ESTIMATED GLOMERULAR FILTRATION RATE (eGFR)

Definition

Estimated glomerular filtration rate (eGFR) measures the rate at which the kidneys filter wastes from the blood.¹ Impaired eGFR levels indicate that the kidneys are not working properly, which can lead to Chronic Kidney Disease (CKD).

Population

eGFR was calculated based on serum creatinine (SCr) results, which were obtained for persons aged 18 years and over, who participated in the National Aboriginal and Torres Strait Islander Health Measures Survey (NATSIHMS) and who provided a blood sample. Fasting was not required for this test.

Methodology

A blood sample was collected from participants and SCr levels were measured at the Douglass Hanly Moir (DHM) laboratory.

In order to assess kidney function the eGFR was calculated using a SCr result in addition to a number of other variables such as age and sex. As such, eGFR was calculated at DHM using the following Chronic Kidney Disease Epidemiology Collaboration (CKD-EPI) equations²:

CKD-EPI equation

For females with SCr ≤ 62 mol/L: eGFR (mL/min/1.73 m2) = 144 × (SCr in mol/L × 0.0113/0.7)2 0.329 × (0.993)age in years For females with SCr > 62 mol/L: eGFR (mL/min/1.73 m2) = 144 × (SCr in mol/L × 0.0113/0.7)2 1.209 × (0.993)age in years For males with SCr ≤ 80 mol/L: eGFR (mL/min/1.73 m2) = 141 × (SCr in mol/L × 0.0113/0.9)2 0.411 × (0.993)age in years For males with SCr > 80 mol/L: eGFR (mL/min/1.73 m2) = 141 × (SCr in mol/L × 0.0113/0.9)2 1.209 × (0.993)age in years

In the NATSIHMS, cut off reference values for normal and abnormal results were sourced from the Chronic Kidney Disease (CKD) management guidelines by Kidney Health Australia.¹ These guidelines are based on epidemiological data and publications of major clinical trials.

In the NATSIHMS, the following definitions were used for eGFR:

• Normal eGFR levels ≥ 60 mL/min/1.73 m²
• Abnormal eGFR levels < 60 mL/min/1.73 m².

Further test information about the analysis method and machine used to measure eGFR levels is available in Excel spreadsheet format in the Downloads page of this product.

Data items

The data items and related output categories for this topic are available in Excel spreadsheet format from the Downloads page of this product.

Interpretation

Points to be considered when interpreting data for this topic include the following:

• eGFR test results do not confirm a specific diagnosis without consultation with a health professional.
• There are a number of different test methods and equations to measure eGFR levels and they may produce different results. The data from this topic should therefore be used with caution when comparing eGFR results from other studies using a different test method or equation.
• Note that the CKD-EPI equations are only validated for use with isotope dilution mass spectrometry - traceable creatinine assays and coefficients for race are not included, therefore when comparing this data with other sources of data, it should be interpreted with care.²
• Research has raised questions regarding the appropriateness of eGFR formulae for the Aboriginal and Torres Strait Islander population. Creatinine-based formulae have several limitations, including the fact that they have only been validated in Caucasian and African American populations.³ Differences in body build and body composition between Aboriginal and Torres Strait Islander and non-Indigenous Australians suggest that eGFR may not be the best measurement of CKD risk for Aboriginal and Torres Strait Islander Australians.^{4, 5} Given this, estimates of CKD stages may also be underestimates, due to CKD stages being based on eGFR and Albumin Creatinine Ratio (ACR) data. Further research is needed to better understand this issue.

Comparability with other surveys

The NATSIHMS is the first ABS Aboriginal and Torres Strait Islander survey to collect biomedical information. Given it was also the first national level survey (ABS or otherwise) to collect such data for the Aboriginal and Torres Strait Islander population, no comparisons with previous surveys for this population are possible.

However, biomedical data was also collected for all Australians in the 2011-12 National Health Measures Survey (NHMS) and information about comparisons between the NHMS results and those of non-ABS surveys is available from the Comparisons with other Australian surveys section of the Biomedical Results for Chronic Diseases, 2011-12 publication.

ENDNOTES

1 Kidney Health Australia 2013, Chronic Kidney Disease (CKD) Management in General Practice. 2nd Edition 2012 <http://www.kidney.org.au/HealthProfessionals/CKDManagementinGeneralPractice/tabid/789/Default.aspx>, Last accessed 08/09/2014.
2 David W Johnson, Graham R D Jones, Timothy H Mathew, Marie J Ludlow, Matthew P Doogue, Matthew D Jose, Robyn G Langham, Paul D Lawton, Steven J McTaggart, Michael J Peake, Kevan Polkinghorne and Tim Usherwood, Australasian Creatinine Consensus Working Group 2012, Chronic kidney disease and automatic reporting of estimated glomerular filtration rate: new developments and revised recommendations, <https://www.mja.com.au/journal/2012/197/4/chronic-kidney-disease-and-automatic-reporting-estimated-glomerular-filtration>, Last accessed 08/09/2014.
3 National Institute of Health, 2014, 'Estimating GFR', National Kidney Disease Education Program, National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), National Institutes of Health (NIH), U.S. Department of Health & Human Services (HHS), <http://nkdep.nih.gov/lab-evaluation/gfr/estimating.shtml>, Last accessed 08/09/2014.
4 Maple-Brown LJ, Lawton PD, Hughes JT, Sharma SK, Jones GR, Ellis AG, Hoy W, Cass A, Macisaac RJ, Sinha AK, Thomas MA, Piers LS, Ward LC, Drabsch K, Panagiotopoulos S, McDermott R, Warr K, Cherian S, Brown A, Jerums G, O'Dea K, 2010, Study Protocol--accurate assessment of kidney function in Indigenous Australians: aims and methods of the eGFR study, <http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2836987/>, Last accessed 08/09/2014.
5 Maple-Brown LJ, Cunningham J, Hodge AM, Weeramanthri T, Dunbar T, Lawton PD, Zimmet PZ, Chadban SJ, Polkinghorne KR, Shaw JE and K O'Dea 2011, High rates of albuminuria but not of low eGFR in Urban Indigenous Australians: the DRUID Study, BMC Public Health, <http://www.biomedcentral.com/1471-2458/11/346>, Last accessed 08/09/2014.

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