What is Glomerular Filtration Rate (GFR)

     GFR (glomerular filtration rate) is the optimal way to measure kidney function and determine a person's stage of kidney disease. The level of GFR and its magnitude of change over time are vital to :
· the detection of kidney disease
· understanding its severity
· making decisions about diagnosis, prognosis and treatment
How is GFR measured ?
     GFR is measured using plasma or urinary clearance of an exogenous filtration marker. However, this is a complex procedure and generally not routinely performed. Therefore, GFR is usually estimated from the person's serum creatinine level, in combination with demographic factor such as age, race, and gender using various formulas.
What does GFR indicate ?
     GFR is equal to the total of the filtration rates of the functioning nephrons in the kidney. In most healthy people, the normal GFR is 90 mL/min/1.73m2 or higher.
· a result of 60-89 mL/min/1.73m2 without kidney damage may be normal in some people such as the elderly or infants (if, for example, there are no other findings indicative of kidney disease, such as protein in the urine).
· a result of 60-89 mL/min/1.73m2 for => 3 months, along with kidney damage (such as persistent protein in the urine), means the person has early kidney disease.
· When GFR is < 60 for => 3 months, chronic kidney disease (CKD) is present.
Why use GFR as a measure of kidney function ?
    

Normal GFR varies according to age, sex, and body size; in young adults it is approximately 120-130 mL/min/1.73m2 and declines normally with age. However, a decrease in GFR may also be a marker of kidney disease and precedes the onset of kidney failure; therefore a persistently reduced GFR is a specific diagnostic criterion for chronic kidney disease. Below 60 mL/min/1.73sq.m, the prevalence of complications of CKD increases, as does the risk of cardiovascular disease (CVD)
Whet does "Traceable to IDMS" mean ?
· all laboratories should now be using a creatinine method that has been standardized or traceable to isotope dilution mass spectrometry (IDMS). The way creatinine levels are calibrated affects the GFR estimating equation slightly.
· to properly estimate GFR, the serum creatinine must be measured accurately. When a laboratory calibrates their method to the single standardized serum creatinine using reference materials traceable to the primary reference material at the National Institute of Standards, we say that value is traceable to IDMS because the test is based on isotope dilution mass spectrometry (IDMS).
· with the exception of the Cockcroft-Gault formula, all other calculators in this Smartphone application are designed for use with standardized creatinine values that are traceable to IDMS. Also, only standardized cystatin C values are used.
· your laboratory can confirm whether or not it uses standardized creatinine values that are traceable to IDMS. It can also confirm whether it uses cystatin C values that are standardized.