⁵⁷Co-Cyanocobalamin in the Determination of the Glomerular Filtration Rate

Abstract

Simultaneous determination of the inulin clearance and the ⁵⁷Co-cyanocobalamin clearance was performed on 17 patients, 8 with normal and 9 with impaired renal function. Seven patients (Group I) received non-radioactive hydroxocobalamin, and 10 patients (Group II) non-radioactive cyanocobalamin, for presaturating the serum proteins. The mean clearance ratio inulin/⁵⁷Co-B₁₂ was 1.54 in Group I, while it was 1.18 in Group II. This difference is statistically significant. Furthermore, the protein-bound radioactive B₁₂ was separated from the non-protein-bound part by means of albumin-coated charcoal, in the patients of Group II. The free fraction made up an average of 92% of the total activity, and calculated on this basis, the mean clearance ratio inulin/free ⁵⁷Co-B₁₂ was 1.08. The clearance of the free ⁵⁷Co-B₁₂ was not significantly different from the clearance of inulin.

Key Words:

• Cobalt isotopes
• ⁵⁷Co-cyanocobalamin clearance
• glomerular filtration rate
• renal clearance
• vitamin B₁₂