Updated: 2/13/2019

Renal Clearance

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Introduction
  • Renal clearance 
    • describes the amount (volume) of plasma that is completely cleared by the kidneys per unit time
      • in other words it reflects the excretion of a substance (e.g., medications)
      • this depends on
        • glomerular filtration
        • tubular reabsorption and secretion
      • clearance decreases gradually with age but may have acute changes due to pathology    
    • equation
      • C(x) = (UxV) / P
        • C(x) = clearance of substance X (mL/min)
        • Ux = urine concentration of substance X (mg/mL)
        • V = urine flow rate (mL/min)
        • Px = plasma concentration of substance X (mg/mL)
  • Clearance ratios
    • C(inulin)
      • C(inulin) = GFR
      • inulin is freely filtered across glomerular capillaries
        • it is neither reabsorbed or secreted
          • amount of inulin filtered equals amount of inulin excreted
      • inulin is a reference substance called a glomerular marker
    • C(x) / C(inulin) > 1.0
      • C(x) > GFR
      • interpretation
        • there is a net secretion of substance X
          • e.g., para-aminohippuric acid
            • can be used to determine renal plasma flow
    • C(x) / C(inulin) < 1.0
      • C(x) < GFR
      • interpretation
        • there is a net reabsorption of subtance X
          • e.g., glucose
 
 

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(M1.RL.17.4695) A 45-year-old gentleman with a history of poorly controlled diabetes mellitus is referred to a nephrologist for evaluation of the possibility of early stage kidney failure. Upon evaluation, the nephrologist decides to assess the patient's renal plasma flow by performing a laboratory test. Which of the following substances would be the best for estimating this value? Tested Concept

QID: 107948
1

Creatinine

21%

(60/286)

2

Inulin

23%

(67/286)

3

Glucose

0%

(1/286)

4

Para-aminohippurate (PAH)

50%

(144/286)

5

Urea

3%

(8/286)

M 1 B

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