Topographic Diagnosis of Gastrointestinal Protein Loss by Means of Radioiodine-labelled Albumin and IgG

Abstract

A method has been worked out to determine the site of plasma protein loss in proteinlosing gastroenteropathies. It uses the ratio between faecal excretion of ¹²⁵I and ¹³¹I following simultaneous i.v. injection of ¹²⁵I-IgG and ¹³¹I-albumin. 165 cases were studied (Ménétrier's disease, 12 cases; intestinal lymphangiectasia, 19; adult coeliac disease, 6; other small-intestinal diseases, 5; chronic inflammatory bowel disease, 115 (83 of whom had Crohn's disease and 32 ulcerative colitis); and neoplastic diseases, 8 cases). Gastrointestinal macromolecular leakage was detected and semiquantitated by means of ⁵¹CrCl₃ (33 cases) or ⁵⁹Fe-iron dextran (90 cases). Faecal ⁵⁹Fe clearance was significantly (p < 0.001) correlated with the catabolic rate of albumin, which again was highly correlated with IgG catabolism (r = 0.85, p < 0.001). Faecal mass was normal in Ménétrier's disease and intestinal lymphangiectasia and elevated (>200g/day) in the other groups. Faecal radioiodide ratio (¹²⁵I/¹³¹I) was inapplicable in 26 patients with low faecal excretion of both isotopes (≤1.2% of injected dose) because of inaccurate counting rates. All cases of Ménétrier's disease fell into this group. Of the remaining 139 patients, 57 had small-intestinal lesion, and 5 1 of these had a ratio of > 1.5. Forty-three of 44 with lesion of the colon had a ratio of ≤1.5. Thirty-eight patients had lesions of both large and small intestine (radiography and/or laparotomy findings). Twenty of them were operated on less than 2 years (median, 2 months) after the study. They all had ileocolic Crohn's disease. Nine of them with ileal and total colonic involvement had a ratio of ≤ 1.5. Among the other 11 patients with involvement of ileum and less than the whole colon 9 patients had a ratio of > 1.5. We conclude that the ratio ¹²⁵I/¹³¹I in the stools after i.v. injection of ¹²⁵I-IgG and ¹³¹I-albumin is a reliable indicator of the site of abnormal protein loss, provided the faecal excretion of either ¹²⁵I or ¹³¹I, or both, exceeds 1.2% of the injected dose. In patients with ileocolic Crohn's disease the ratio indicates whether the total or only part of the colon is affected. Low faecal radioiodide excretion (≤1.2% of both isotopes) in patients with moderate and severe protein loss is strong evidence of proximal protein loss.

Key-words:

• Albumin degradation
• Crohn's disease
• IgG degradation
• intestinal lymphangiectasia
• Ménétrier's disease
• protein-losing gastroenteropathies
• ulcerative colitis