Renal Function Tests Quiz

Renal Function Tests

• Kidney function tests include serum creatinine, creatinine clearance, GFR estimation, and serum urea.

Serum Creatinine

• Ideal test for kidney function because it is constant, freely filtered, endogenous, and not reabsorbed but 10% secreted.

Creatinine Clearance (GFR)

• Formula: U x V / P
• Normal range:
  • Adults: 110 ml/min
  • Elderly: 70 ml/min
• Limitations: urine collection

Functional Units of the Kidney

• The nephron: 1,000,000 to 1,300,000 nephrons per kidney
• Kidney functions:
  • Regulation: water and electrolyte balance, acid-base balance, and arterial blood pressure
  • Excretion: metabolic waste products and foreign chemicals
  • Hormonal: secretion of erythropoietin, activation of vitamin D, and activation of angiotensinogen
  • Metabolic: gluconeogenesis

Importance of Renal Function Tests

• Many diseases affect renal function
• Destruction of complete nephron or selective impairment of glomerular or tubular functions

Measurements

• Serum creatinine (Cr)
• Creatinine clearance
• Serum urea
• Electrolytes

Creatinine Clearance

• Definition: volume of plasma cleared from the substance excreted in urine per minute
• Formula: U x V / P

GFR Estimation

• Normal range:
  • 20-40 years adults: about 110 ml/min
  • Over 80 years & females: about 70 ml/min
  • Children: related to surface area, similar to young adults

Cockcroft-Gault Formula

• Alternative method to calculate creatinine clearance using serum creatinine level, sex, and weight
• Constant (K) varies with sex:
  • Males: 1.23
  • Females: 1.04 (due to relatively lower muscle mass)