Measurement of Glomerular Filtration Rate by Free Vitamin B₁₂ Clearance

Abstract

We determined the vitamin B₁₂ clearance using an ultrafiltration technique and assessed whether the clearance of this vitamin B₁₂ Could be used to estimate the glomerular filtration rate (GFR). Fourteen subjects (5 had renal disease, 7 had diabetes mellitus, one had liver cirrhosis and one had cholelithiasis) divided into two groups were studied (group 1, 5 patients without vitamin B₁₂ preloading; group 2, 9 patients with vitamin B₁₂ preloading). Vitamin B₁₂ clearance was significantly correlated with inulin clearance (r = 0.81, p < 0.001) in group 1; group 2 showed an even better correlation (r = 0.94, p < 0.001) with the presaturated vitamin B₁₂ binding protein. In group 2, the mean inulin and vitamin B₁₂ clearance values did not differ significantly (40.3 ± 13.6 vs 48.2 ± 17.2 ml/min), but there was a significant difference between mean inulin and creatinine clearance (40.3 ± 13.6 vs 64.9 ± 19.9 ml/min, p < 0.05). In conclusion, vitamin B₁₂ clearance appears to be a more reliable method of estimating GFR than creatinine clearance.
(Internal Medicine 32: 194-196, 1993)