)
Obscure bleeding ( Ans. A) is possible but in this patient the most likely cause for iron deficiency was already established as celiac disease making intermittent obscure bleeding less likely.
Celiac disease ( Ans. B) does not cause False +ve Guaic.
Iron pills ( Ans. D) can cause black discoloration of the stool but not a false positive guaic.
The fact that the colonoscopy was normal makes bleeding from colon cancer ( Ans. E)unlikely here.