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Renal Physiology and Function Part II Renal Function Tests

Renal Physiology and Function Part II Renal Function Tests. Ricki Otten MT(ASCP)SC uotten@unmc.edu. Renal Function Tests. Tubular Reabsorption Glomerular Filtration Renal Blood Flow Tubular Secretion. Tubular Reabsorption Tests. Can the kidneys concentrate urine

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Renal Physiology and Function Part II Renal Function Tests

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  1. Renal Physiology and Function Part IIRenal Function Tests Ricki Otten MT(ASCP)SC uotten@unmc.edu

  2. Renal Function Tests • Tubular Reabsorption • Glomerular Filtration • Renal Blood Flow • Tubular Secretion

  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

  4. Tubular Reabsorption Tests • Laboratory: • Specific gravity (number and density) • Refractometer • Reagent strip • Osmolality (number of particles in solution) • Better test • More accurate

  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

  6. Glomerular Filtration Tests • Specimen requirements • Timed urine specimen: 24 hour collection • Plasma sample • Clearance calculation: UV = ml/min P

  7. Glomerular Filtration Tests • Endogenous • Creatinine (most common) • Exogenous • Inulin (considered the ‘standard’)

  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

  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) 1250 ml/24 hr Height 6’0” Weight 260 lb

  10. Calculate Creatinine Clearance CrCl = UV P

  11. Calculate Creatinine Clearance UV = 185 mg/dl x 1250 ml x 1 hour = 178.4 = P 0.9 mg/dl 24 hours 60 min CrCl = 178 ml/min

  12. Calculate Creatinine Clearance UV = 185 mg/dl x 1250 ml x 1 hour = 178.4 = P 0.9 mg/dl 24 hours 60 min CrCl = 178 ml/min Is this normal for a 20 year old male?

  13. Calculate Creatinine Clearance UV = 185 mg/dl x 1250 ml x 1 hour = 178.4 = 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

  14. Corrected Creatinine Clearance CrCl = 178 ml/min Corrected CrCl = CrCl x 1.73m2 = 178 ml/min x 1.73 BSA 2.39 = 128.8 = 129 ml/min

  15. Corrected Creatinine Clearance CrCl = 178 ml/min Corrected CrCl = 129 ml/min Is this normal for a 20 year old male?

  16. Corrected Creatinine Clearance CrCl = 178 ml/min Corrected CrCl = 129 ml/min Is this normal for a 20 year old male? Yes

  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

  18. Renal Blood Flow • Tubular Secretion No objectives

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