## Wednesday, 29 February 2012

### Estimated GFR (kidney function %)

To calculate kidney function there are a large number of methods and equations.
Estimated GFR (eGFR) using Modification of Diet in Renal Disease (MDRD) formula is the most widely used in the UK by the NHS.

This method estimates kidney function using four variables: serum creatinine, age, race, and gender. This equation has been validated in patients with chronic kidney disease; however it is likely to be inaccurate in healthy patients with over 60% kidney function.

Creatinine
Creatinine is a break-down product of creatine phosphate in muscle, and is usually produced at a fairly constant rate by the body (depending on muscle mass).
Creatinine is chiefly filtered out of the blood by the kidneys. If the filtering of the kidney is deficient, creatinine blood levels rise. Therefore, creatinine levels in blood are used to calculate kidney function.

The formula

186 x Serum Creatinine (in mg/DL) ^ -1.154 x Age ^ -0.203 X [1.212 if black] x [0.742 if female]

^ = to the power of

So for me today it looks like this :-

My Creatinine level is 371 micromol/L so need to divide it by 88.4 to get mg/L

186 x (371 /88.4) ^ -1.154 x 39 ^ -0.203 = 16.8%

Hospital is reporting me at 16% function so either they round down or their calculation is more complex and more accurate.

Kidney disease stages
0) Normal kidney function – above 90%
1) CKD1 – above 90% function but with evidence of kidney damage
2) CKD2 (Mild) – 60% to 89% function with evidence of kidney damage
3) CKD3 (Moderate) – 30% to 59% function
4) CKD4 (Severe) – 15% to 29% function
5) CKD5 Kidney failure - less than 15% function
Some people add "D" to patients on dialysis so CKD5 becomes CKD5D although many patients in CKD5 are not yet on dialysis.
Some people add a "T" to patients who have had a transplant regardless of stage.