GFR Calculator(Glomerular Filtration Rate)

The kidneys are bean-shaped organs located on the dorsal side of the abdominal cavity. Each kidney is made of millions of tiny units called nephrons that help in the filtration process. When the kidneys are fully functional, they filter out waste and excess fluids that become a part of the urine the body makes each day. When there is a slight change in the function of kidneys, the wastes and fluids are not eliminated completely, which may lead to health issues. The Glomerular Filtration Rate (GFR) helps us estimate how healthy and functional the kidneys are. A low GFR indicates kidney disease and should be rectified immediately.

Age

What Is The GFR Calculator?

The glomerular filtration rate calculator is the best method to measure the level of your kidney function and determine the stage of kidney disease (1) .

Why We Should Calculate The GFR

Calculating the GFR can help in estimating the extent of damage to the kidneys. If the GFR is low, it indicates the low functioning of the kidneys and is a sign of the initial stage of kidney disease. It is also helpful in many clinical situations, such as monitoring patients with chronic kidney disease(CKD), patients with a single kidney or renal transplant recipients, evaluation of renal donors, etc. (2) .

How To Calculate GFR – GFR Calculator

The Glomerular Filtration Rate calculator gives the results of GFR based on the serum creatinine (value obtained from lab tests), age, race, and gender.

The GFR calculator uses the following three formulas:

IDMS Traceable MRD Study Equation:

GFR = 175 × (SCr)-1.154 × (age)-0.203 × (0.742 if female) × (1.212 if Black)

where SCr = serum creatinine in mg/dL

The CKD-EPI formula

Black female

If SCr

GFR = 166 × (SCr/0.7)-0.329 × 0.993age

If SCr > 0.7

GFR = 166 × (SCr/0.7)-1.209 × 0.993age

Black male

If SCr

GFR = 163 × (SCr/0.9)-0.411 × 0.993age

If SCr > 0.9

GFR = 166 × (SCr/0.9)-1.209 × 0.993age

Non-black female

If SCr

GFR = 144 × (SCr/0.7)-0.329 × 0.993age

If SCr > 0.7

GFR = 144 × (SCr/0.7)-1.209 × 0.993age

Non-black male

If SCr

GFR = 141 × (SCr/0.9)-0.411 × 0.993age

If SCr > 0.9

GFR = 141 × (SCr/0.9)-1.209 × 0.993age

The Mayo Quadratic Formula

If SCrCr

Estimated GFR for children using Schwartz formula

GFR = 0.413 × height(in cm) / SCr

For example, to calculate the eGFR of a female whose age is 35 years and the serum creatinine levels are 1.1, use the IDMS Traceable MRD study equation:

GFR = 175 × (SCr)-1.154 × (age)-0.203 × (0.742 if female) × (1.212 if Black)

where SCr = serum creatinine in mg/dL

=175x(1.1)-1.154 x (35)-0.203x(0.724)x 1.212

eGFR =68.5mL/min/1.73m2

To calculate the GFR of a 9-year-old boy whose serum creatinine is 0.8 and height is 133cm

GFR = 0.413 × height(in cm) / SCr

=0.413x 132/0.8

eGFR =68.1ml/min/1.732m2

Results Of GFR And CKD

A GFR above 60mL/min is usually considered normal for most patients and does not indicate kidney disease. If there is a significant decline in the GFR since the previous test, it could indicate kidney disease. The following table shows the results of GFR in correlation with the stages of chronic kidney disease (CKD).

STAGEGFR VALUE (mL/min)
Normal90+ or above and no proteinuria
CKD 190+ with evidence of kidney damage
CKD 2 (mild)60 to 89 with evidence of kidney damage
CKD 3 (moderate)30 to 59
CKD415 to 29
CKD 5 (Kidney failure)Less than 15

How To Compare Serum Creatinine Level To GFR

Creatinine is a waste product produced by the breakdown of the muscles and is eliminated through the kidneys. The level of creatinine in the blood is useful for the assessment of kidney function or the glomerular filtration rate (GFR). Men have a higher muscle mass and slightly higher creatinine levels compared to women and children (3) .

The normal serum creatinine range is 0.6-1.1mg/dL for females and 0.7-1.3mg/dL for males (4).An increased creatinine level causes low GFR and thus impaired kidney function.

The National Kidney Disease Education Program (NDEP) recommends a threshold of GFR (5).

GFR Chart By Age

In adults, the normal GFR is more than 90, but as the age progresses, there is a decline in GFR even without kidney disease. The chart below gives an idea of GFR based on age (1).

AGE (years)Estimated GFR
20-29116
30-39107
40-4999
50-5993
60-6985
70+75

What GFR Level Requires Dialysis?

A GFR rate of less than 15 indicates chronic kidney disease and may also result in kidney failure. Such individuals may require dialysis, which is helpful in removing wastes and excess fluid from the blood (6).

Are GFR And Creatinine Clearance The Same?

Creatinine clearance is a 24-hour urine collection used to measure the amount of creatinine excreted by the kidneys. The doctor will advise blood and urine tests to estimate creatinine clearance.

GFR is an overall measure to determine your glomerular filtration rate. Both are not the same as creatinine clearance is slightly higher in range compared to GFR and is produced by the proximal convoluted tubule.

Normal creatinine clearance is 88-128mL/min for healthy females and 97-137mL/min for healthy males (7) .

Will Drinking Water Increase My GFR?

Water is the elixir of life and helps in various biochemical pathways. It also helps to eliminate excess waste from our bodies through urine. Drinking water has little effect on increasing GFR, and if the damage to the kidney has already started, there is not much effect.

A study published in the Journal of the American Medical Association found that increasing water intake had no effect on patients with chronic kidney disease (8).

Can Dehydration Affect GFR?

Dehydration refers to excessive loss of water from the body in the form of sweat and urine.Water plays a significant role in removing the toxic load from the body. If the body is dehydrated, the load on the kidneys increases, and the elimination of toxins will be slow. Thus, due to the burden on the kidneys, the waste gets accumulated and causes a decline in GFR (9)

If the body is well hydrated, the GFR will increase in case the kidney damage has not occurred.

What Does 50 Percent Kidney Function Mean?

The kidneys are said to be healthy when they are 100% functional. But as the damage to the kidneys starts, there would be a reduction in the functional capacity.

Most people with 50 percent functional kidneys are still able to prevent their kidneys from progressing to failure or chronic kidney disease stage. This stage is also known as CKD stage 3. In this stage, there would be leakage of protein or blood in the urine as the filtration is affected.

References

1. Estimated Glomerular Filtration Rate (eGFR), National Kidney Foundation.https://www.kidney.org/atoz/content/gfr

2. Measurement of renal function in patients with chronic kidney disease, British Journal of Clinical Pharmacology, US National Library of Medicine, National Institutes of Health.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3791974/

3. Creatinine blood test, Medline Plus, US National Library of Medicine, National Institutes of Health.https://medlineplus.gov/ency/article/003475.htm

4. Creatinine (Blood), University of Rochester Medical Center.https://www.urmc.rochester.edu/encyclopedia/content.aspx?ContentTypeID=167&ContentID=creatinine_serum

5. Recommendations for improving serum creatinine measurement: a report from the Laboratory Working Group of the National Kidney Disease Education Program. Clinical Chemistry, US National Library of Medicine, National Institutes of Health.https://www.ncbi.nlm.nih.gov/pubmed/16332993

6. Chronic Renal Failure, StatPearls, US National Library of Medicine, National Institutes of Health.https://www.ncbi.nlm.nih.gov/books/NBK535404/

7. Renal function in diabetic nephropathy, World Journal of Diabetes, US National Library of Medicine, National Institutes of Health.https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3083882/

8. Drinking more water does not slow decline of kidney function for kidney disease patients, EurekAlert.https://www.eurekalert.org/pub_releases/2018-05/lhri-dmw050818.php

9. Effect Of Dehydration Produced By Water Deprivation, Diarrhea And Vomiting On Renal Function In Infants, Pediatrics, Official Journal of the American Academy of Pediatrics.https://pediatrics.aappublications.org/content/7/3/328

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