1. Renal Physiology and Function Part II Renal Function Tests
Ricki Otten MT(ASCP)SC
CLS 426 Urine & Body Fluid Analysis: Student Lab Rotation: Renal Physiology and Function

2. Renal Function Tests Tubular Reabsorption Glomerular Filtration
Renal Blood Flow
Tubular Secretion
CLS 426 Urine & Body Fluid Analysis: Student Lab Rotation: Renal Physiology and Function

3. Tubular Reabsorption Tests
Can the kidneys concentrate urine
“Concentration Tests”: control of fluid intake important in interpretation of test
Fluid deprivation
Free water clearance
CLS 426 Urine & Body Fluid Analysis: Student Lab Rotation: Renal Physiology and Function

4. Tubular Reabsorption Tests
Laboratory:
Specific gravity (number and density)
Refractometer
Reagent strip
Osmolality (number of particles in solution)
Better test
More accurate
CLS 426 Urine & Body Fluid Analysis: Student Lab Rotation: Renal Physiology and Function

5. Glomerular Filtration Tests
Assess filtering ability of glomerulus
“Clearance tests”
Measures the RATE at which kidneys can clear a ‘filterable’ substance from the blood
This substance must not be reabsorbed or secreted by the tubules
GFR = glomerular filtration rate
CLS 426 Urine & Body Fluid Analysis: Student Lab Rotation: Renal Physiology and Function

6. Glomerular Filtration Tests
Specimen requirements
Timed urine specimen: 24 hour collection
Plasma sample
Clearance calculation: UV = ml/min P
CLS 426 Urine & Body Fluid Analysis: Student Lab Rotation: Renal Physiology and Function

7. Glomerular Filtration Tests
Endogenous
Creatinine (most common)
Exogenous
Inulin (considered the ‘standard’)
CLS 426 Urine & Body Fluid Analysis: Student Lab Rotation: Renal Physiology and Function

8. Glomerular Filtration Tests
Creatinine clearance test
Endogenous substance (found in the body)
Produced at a steady rate
Dependent on muscle mass (male, female, child, adult)
Thus ‘normalized’ to body surface area using a nomogram
Children
Obese
CLS 426 Urine & Body Fluid Analysis: Student Lab Rotation: Renal Physiology and Function

9. Glomerular Filtration Tests
Calculate creatinine clearance: UV P
Urine creatinine (U) 185 mg/dl
Plasma creatinine (P) 0.9 mg/dl
Urine volume (V) ml/24 hr
Height 6’0”
Weight lb
CLS 426 Urine & Body Fluid Analysis: Student Lab Rotation: Renal Physiology and Function

10. Calculate Creatinine Clearance
CrCl = UV P
CLS 426 Urine & Body Fluid Analysis: Student Lab Rotation: Renal Physiology and Function

11. Calculate Creatinine Clearance
UV = 185 mg/dl x ml x 1 hour = =
P 0.9 mg/dl 24 hours 60 min
CrCl = 178 ml/min
CLS 426 Urine & Body Fluid Analysis: Student Lab Rotation: Renal Physiology and Function

12. Calculate Creatinine Clearance
UV = 185 mg/dl x ml x 1 hour = =
P 0.9 mg/dl 24 hours 60 min
CrCl = 178 ml/min
Is this normal for a 20 year old male?
CLS 426 Urine & Body Fluid Analysis: Student Lab Rotation: Renal Physiology and Function

13. Calculate Creatinine Clearance
UV = 185 mg/dl x ml x 1 hour = =
P 0.9 mg/dl 24 hours 60 min
CrCl = 178 ml/min
Is this normal for a 20 year old male?
No, it is increased
Correct value for body surface area
CLS 426 Urine & Body Fluid Analysis: Student Lab Rotation: Renal Physiology and Function

14. Corrected Creatinine Clearance
CrCl = 178 ml/min
Corrected CrCl =
CrCl x 1.73m2 = ml/min x 1.73
BSA
= = ml/min
CLS 426 Urine & Body Fluid Analysis: Student Lab Rotation: Renal Physiology and Function

15. Corrected Creatinine Clearance
CrCl = 178 ml/min
Corrected CrCl = 129 ml/min
Is this normal for a 20 year old male?
CLS 426 Urine & Body Fluid Analysis: Student Lab Rotation: Renal Physiology and Function

16. Corrected Creatinine Clearance
CrCl = 178 ml/min
Corrected CrCl = 129 ml/min
Is this normal for a 20 year old male? Yes
CLS 426 Urine & Body Fluid Analysis: Student Lab Rotation: Renal Physiology and Function

17. Renal Reserve Large margin of reserve in renal function
Greater than 50% of kidney function must be lost before
Clinical symptoms apparent
Biochemical abnormalities evident
Thus, not useful for screening for early renal disease
CLS 426 Urine & Body Fluid Analysis: Student Lab Rotation: Renal Physiology and Function

18. Renal Blood Flow Tubular Secretion No objectives
CLS 426 Urine & Body Fluid Analysis: Student Lab Rotation: Renal Physiology and Function

19. CLS 426 Urine & Body Fluid Analysis: Student Lab Rotation: Renal Physiology and Function