Detection of chronic gastro-intestinal bleeding using Cr-51 labeled RBC, and improving localization using 99mTc RBC scintigraphy

Objectives To demonstrate the usefulness of ⁵¹Cr- labeled RBC to detect and quantify significant occult GIT blood loss to improve the sensitivity of ^99mTc- labeled RBC to localize bleeding site with blood loss > 50mls.

Methods Retrospective study from 2002 to 2005,with ethics approval. RBC labeled with 6- 10 MBq ⁵¹Cr-sodium chromate was injected intravenously. 5ml blood was taken after 30 minutes to prepare standard, and on alternate days to determine clearance. Stool was collected for 21 days. Stool, standard and blood were counted in a whole body counter.Blood loss in stools were calculated by dividing blood sample in grams by counts in blood multiplied by stool count, then dividing the blood density (1.05ml/g) to quantify blood loss in milliliters. Normal stool blood loss is 0.5-4ml/d.When blood loss exceeded 50ml/d, a ^99mTc – labeled RBC was done

Results 23 studies done in 22 patients(1 patient had 2 studies) .17 studies positive for occult blood loss, 5 normal, 1 false positive ( menstruation). No imaging was done in 9 with blood loss <50ml . Imaging in 8 with >50ml of blood loss, located bleeding site in 5.

Conclusions ⁵¹Cr-labeled red blood cells studies provide a useful method to detect and quantify significant occult GIT blood loss in chronic iron deficiency anaemia with no clinical cause.The sensitivity of localizing the bleeding site with ^99mTc-labeled RBC scintigraphy was improved with occult blood loss > 50mls.