Calculated creatinine clearance:

Cockcroft Gault equation:

This equation assumes female C_cr (creatinine clearance) is 15% less than males

  

  

ii.                  Estimated GFR:

 MDRD (Modification of Diet in Renal Disease) study equation. It is useful in estimating GFR in adults up to a value of 60 ml/min/1.73 m² body surface area. This is derived from 1628 middle aged patients with chronic renal insufficiency and hence called MDRD.

  

This equation should not be used for children, acute renal failure, pregnancy, oedematous states, muscle wasting disease, malnourished individuals. When the eGFR is >60 mL/min, value should be reported as >60 mL/min/1.73 m², owing to its decrease precision and accuracy at higher GFR values. A persistent reduction in eGFR to <60 mL/min is defined as CKD.

The reference value of GFR depends on the age. High GFR occur in adults but the GFR declines with age by 1 mL/min/1.73 m²/yr over the age of 40.

Urea concentration:

It also meets all the criteria except it is not produced at constant rate and depends on the rate of protein turnover, diet. There is significant passive reabsorption from nephron and this is high at high plasma concentration. Even dehydration can affect urea level. So it is not used in GFR.

Plasma β₂-microglobulin:

This is a component of MHC-I and is shed in constant rate and have low mol wt, passes freely through glomeruli. Its concentration rises during renal dysfunction. It is currently not used to measure GFR due to methodological difficulties. It is used in tumors and inflammatory disease where its production increases as it is an acute phase protein.