Possibilities of evaluation of changes of glomerular filtration rate estimated on the basis of predicting formulas

Czech version

Authors: O. Schück ¹; M. Horáčková ¹; V. Teplan ²; M. Štollová ²
Authors‘ workplace: Interní klinika 2. lékařské fakulty UK a FN Motol Praha, přednosta prof. MUDr. Milan Kvapil, CSc. ¹; Klinika nefrologie transplantačního centra IKEM Praha, přednosta prof. MUDr. Vladimír Teplan, DrSc. ²
Published in: Vnitř Lék 2008; 54(4): 346-351
Category: Original Contributions

Overview

Introduction:
Estimation of changes of glomerular filtration rate based on accurate measurement (GFR) and that based on predicting formulas (eGFR) could differ significantly. In this study we have tried to analyse the relationship between (eGFR)t₂/ /(eGFR)t₁ and (GFR)t₂ / (GFR)t₁ (where t₁ and t₂ denote the time at the beginning and the end of the follow-up interval).

Methods:
Renal clearance of inulin (C_in) was repeatedly examined in 32 patients suffering from chronic renal impairment (S_Cr = 231 ± 70 μmol/l). Estimated GFR (eGFR) was calculated on the basis of Modification of Diet in Renal Disease (MDRD) and Cockcroft-Gault (CG) equations.

Results:
A significant relationship between (MDRD)t₂ / (MDRD)t₁ and (C_in)t₂/(C_in)t₁ (r = 0.544, p = 0.0028, R₂ = 0.295) as well as between (CG)t₂ / (CG)t₁ and (C_in)t₂ / (CG)t₁ (r = 0.556, p = 0.0026, R₂ = 0.309) was found. Average difference between (MDRD)t₂ / (MDRD)t₁ – (C_in)t₂ / (C_in)t₁ was 0.017 ± 0.17 and that of (CG)t₂ / (CG)t₁ – (C_in)t₂ / (C_in)t₁ was 0.024 ± 0,18. Within ± 0.20 of the difference (eGFR)t₂ / (eGFR)t₁ – (C_in)t₂ / (C_in)t₁ 59 % values were found and within ± 0.30 of this difference 75 % values were recorded. Highly significant relationship was found between (MDRD)t₂ / (MDRD)t₁ and (CG)t₂ / (CG)t₁ (r = 0.991; p = 0.0001; R₂ = 0.983).

Conclusion:
Considering these preliminary findings, predicting formulas are not sensitive sufficiently to by able to detect GFR changes lower than 30 % of initial value.

Key words:
formulas predicting GFR – evaluation of GFR changes – MDRD – Cockcroft-Gault equation

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