Kidney GFR question?

Question

Does anyone know the formula for calculation my GFR. I know That my dialysis unit Davita has a website called Davita.com and I can get on there and they have a built in GFR calculater but it only uses three factors. Age, race and creatinin level to calculate the GFR. This helps but I know that it is far from accurate. I have seen the formula before and there are seven or more factors needed. I have a usual GFR of 16% to 18 % GFR every month using the Davita calculater and I have to goto dialysis 2 times a week. I have been told that if I drop down under 15% that I will have to go three times a week. Lord knows that I do not want that. Believe it or not, but none of the Techs at the unit know the correct formula. I have had a docter do it for me before and when using the correct formula my GFR is 3 or 4 points higher. If you know the what I am talking about please give me the formula, and explain any hard points that I may need to know when calculatiog. Thank You

Answer 1

The new equation that uses only the age, race, gender and creatinine is actually much MORE accurate than the old equation you are thinking about.

The new equation is called the MDRD Equation and it has made it much easier to figure out Creatinine Clearance (which is similar to, and used as a proxy for GFR.)

The old equation that you are thinking of is called the Cockcroft-Gault Equation and is not really used clinically now that we have the MDRD. However, if you really want to use it, it is:

Cockcroft-Gault Equation: (140-age)*wt/(Cr*72)

Then for females multiply by 0.85 (For males do not.) The wt is in KG.

Both the Cockcroft-Gault formula and the Modification of Diet in Renal Disease (MDRD) equation are imperfect for diagnosis and risk stratification of renal failure in patients with diabetes, but the MDRD is more accurate, according to the results of a study published in the April issue of Diabetes Care.

By the way, although the MDRD looks like it uses less information, it's a much more complex equation:

GFR (mL/min/1.73 m2) = 175 x (Scr)-1.154 x (Age)-0.203 x (0.742 if female) x (1.210 if African American) (conventional units)

The equation does not require weight because the results are reported normalized to 1.73 m2 body surface area, which is an accepted average adult surface area

Hope this helps.

Answer 2

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Answer 3

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Answer 4

The usual formula doctors use is called the Cockcroft-Gault equation.

GFR = ((140 - Age) x Weight) / (72 x Creatinine)

and if you are female you multiply the whole lot by 0.85

ie. GFR = (0.85 x (140-Age) x Weight) / (72 x Creatinine)

Age in years
Weight is your mass (in kilograms)
Creatinine is your plasma creatinine (in mg/dL)

I do the 72 x Creatinine first and put that into memory storage in the calculator, then do the top bit and divide by the memory storage.

Or you could do the top bit, divide by 72 and then divide by your creatinine

Answer 5

GFR is dependent on net filtration pressure (NFP). the components include glomerular hydrostatic pressure, which is the chief force pushing water and solutes out of the blood and across the filtration membrane. colloid and capsular hydrostatic pressures opposes water and solutes across the filtration membrane. if there is increased capsular pressure, NFP is going to decrease, and also decrease GFR. NFP=hydrostatic glomerular P -(osmotic P + Hydrostatic capsular P)

Answer 6

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