best practice 6, June Renal Update
GFR is Glomerular Filtration Rate and it is a key indicator of renal function. eGFR is derived entity based on a patient's serum creatinine level, age, sex and race. eGFR if possible although one can be calculated using an eGFR calculator. Serum creatinine itself is not a good marker of renal function and moderate renal Creatinine clearance is a surrogate marker of the GFR but several variables can affect the An online and downloadable eGFR calculator is available from. The creatinine clearance is a widely used test to estimate the 10 to 20 percent of urinary creatinine in patients with a normal GFR and a.
For this reason, other equations have been developed to aid clinicians in estimating renal function for the purposes of drug dosing.
Creatinine Clearance Calculator
The two most common equations for estimating unstable renal function are the Jelliffe 8 and Chiou 9 methods. Generally speaking, these equations are developed using a one-compartment pharmacokinetic estimation model, and are less accurate when renal function is improving rather than worsening. For the purposes of drug dosing or estimating GFR in patients with body size that is very different than average, GFR can be non-normalized using the following equation: Historically, the Cockcroft-Gault and Jelliffe equations used an arbitrary value of 0.
Fortunately, newer data have shown that this correction factor is actually relatively accurate, with an "optimal" correction factor between 0. Serum creatinine production is approximated based on lean body weight because muscle tissue not fat is responsible for creatine production.
Furthermore, a change in total body mass does not increase the size of the kidney or GFR proportionally. Equations that do not correct or adjust for obesity risk overestimation of true renal function. In one of the largest study on the topic to date of nearly overweight and obese patients, the following conclusions can be drawn: In the process of conversion, however, the non-normalized value will also overestimate GFR in obese patients.
This equation was not scientifically derived or validated, 15 but is extensively used in medicine. A newer equation, called LBW 19 may be a more promising estimation of lean body weight and has been derived and validated with actual patient data.
Most laboratories in New Zealand now automatically report eGFR whenever a serum creatinine is requested. This allows the practitioner to assess kidney function without having to estimate creatinine clearance using the Cockcroft-Gault equation.
- Renal function
- Creatinine Clearance and Estimated Glomerular Filtration Rate--When are they Interchangeable.
Provision of the eGFR allows an initial screen for chronic kidney disease and the possibility of early detection. Ethnicity factors have not yet been calculated for other ethnic groups.
This gives a convenient method of consistent reporting of eGFR which can be related to renal function and stages of CKD.
An online and downloadable eGFR calculator is available from http: The indications for referral to a nephrologist are: This is especially important in populations at high risk of renal disease in which the MDRD equation has not been validated e. These are; Acute changes in kidney function e. Paraplegia, amputees and those with very high muscle mass.
Creatinine Clearance and Estimated Glomerular Filtration Rate--When are they Interchangeable.
Age less than 18 years. The use of eGFR has not been validated for the adjustment of drug dosages. The Cockcroft-Gault equation is still recommended for this. This means there could be significant differences in the two values in people at extremes of body size. Drug datasheets advise dose adjustments according to values of creatinine clearance.