Gastro-intestinal blood loss measured by radioactive chromium.

A new technique is described for the measurement of blood loss in the faeces of patients labelled with radioactive chromium ((51)Cr). The method is simple and is probably more accurate at low levels of faecal radioactivity than those previously described. The method will measure as little as 0.02muC of (51)Cr in whole blood in a 24-hour stool. The apparent average daily blood loss in a series of 10 normal people averaged 0.6 ml., with a range of 0.3 to 1.3 ml. Estimations of plasma and salivary radioactivity have been made in an attempt to assess the importance of contamination from eluted (51)Cr. Minor radioactivity in plasma but none in saliva was recorded. Stool contamination from such sources is thought to be insignificant. No significant correlation existed between chemical occult blood tests and isotope measurements, where there was less than 10 ml. of whole blood in a 24-hour stool.