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Renal Function Test And Clearance Notes

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This is an extract of our Renal Function Test And Clearance document, which we sell as part of our Renal System Notes collection written by the top tier of Bristol University students.

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Lecture 5 Renal Function Test & Clearance

*

Renal function tests of urine o Visual examination
? Colour, clarity (frothy can indicate PROTEINURIA) o 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) o Osmolarity
? Ability to concentrate and dilute urine
? Normal range ~80-1,200mosm/L
? Cf extracellular fluid osmolarity ~285mosm/L o Measurement of GFR
? Equation

* GFR= Ux x V/Px o Rate of filtration=rate of excretion (no tubular transport) o GFR= Glomerular filtration rate o Px= Plasma conc. of x (mg/ml) o Ux= Urinary conc. (mg/ml) o 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 o UIN= 29mg/ml o V= 1.1 ml/min o PIN= 0.25mg/ml o 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 o Small amount involved in tubular transport into tubule o Ux (urinary conc) is a little high as creatinine is filtered o Px also a little too high (test picks up some non creatinine nitrogenous products in blood)

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