Renal Function Tests (RFT)
Tests to assess renal functions:
A. Glomerular Function Tests
Urea clearance test
Creatinine clearance test
Inulin clearance test
B. Tubular Function Tests
Urine concentration or dilution test
Urine acidification test
C. Analysis of Blood/ Serum: Estimation of
Blood serum
Serum creatinine
Total protein
Electrolyte (Na & k+)
Urine Examination: -
Routine examination of urine volume, PH, Specific gravity, osmolality& presence
of certain abnormal constituent like glucose, protein, blood, ketone bodies etc.
also helps, of course to a limited degree, to assays kidney functioning.
Clearance Tests:
The clearance tests, measuring the GFR are most useful in assaying the renal
function.
Definition
It is defined as the volume of substance which is completely cleared by the blood
or plasma in a given unit of time by both kidneys.
It is expressed as ml/min
It is calculated by:
Where;
U∗V
C= P
U= concentration of substance in urine.
P= concentration of substance in plasma.
V= volume of urine in ml/min.
C= Clearance.
These includes:
1. Creatinine clearance Test.
2. Urea clearance Test.
1. Creatinine Clearance Test:
Creatinine is an execratory product derived from creatine
phosphate (largely present in muscles).
The excretion of creatinine is rather constant & is not
influenced by body metabolism or dietary factors.
The value of creatine clearance is closed to GFR hence its
measurement is a sensitive & good approach assess the
renal glomerular functions.
It may be defied as the volume(ml) of plasma that would be
completely cleared of creatinine per minute.
Reference value = 120 to 145 ml/min
Diagnostic importance: - A decrease in creatinine clearance
value (<75% normal) Serves as sensitivity indicator of a
decreased GFR, due to renal damage. This test is useful for
of any early detection of impairment in kidney function,
often before the clinical manifestations are seen.
2.Urea clearance Test:
Urea is the end product of protein metabolism.
After being filtered by the glomeruli, it is a
partially reabsorbed by the renal tubules.
Hence, urea clearance less than CFR and
further, it is influenced by the protein content
of diet. For this reason, urea clearance is not a
sensitive as a creatinine clearance for assessing
renal function.
It may be defined as the volume(ml) of plasma
that would be completely cleared of urea per
time.
Reference value = 75 ml/min
Diagnostic importance: - A urea clearance value below 75 %
of the normal viewed seriously, since it is an indicator of
renal damage. Blood Urea level such as found to increase
only when the clearance falls below 50% normal.
