LIST OF PROCEDURES
CKD-EPI and MDRD equations are better predictors of GFR than DTPA scan using Gates
protocol
Dr. A. V. Mulay1 DNB, MSc;
Dr. Shefali Gokhale2 DNB.
Departments of Nephrology1 and Nuclear Medicine2,
Inlaks and Budhrani Hospital, Pune.
- Accurate estimation of glomerular filtration rate (GFR) is an important part of
evaluation of kidney function.
- Renal scan using radiolabels dietnylenetriaminepentaacetic acid (99mTc-DTPA) by
Gates protocol is commonly used for estimating GFR.
- MDRD and Cockroft-Gault equations are routinely used to estimate GFR.
- CKD-EPI equation was developed recently and was shown to have better performance
compared to MDRD equation.1
Objectives
- To compare performance of serum creatinine based estimating equations and 99mTc-DTPA
scintigraphy (Gates protocol) in estimating Glomerular Filtration Rate using plasma
clearance of 99mTc-DTPA as ‘Gold Standard’.
Methods
- Prospective Cohort Study
- Measured GFR (‘Gold Standard’):
- GFR was measured by plasma clearance (GFRp) of 99mTc-DTPA using multiple sampling
at 120minute, 180minute and 240minute after injection of 99mTc-DTPA.2
- The counts were plotted on an excel sheet to obtain GFR corrected to body surface
area.
Sample plot and results of GFR by plasma clearance of 99mTc-DTPA
Methods (Contd)
- Estimated GFR:
- Cockroft Gault equation and 4-variable MDRD equation was used to estimate GFR (GFRCG
and GFRMDRD).3
- CKD-EPI equation expressed on the natural scale was used to estimate GFRCKD-EPI.1
- We also determined GFR by 99mTc-DTPA renal scan (GFRs) using GE Hawkeye-4 duel headed
gamma camera and Gates protocol. (GFRS).
- We compared GFR measured by gold standard with estimated GFR by other methods using
Pearson and Spearman correlation coefficient.
- We also determined bias and precision of estimated GFR by each method.2,3
Results
- 29 Patients with age ≥ 18Years of Age
- Male - 20; Female - 9.
- Mean Age - 48.5 (15.9) Years.
- Mean GFR – 75.9 (24.7) ml/min/1.73m2.
- Correlation of GFR was best with estimated GFR by CKD-EPI equation. (rp = 0.74,
rs = 0.75).
- CKD-EPI equation also had least bias and best precision followed by MDRD equation.
- 99mTc-DTPA scan with Gates protocol had the worst bias and precision.
Table 1 – Performance of various methods for estimating GFR
|
|
Pearson Correlation Coefficient (rs)
|
Spearman Correlation Coefficient (rs)
|
Bias
|
Precision
|
|
GFRCKD-EPI
|
0.74
|
0.75
|
0.25
|
20.8
|
|
GFRMDRD
|
0.65
|
0.74
|
0.95
|
24.4
|
|
GFRCG
|
0.53
|
0.74
|
4.1
|
28.6
|
|
GFRS
|
0.64
|
0.60
|
-22.3
|
40.8
|
Limitations
- Relatively small number of patients.
- Included patients mostly in CKD stage I / II / III.
- Not validated in children (Age < 18 years).
Conclusion
- CKD-EPI equation is the best predictor of GFR in adults with stage I – III CKD,
followed by MDRD equation.
- 99mTc-DTPA scan with Gates protocol should not be used to estimate total GFR since
it performs poorly compared to serum creatinine based estimating equations.
References
- A new equation to estimate Glomerular Filtration Rate. Ann Intern Med. 2009
May 5; 150(9): 604–612.
- Estimating glomerular filtration rate in kidney transplantation: A comparisn between
serum creatinine and cystatin C based methods. J Am Soc Nephrol 16: 3763–3770, 2005.
- Evaluation of laboratory measurements for clinical assessment of kidney disease
(K-DOQI guidelines). American Journal of Kidney Diseases, Vol 39, No 2, Suppl 1
(February), 2002: pp S76-S11.0
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