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Medicine Notes Renal System Notes

Renal Function Test And Clearance Notes

Updated Renal Function Test And Clearance Notes

Renal System Notes

Renal System

Approximately 31 pages

These notes helped me achieve a mark of 78% in my renal system exam, which is the equivalent of a 1st. The notes are based on a series of lectures on the subject. This is a very good, thorough and in depth review of the nervous system. They are very clearly laid out and easy to follow. They cut out unnecessary information on the topic, making the notes very concise, and fast to get through. Anyone studying medicine, or any other subject requiring knowledge of the renal system (e.g. physiology or ...

The following is a more accessible plain text extract of the PDF sample above, taken from our Renal System Notes. Due to the challenges of extracting text from PDFs, it will have odd formatting:

Lecture 5

Renal Function Test & Clearance

  • Renal function tests of urine

    • Visual examination

      • Colour, clarity (frothy can indicate PROTEINURIA)

    • Labstix analysis (normal)

      • Protein (trace/none)

      • Blood (none)

      • Free haemoglobin (none)

      • Glucose (none)

      • pH (variable- normal range ~4.5-8.5 cf plasma pH 7.4)

    • Osmolarity

      • Ability to concentrate and dilute urine

      • Normal range ~80-1,200mosm/L

      • Cf extracellular fluid osmolarity ~285mosm/L

    • Measurement of GFR

      • Equation

        • GFR= Ux x V/Px

          • Rate of filtration=rate of excretion (no tubular transport)

          • GFR= Glomerular filtration rate

          • Px= Plasma conc. of x (mg/ml)

          • Ux= Urinary conc. (mg/ml)

          • V= Urine output (ml/min)

      • Inulin clearance

        • Not endogenous, not metabolised/stored by kidney, not change GFR

        • Undergoes no tubular transport and is freely filtered

        • Accurate but not convenient

        • Example

          • UIN= 29mg/ml

          • V= 1.1 ml/min

          • PIN= 0.25mg/ml

          • GFR= 19 x 1.1/ 0.25= 129ml/min=184L/day

      • Creatinine (PREFERRED CHOICE OF TEST)

        • Endogenous (require no infusion, non-toxic CONVENIENT)

        • Freely filtered, not metabolised/stored by kidney, not change GFR

        • Plasma conc. does not vary with dietary intake (cf urea) or hydration (cf urea) so, in with normal renal function, serum creatinine stable

        • Creatinine clearance (CC) measured simply- patient takes 24hr urine, and blood sample take at any time in collection period

        • Not as accurate as inulin

          • Small amount involved in tubular transport into tubule

          • Ux (urinary conc) is a little high as creatinine is filtered

          • Px also a little too high (test picks up some non creatinine nitrogenous products in blood)

          • BUT two changes cancel each other out enough, so accurate

      • Serum creatinine

        • Any increase reflects impaired glomerular filtration

        • Less accurate

          • Can’t estimate GFR in early part of curve, only late RD

          • Good for rate of deterioration in late renal disease

          • CONVENIENT

        • Decreased GFR= inreased serum creatinine

          • Equivalent to number of functional nephrons

          • Donate kidney, GFR falls by half, serum creatinine still low

      • Blood urea level

        • Not accurate for renal disease

        • Other reasons for high results (e.g. high protein meal, dehydration)

      • Cr51 EDTA Elimination

        • Rate at which radioisotope is cleared from blood

        • Inject then test to see fall in levels in blood over period of time

        • BUT risk of injecting radioisotopes and expensive...

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