Creatinine and eGFR

Creatinine is one of the most commonly ordered blood tests. It is used to assess your kidney function.

If you are experiencing new-onset symptoms (symptoms lasting less than 3 months) or are unwell, we recommend seeking follow-up at an urgent care centre or walk-in clinic for assessment by a physician as your symptoms may be part of an acute illness that requires immediate intervention by a physician and may represent a life-threatening disease.

Why is assessing kidney function important?

Chronic Kidney Disease (CKD) is becoming more prevalent with higher rates of obesity and diabetes and leads to poor health outcomes. Testing your kidney function allows doctors to determine if there is an underlying disease causing damage to your kidneys.

What is creatinine?

The body produces creatinine as a breakdown of creatine phosphate which plays an important role in muscle metabolism. When creatinine is produced through normal muscle use, it is released into the bloodstream and filtered through your kidneys and excreted into your urine.

What is eGFR?

The estimated glomerular filtration rate (eGFR) is the measure of your kidney function. It is calculated using the creatinine levels in your blood in combination with your age and sex since these affect your kidney function (GFR gradually drops as we get older).

What is a urine ACR test?

Urine ACR is a measurement of kidney damage. It is called urine albumin to creatinine ratio. The liver produces an important protein, albumin, which is carried in the bloodstream. Normal kidney function prevents leakage of albumin into the urine. When the kidney is damaged, small amounts of albumin leak into the urine. High amounts of albumin compared to creatinine in urine indicate kidney disease.

What is normal kidney function?

Normal kidney function is eGFR > 60 and ACR < 3 mg/mmol.

What is abnormal kidney function?

Abnormal kidney function is when your eGFR is < 60 or your urine ACR > 3 mg/mmol.

What are the risk factors for kidney disease?

• Hypertension

• Diabetes Mellitus

• Age 60-75 with cardiovascular disease

• First Nations, Inuit or Metis background

• 1st Degree Relative (Father, Mother, Brother, Sister) with Chronic Kidney Disease (CKD)

• Auto-immune disease (i.e. lupus, Crohn’s disease, diabetes mellitus)

• Smoking

• On Medication with kidney toxicity (i.e. NSAIDS - daily ibuprofen/advil, naproxen/aleve, celebrex, etc)

What happens if I have reduced eGFR?

When you are noted to have a reduced eGFR, Canadian Guidelines recommend a repeat eGFR test with a urine ACR (albumin-to-creatinine) ratio 3 months after your initial test. If you have a single measurement of an eGFR < 60, you do not have kidney disease. If you suddenly have had a drop in your eGFR, doctors repeat the test sooner than 3 months to ensure there isn’t a rapid decline in your kidney function that warrants earlier investigation.

What should I do if I have a reduced eGFR?

We recommend assessment at a local walk-in clinic to evaluate your blood pressure and complete a physical examination.

References

[1] Johnson CA, Levey AS, Coresh J, Levin A, Lau J, Eknoyan G. Clinical practice guidelines for chronic kidney disease in adults: Part I. Definition, disease stages, evaluation, treatment, and risk factors. Am Fam Physician. 2004 Sep 1;70(5):869-76. PMID: 15368726.

[2] Guidelines for the management of chronic kidney disease

Adeera Levin, Brenda Hemmelgarn, Bruce Culleton, Sheldon Tobe, Philip McFarlane, Marcel Ruzicka, Kevin Burns, Braden Manns, Colin White, Francoise Madore, Louise Moist, Scott Klarenbach, Brendan Barrett, Robert Foley, Kailash Jindal, Peter Senior, Neesh Pannu, Sabin Shurraw, Ayub Akbari, Adam Cohn, Martina Reslerova, Vinay Deved, David Mendelssohn, Gihad Nesrallah, Joanne Kappel, Marcello Tonelli

CMAJ Nov 2008, 179 (11) 1154-1162; DOI: 10.1503/cmaj.080351

[3] Ontario Renal Network - Kidneywise Toolkit

[4] Chronic Kidney Disease - Identification, Evaluation and Management of Adult Patients [https://www2.gov.bc.ca/gov/content/health/practitioner-professional-resources/bc-guidelines/chronic-kidney-disease#15]