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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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