Dr. Navdeep Tangri has developed a new website dedicated to explaining the Kidney Failure Risk Equation and the site also provides an online calculator. Learn more here: www.kidneyfailurerisk.com. Please note, this website/tool is not run by Manitoba Renal Program.
How should estimated glomerular filtration rate (eGFR) be used?
Measurement of renal function is an essential element of patient care because it may identify kidney disease, evaluate effectiveness of therapies and/or allow for drug adjustments to prevent toxicity.
eGFR reporting using the MDRD equation implements 3 variables (age, gender and serum creatinine) in a calculation requiring utilization of a standardized serum creatinine measurement. It has only been validated for GFR <60 ml/min/1.73m2, therefore only valid for use in individuals with CKD Stages 3 through 5. This replaces the 24 hr urine collections to assess GFR. Please also read about eGFR caveats.
Manitoba labs will report eGFR:
- If a patient is 18 years of age or older
- With all serum creatinine results for non-hospitalized patients
- Only if specifically ordered for hospitalized and ER patients
a. – eGFR < 60 ml/min/1.73m2
eGFR derived by the MDRD equation has become the standard to assess kidney function in adult outpatients with stable CKD stage 3 or worse i.e. <60 ml/min/1.73m2.
Manitoba Renal Program Recommendations:
- If eGFR is reported as < 60 ml/min/1.73m2, it should be repeated to ensure not declining rapidly, and then after 3 months to determine if persistent and hence chronic. This should also be accompanied by a urinalysis and estimation of protein excretion rate.
- Routine urinalysis and an estimate of protein excretion rate should be done to help guide diagnosis, management, and predict risk of progression.
- eGFR should be used with caution in elderly individuals, and those with extreme body composition (i.e. amputations, very obese or lean) and pregnancy. eGFR may underestimate the true GFR with any of these variables.
- eGFR should not be used in patients with acute kidney injury.
- Nephrology referral should be considered for eGFR persistently < 30 ml/min/1.73m2 (CKD stage 4) and as noted in the MRP Kidney Disease Referral Pathway.
b. – eGFR > 60 ml/min/1.73m2
Approach to CKD patient management is dependent upon CKD stage, which requires an estimation of GFR rather than a precise measurement.
Patients are deemed to have CKD if there are abnormalities of kidney imaging, urinalysis, or function (eGFR < 60 ml/min/1.73m2) for greater than 3 months.
eGFR > 60 ml/min/1.73 m2 does not exclude CKD, which may be identified with evidence of other abnormalities such as proteinuria, hematuria or abnormal renal imaging.
If eGFR is found to be < 60 ml/min/1.73m2, and/or other renal investigations reveal abnormalities clinicians should refer to the MRP Kidney Disease Referral Pathway.
eGFR only provides information about the degree but not the cause of kidney impairment; further assessment of urinary sediment, protein excretion rate, and imaging, is required. Determining whether a patient has CKD should not be based on eGFR in isolation.
Interpreting eGFR < 60 ml/min/1.73m2 in those >70 years old should be done cautiously. Further assessment of urine and imaging is often necessary.
eGFR as a measure of kidney function may not be valid in the following:
- Individuals with GFR > 60 ml/min/1.73m2
- Individuals >70 years of age,
- Extremes of body mass (i.e. muscle wasting, morbid obesity)
- Vegetarian diets
- Individuals taking creatine supplements
- Individuals on drugs that inhibit the tubular secretion of creatinine (i.e. trimethoprim (Bactrim, Septra, fibric acid derivatives other than gemfibrozil))
eGFR may overestimate GFR in Asians, and has not been validated in Canadian aboriginal patients. Therefore in those situations, the eGFR when reported should be interpreted cautiously and could be supplemented with a 24 hour collection.
Creatinine clearance (Cockroft Gault) or MDRD eGFR may be used for drug dosing in adult patients with stable renal function. If a patient is to receive a more toxic renally excreted drug then it may be desirable to calculate both MDRD eGFR and Cockroft Gault creatinine clearance to assist in determining the initial dose.