Group IV , V and VI test for renal function tests:

Group IV test

Measurement of tubular function

        i.            Detection of aminoacidurias (tubular, secretory) and glycosuria (renal)

      ii.           

Test of urinary concentrating ability by measuring specific gravity. It is used to assess state of hydration/dehydration or as an indicator of the concentrating ability of the kidneys.

Normal range for urinary SG is 1.005-1.030. Low SG can occur in diabetes insipidus and pyelonephritis and glomerulonephritis. High SG can be seen in diabetes mellitus, CHF, dehydration, liver disease.

    iii.            

The concentrating ability can also be quantified by measuring urinary osmolality. It is a measure of concentration of free particles in a solution (ionized or unionized). Osmolarity = molarity x number of particles (ions or non ions). Osmolality of >600 mOsm/kg/H₂O, is normal. In chronic progressive kidney disease this concentrating ability is diminished and in glycosuria this is increased.

     iv.             

 Diluting ability is measured by measuring urinary output after ingesting a large volume of water; SG is also measured along with it and should be normal.

       

Urinary acidification test is done by ammonia loading test. During this process NH₄Cl is administered orally and pH of the urine is measured and NH₃ determined. In renal diseases NH₃ excretion is low and pH remains acidic.

     vi.           

Renal capacity of elimination of substance is done by 15 minute PSP (phenol sulphthalein) excretion test is done. This dye is 94% excreted by tubules and only 6% by glomerular filtration. Thus the test measures primarily tubular activity. During this PSP (phenol red) is injected IV and normal kidney should excrete 30-50% within first 15 minute. Value <25% during this period indicates impaired renal function.

Group V tests

a)      Serum electrolytes (Na, K, Cl^-, HCO₃^-)

b)     Serum inorganic phosphorus, calcium

c)      Blood gases (pO₂, pCO₂) and blood pH

These tests measures the acid-base and electrolyte status

Group VI test

Test measuring renal blood flow: Substance like p-aminohippurate (PAH) is removed about 90% from plasma in a single pass through kidney.