Diagnostic Use
Estimated glomerular filtration rate (eGFR) is calculated using the CKD-EPI Creatinine 2009 equation, from plasma creatinine (in umol/L), age (in years, ≥18years) and gender. Overall accuracy of the equation: about 87% of the eGFR are within 30% of the measured GFR (ref 1). This equation is endorsed by the Australasian Creatinine Consensus Working Group.
Routine eGFR calculation is not offered alongside all plasma creatinine reports. However, eGFR calculation can be ordered specifically on the request form or test add by ringing 09-2760044 ext 58519.
eGFR is UNRELIABLE in the following situations:
When meat or fish is ingested during the 2 hours period preceding collection of the blood sample used for the creatinine measurement
Acute changes in renal function. eGFR is only valid in subjects in a steady state with respect to plasma creatinine
Dialysis-dependent patients
Patients with unusually high or low muscle mass. Glomerular function may be better assessed by e.g. 24 hour urine creatinine clearance test.
Creatine supplements
Children less than 18 years of age
Pregnancy
Severe liver disease
In most out-of-hospital settings, where an eGFR result is on hand and no other measure of GFR is known or readily accessible, eGFR (corrected back for the patient’s specific body size/body surface area especially if extreme body habitus) can be used to assist drug-dosing decision making. However, if critical dose adjustments is required for some narrow therapeutic index medications affected by reduced GFR, then therapeutic drug monitoring or a valid marker of drug effect should be used to individualise dosing. Direct measurement of creatinine clearance (via timed 8 hours or 24 hours urine collection) may be more appropriate – consult your team pharmacist.
eGFR and Definition of Chronic Kidney Disease
Chronic Kidney Disease (CKD) is defined as abnormalities of kidney structure or function, present for >3 months, with implications for health (ref 2). CKD involves either of the following 2 criteria:
A. Evidence of kidney damage (with or without decrease in GFR) for ≥ 3months, irrespective of underlying cause of the kidney disease:
Persisting albuminuria (>3mg/mmol creatinine ratio. First void urine preferable)
Haematuria after exclusion of urological causes
Structural abnormalities e.g. from renal imaging
Pathological abnormalities e.g. from renal biopsy
Urine sediment abnormalities
Electrolyte or other abnormalities indicative of tubular disorders
History of kidney transplantation
The first 4 criteria are described in Kidney Health NZ, BPAC and Kidney Health Australia guidelines (refs. 4-6). The KDIGO 2012 guideline (ref. 2) also included the latter 3 criteria as markers of kidney damage.
B. Decreased GFR (with or without evidence of kidney damage) for ≥ 3months:
Estimated or measured GFR ±12ml/min/1.73m2 (or outside the 39-63 ml/min/1.73m2 range) before one can be 95% confident that the change cannot be explained by biological and analytical variation alone (refs. 8,9).
“Drop in eGFR” or “Progression” is indicated by:
A fall in eGFR of ≥25% with a drop in eGFR category (by convention)
A sustained decline in GFR by >5ml/min/1.73m2 per year (preferably monitored by the same method in the same laboratory). The confidence in assessing progression increases with increasing number of plasma creatinine measurements and duration of follow up (ref. 2).
Note that some medications such as ACE inhibitor and angiotensin receptor blockers can cause a predictable fall in eGFR of up to 25%, due to changes in renal blood flow. Such a fall is not regarded as pathological if the patient then reaches and stabilized at a new baseline.
Age and eGFR
Age (>60 years) is a risk factor for CKD , but is among numerous other risk factors such as (refs. 3-6):
Māori /Pacific/Indo-Asian ethnicity
Obesity
Smoking
Diabetes
Hypertension
Cardiovascular disease history
Systemic diseases that may affect the kidney
Family history of renal disease/CKD
Age is one of the variables used to calculate eGFR, noting that eGFR does fall slowly in the general population. However, age-related decision points for eGFR are not recommended in adults (ref 10). The reason is that eGFR slowly falls with ‘healthy’ aging, with many elderly falling into the CKD stage 3a (45-59ml/min/1.73m 2 ) without evidence of active or structural kidney diseases, as defined by the criteria above . An eGFR in this range therefore does not necessarily of itself indicate pathology in the absence of one or more of the above factors (ref. 3).
Conversely, in population studies CKD stage 3a (compared with those with eGFR ≥60ml/min/1.73m 2 ) is associated with a higher cardiovascular (CVD) risk at all ages (ref10). Thus, while eGFR does fall slowly in healthy older individuals it is arguable whether it should be considered purely “physiological” (refs. 2,10).
Regardless, eGFR <45ml/min/1.73m2 (CKD3b) is pathological whether other factors are present or not, and is associated with increased risk of renal and cardiovascular complications irrespective of age, particularly if persisting albuminuria is also noted (Refs. 2,11).
Testing for CKD
Targeted testing for CKD should generally be linked to routine cardiovascular disease assessment or diabetes checks. It is recommended to match the eGFR with the degree of albuminuria and assess them against a 2 dimensional grid table (e.g. at ref 2) to evaluate risk of future deterioration of kidney function as well as cardiovascular and all cause mortality (Refs. 2-6, 9).
In a stable patient without acute symptoms, an initial eGFR of 45-59ml/min/1.73m2 should prompt review of the above other possible risk factors, and should be followed up with a repeat in 3 months, to check that it is stable. Caution should also be made in prescribing certain potentially nephrotoxic or predominantly renal cleared medications. Earlier follow up may be justified depending on clinical circumstances, e.g. if the patient has been unwell or there are other reasons to suspect acute renal injury.
For further guidance, please refer to Auckland Regional Health Pathways (Medical-Nephrology – Chronic Kidney Disease (CKD) in adults)
Online eGFR calculator is available e.g. from Kidney Health Australia, at https://kidney.org.au/health-professionals/egfr-calculator/ (last accessed 15 4 2026)