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Renal function tests
1.
2. Formation of
urine as the
waste product
Excretion of
NPN
substances
Regulation of
salt & water
balance
Regulation of
acid-base
balance
Production of
Hormones
Functions of
KIDNEY
3. Assessment of the
extent of renal
damage
Monitoring the
progression of renal
damage
Monitoring and
adjusting the dose
of renal toxic drugs
Renal Function Tests –required for……
8. Renal clearance of a substance is defined as the
volume of plasma from which the substance is
completely cleared by the kidneys per minute
9. • Endogenous creatinine and urea
• Exogenous inulin
Substances used for clearance test
Renal clearance test used to assess the rate of
glomerular filtration and renal blood flow
10. Creatinine
• Based on the rate of excretion by the kidneys
of metabolically produced creatinine
Creatinine clearance test
Creatinine
17. • Proteinuria in urine is an indicator of leaky
glomeruli
• 30-300mg/day is called microalbuminuria
• Microalbuminuria is the earliest sign of renal
damage
Small amount of protein usually less than
30mg/day, is found in urine
Cx = (UxV)/P
Cx is clearance of a substance x, Ux and Px are concentrations of the substance in urine and plasma respectively, and V the volume of urine per unit time.
In estimating clearance, concentration and volume units must be consistent. For example, if urine creatinine concentration is 70 mg/dL and volume is 2000 mL/day, urine creatinine must also be expressed in mg/mL, not mg/dL. So the total amount excreted is: 0.7 mg/mL × 2000 mL/day = 1400 mg/day.
A clearance in mL/24 hours can be converted to a clearance in mL/min by dividing the value by 1440, since 24 hours equals 1440 minutes.
Quick Formulas for the Calculation of Clearance
When calculating a 24-hour clearance in mL/min, urine creatinine excretion may be expressed in g/24 hours instead of mg/24 hours while expressing the plasma creatinine as mg/dL instead of mg/mL. The incorrect use of these units can be rectified by multiplying the final result by 1000 (for using g instead of mg) and then by 100 (for using mg/dL instead of mg/mL). A further correction requires dividing the value by 1440 in order to convert a 24-hour clearance value to a value in mL/min as follows ( Carroll, 1989 ):
(14-7) Cx = UxV (g/24 hours)/Px (mg/dL) × 100 000 × 1/1440
Since 100 000/1440 = 70:
(14-8) Cx (mL/min) = Ux (g/day) × 70/Px (mg/dL)
