Glomerular Filtration Rate (GFR)

Your healthcare practitioner may order the GFR test if you are at a higher risk of developing kidney disease due to:

• Frequent urinary tract infections
• Diabetes
• Heart disease
• High blood pressure
• Urinary blockage
• Family history of kidney disease

GFR test may also be ordered for people who show the following symptoms of kidney disease:

• Decrease in urine quantity 
• Puffiness around eyes 
• Swelling in the face, wrists, abdomen, thighs or ankles
• Foamy, bloody or coffee-coloured urine
• Burning sensation or abnormal discharge during urination
• Change in the frequency of urination at night 
• Mid-back pain below the ribs
• High blood pressure 
• Urinating more or less often
• Feeling itchy
• Tiredness
• Loss of concentration
• Loss of appetite
• Nausea and vomiting 
• Swelling or numbness in hands and feet
• Darkened skin
• Muscle cramps

Additionally, this test is ordered periodically to monitor kidney function in people with chronic kidney disease.

You may be advised to fast overnight before this test. Avoid consuming meat a day before the test. Please inform your doctor if you are taking any prescription or over-the-counter medicines, illegal drugs, vitamins or supplements. Your doctor may ask you to temporarily stop certain drugs that may alter the test results. Medicines such as cimetidine, cephalosporin, gentamicin, cisplatin and cefoxitin can increase the creatinine level, whereas trimethoprim decreases it. However, do not stop any medicine without consulting the healthcare practitioner. Also, avoid exercising before the test. 

Your doctor or laboratory technician will draw a small blood sample from a vein in your arm and immediately send it to the laboratory for testing. 

This procedure usually takes less than three minutes. After the test, you may experience mild pain or bruising at the site of needle insertion; however, these symptoms will subside shortly after the test.

Normal results:

A normal GFR indicates that your kidneys are functioning properly. The glomerular filtration rate is reported in millilitres/minute/1.73 metre2 (mL/min/1.73 m2). 

In adults, the GFR is normally more than 90 mL/min/1.73 m2; however, it decreases with age even in the absence of kidney disease.

Based on age, the mean GFR is as follows:

Abnormal results:

Higher than normal GFR may occur in the following conditions:

• Exercise
• Pregnancy
• High cardiac output syndromes

Low GFR indicates chronic kidney disease. By estimating the GFR, doctors can determine the stage of chronic kidney disease. The following table shows the relation between the GFR and the stage of kidney disease: 

Conditions that cause decreased GFR are:

• Congestive heart failure
• Cirrhosis with ascites (liver disease with fluid accumulation in the abdomen)
• Shock
• Dehydration

Sometimes, an individual without kidney disease can show abnormal results due to:

• Obesity 
• Bodybuilding 
• Malnutrition
• Following a strict vegetarian diet
• Consuming less proteins
• Taking creatine dietary supplements

Disclaimer: All results must be clinically correlated with the patient’s complaints to make a complete and accurate diagnosis. The above information is provided from a purely educational point of view and is in no way a substitute for medical advice by a qualified doctor.