U01.21.027 Renal Clearance (Cx)

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Learning Objective:
Understand and apply the formula for renal clearance (Cx), which quantifies the volume of plasma cleared of a substance per unit time by the kidneys.

Formula:

C_x = \frac{U_x \times V}{P_x}

Explanation:

  • C_x = Clearance of substance x (mL/min)
  • U_x = Urine concentration of substance x
  • V = Urine flow rate (mL/min)
  • P_x = Plasma concentration of substance x

This equation measures how effectively the kidneys remove a substance from the plasma.
Different substances reflect different renal functions:

  • Inulin clearance → GFR (freely filtered, not reabsorbed or secreted)
  • PAH clearance → RPF (filtered and secreted; nearly 100% cleared)
  • Creatinine clearance → estimates GFR (slightly overestimates due to secretion)

Interpretation:

  • High Cx: substance is filtered and secreted
  • Low Cx: substance is reabsorbed

Example:

Given:
U_x = 100 \text{ mg/dL}
V = 1 \text{ mL/min}
P_x = 10 \text{ mg/dL}

C_x = \frac{100 \times 1}{10} = 10 \text{ mL/min}

✅ Answer: Renal Clearance = 10 mL/min

Activity:

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