Original Investigation
Pathogenesis and Treatment of Kidney Disease
Estimation of GFR in South Asians: A Study From the General Population in Pakistan

https://doi.org/10.1053/j.ajkd.2013.07.023Get rights and content

Background

South Asians are at high risk for chronic kidney disease. However, unlike those in the United States and United Kingdom, laboratories in South Asian countries do not routinely report estimated glomerular filtration rate (eGFR) when serum creatinine is measured. The objectives of the study were to: (1) evaluate the performance of existing GFR estimating equations in South Asians, and (2) modify the existing equations or develop a new equation for use in this population.

Study Design

Cross-sectional population-based study.

Setting & Participants

581 participants 40 years or older were enrolled from 10 randomly selected communities and renal clinics in Karachi.

Predictors

eGFR, age, sex, serum creatinine level.

Outcomes

Bias (the median difference between measured GFR [mGFR] and eGFR), precision (the IQR of the difference), accuracy (P30; percentage of participants with eGFR within 30% of mGFR), and the root mean squared error reported as cross-validated estimates along with bootstrapped 95% CIs based on 1,000 replications.

Results

The CKD-EPI (Chronic Kidney Disease Epidemiology Collaboration) creatinine equation performed better than the MDRD (Modification of Diet in Renal Disease) Study equation in terms of greater accuracy at P30 (76.1% [95% CI, 72.7%-79.5%] vs 68.0% [95% CI, 64.3%-71.7%]; P < 0.001) and improved precision (IQR, 22.6 [95% CI, 19.9-25.3] vs 28.6 [95% CI, 25.8-31.5] mL/min/1.73 m2; P < 0.001). However, both equations overestimated mGFR. Applying modification factors for slope and intercept to the CKD-EPI equation to create a CKD-EPI Pakistan equation (such that eGFRCKD-EPI(PK) = 0.686 × eGFRCKD-EPI1.059) in order to eliminate bias improved accuracy (P30, 81.6% [95% CI, 78.4%-84.8%]; P < 0.001) comparably to new estimating equations developed using creatinine level and additional variables.

Limitations

Lack of external validation data set and few participants with low GFR.

Conclusions

The CKD-EPI creatinine equation is more accurate and precise than the MDRD Study equation in estimating GFR in a South Asian population in Karachi. The CKD-EPI Pakistan equation further improves the performance of the CKD-EPI equation in South Asians and could be used for eGFR reporting.

Section snippets

Study Design and Participants

Participants were drawn from 2 sources. The first was a population-based sample from 10 randomly selected low- to middle-income communities in Karachi. Because the general population was expected to have few people with decreased kidney function, we enriched our sample with 40 patients with a serum creatinine level ≥ 2.0 mg/dL from the renal clinic (Fig S1, available as online supplementary material), so that 20% of our study sample would have a GFR < 60 mL/min/1.73 m2 (ie, CKD stage 3 or worse).

Participant Characteristics

Characteristics of the study population are described in Table 1. Of 581 enrolled participants, 50% were men. Median mGFR, eGFRMDRD, and creatinine-based eGFRCKD-EPI values were 91.0 (IQR, 36.7), 100.5 (IQR, 40.4), and 104.4 (IQR, 25.4) mL/min/1.73 m2, respectively. Participants with mGFR < 60 mL/min/1.73 m2 were older than those with higher mGFRs (P < 0.001) and had greater waist circumference (P = 0.02), lower lean body mass (P = 0.007), lower hemoglobin level (P < 0.001), and higher systolic blood

Discussion

The new KDIGO CKD guideline recommends using the CKD-EPI creatinine equation to report eGFR unless an alternative equation has been shown to be more accurate in the local population.21 This is the first report of the performance of existing GFR estimating equations in the general population from a South Asian country using a directly measured GFR method as a reference. Using urinary inulin clearance as the gold standard, we found that the CKD-EPI creatinine equation is significantly more

Acknowledgements

The abstracts based on this work were presented at the Joint Statistical Meetings on August 6, 2013, in Montreal, Canada; World Congress of Nephrology on June 2, 2013 in Hong Kong, and 44th Annual Renal Week on November 11, 2011, in Philadelphia, PA.

We thank all research staff for their assistance and acknowledge the cooperation of Mr Ibrahim Mustafa at the Aga Khan University Hospital for logistical assistance with the GFR clinic for research participants and Dr Lise Thibaudin for inulin

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    Because an author of this manuscript is an editor for AJKD, the peer-review and decision-making processes were handled entirely by an Associate Editor (Kunitoshi Iseki, MD) who served as Acting Editor-in-Chief. Details of the journal’s procedures for potential editor conflicts are given in the Editorial Policies section of the AJKD website.

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    Copyright © 2013 National Kidney Foundation, Inc. Published by Elsevier Inc. All rights reserved.