Risk of overestimation of kidney function using GFR-estimating equations in patients with low inulin clearance.
BACKGROUND
Accurate estimation of the glomerular filtration rate (GFR) is very important in clinical practice. Although renal inulin clearance (Cin) is the gold standard for measuring GFR, the procedure for Cin measurement is complicated. Use of GFR-estimating equations has been increasing recently due to their simplicity. The objectives of the present study are to analyze the correlation between Cin and other GFR-estimating parameters and to investigate their clinical usefulness and limitation.


METHODS
Seventy-two Japanese patients were enrolled in this study. Cin was measured by the continuous infusion method. Serum creatinine (s-Cr), cystatin C, uric acid (UA), and hemoglobin (Hb) were measured. The Japanese formula of estimated GFR (eGFR) was as follows: eGFR (ml/min/1.73m(2) ) = 194 × s-Cr(-1.094) × Age(-0.287) × 0.739 (if female). The endogenous creatinine clearance test was also performed.


RESULTS
Levels of Cin were highly correlated with those of endogenous creatinine clearance (Ccr) (R(2) = 0.7585) and eGFR (R(2) = 0.5659). However, patients with lower Cin showed unexpectedly elevated levels of endogenous Ccr and eGFR. Moreover, the levels of eGFR tended to be unexpectedly increased in patients with low body surface area.


CONCLUSIONS
Although GFR-estimating equations are useful for estimating GFR accurately, they pose a risk of overestimation of kidney function in patients with decreased GFRor a poor physique.
Division of Nephrology, Department of Internal Medicine, Juntendo University Faculty of Medicine, Tokyo, Japan.
Junichiro
J
Nakata
Isao
I
Ohsawa
Kisara
K
Onda
Mitsuo
M
Tanimoto
Gaku
G
Kusaba
Yukihiko
Y
Takeda
Noriyoshi
N
Kobayashi
Katsuhiko
K
Asanuma
Yuichi
Y
Tanaka
Michiko
M
Sato
Yuko
Y
Inami
Hitoshi
H
Suzuki
Hiyori
H
Suzuki
Atsumi
A
Masuda
Kanae
K
Nonaka
Yu
Y
Sasaki
Atsuko
A
Hisada
Chieko
C
Hamada
Satoshi
S
Horikoshi
Yasuhiko
Y
Tomino
D000328:Adult; D003404:Creatinine / Q000097:blood / Q000652:urine; D055316:Cystatin C / Q000097:blood; D003627:Data Interpretation, Statistical; D005260:Female; D005919:Glomerular Filtration Rate / Q000502:physiology*; D006801:Humans; D007444:Inulin / Q000097:blood* / Q000652:urine*; D007677:Kidney Function Tests / Q000592:standards*; D008297:Male; D008875:Middle Aged
C525030:CST3 protein, human; D055316:Cystatin C; D007444:Inulin; D003404:Creatinine