Which of the following formulae can be used to measure GFR?

  1. U (inulin) x V (inulin) / P (inulin)
  2. U (PAH) x V (PAH) / P (PAH)
  3. V (inulin) x P (inulin) / U (inulin)
  4. V (PAH) x P (PAH) / U (PAH)