Renal Function Tests : Group II tests and Group III tests

Group II tests

a.      Serum total protein, albumin, globulin and A/G ratio

b.      Quantitative determination of urinary proteins

c.      Electrophoresis of serum proteins

d.      Lipid profile ; mainly cholesterol, Triglycerides (TAG)

These tests mainly help in differentiating nephritic syndrome (glomerulonephritis) from nephrotic syndrome. These tests also help in differentiating different types of proteinuria (selective, non-selective, high molecular, low molecular weight, glomerular, tubular, overflow, etc). Electrophoretic pattern also helps to distinguish different types of proteinuria.

Group III tests

Measurement of GFR:

It is measured as clearance which means volume of plasma cleared off of the substances per unit time from glomeruli. In general proteins with molecular weight greater than albumin (66 kDa) are retained by glomerulus and are called HMW proteins. The properties of ideal marker used to assess GFR are,

1. Not be protein bound
2. Must be completely and freely filtered by glomerulus.
3. It must be solely eliminated by this route (i.e. must not be metabolized by liver)
4. Neither secreted nor absorbed in nephron
5. Produced endogenously at constant rate
6. Must be non toxic and be measured easily and accurately.

Clearance (ml/min) or GFR = (U X V)/P

Where U is urinary concentration of substance, V is rate of formation of urine (24 hr is collected and volume measured and converted to ml/min) and P is plasma concentration of substance.

Kidney size and GFR are roughly proportional to body size. It is conventional therefore to adjust 

clearance estimates to standard body surface area (BSA) of 1.73 m², according to formula devised by Du bois and Du Bois in 1916.

BSA = weight (kg) ^0.425 x height (cm) ^0.725 x 7.1 x 10^-3.