MEASUREMENT OF OCCULT UPPER GASTROINTESTINAL-TRACT BLOOD-LOSS - A DIRECT COMPARISON OF RADIOCHROMIUM AND HEME-PORPHYRIN ASSAY TECHNIQUES

Faecal haem-porphyrin assay by the HemoQuant(TM) method has many pract ical advantages over the well-validated, radiochromium (Cr-51-tagged r ed cell) method for measuring gastrointestinal blood loss. Because hae m may be absorbed but the chromic ion is not, the two measures were di rectly compared in low-grade bleeding from the proximal gastrointestin al tract. Blood loss was measured by both methods simultaneously in 40 patients with osteoarthritis before and during medication with aspiri n preparations. Mean (geometric) daily blood loss before aspirin usage measured 0.60 mL by radiochromium (range 0.13-1.62) and 0.47 mL (0.14 -1.40) by HemoQuant(TM) (P = 0.042). On aspirin, bleeding rose to 1.57 mL/day (0.43-4.85) by radiochromium and to 0.72 mL/day (0.23-3.0) by HemoQuant(TM) (P < 0.0001). The two measures correlated well, r = 0.84 7 (P much less than 0.0001), but the regression coefficient was 0.417, reflecting the lower estimates of bleeding by HemoQuant(TM). In four normal subjects who ingested Cr-51-labelled red cells (26-41 mL) over 3 days, recovery of Cr-51 was complete (103 +/- 2%, +/- s.e.), but rec overy of haem-porphyrins was only 63 +/- 13% (P = 0.01), presumably be cause of absorption of haem. Although faecal haem-prophyrin assay is o f considerable clinical utility, it is a quantitative index rather tha n an absolute measure when low amounts of bleeding originate from the proximal gastrointestinal tract.