Week 2- Assessment of renal function & drug handling in renal disease+ classification Flashcards
what is the main function of the kidney?
- its an Excretory organ
- but also has a metabolic and endocrine function
what can occur if there is a failure in the excretory function of the kidney?
accumulation of drugs + toxicity in renal failure
what needs to happen if the patient has renal failure?
– assess degree of renal impairment
– make adjustments
– change to safer drug
– avoid nephrotoxics
what tests are done to asses renal function? tests on the plasma?
– Creatinine
– Urea
– eGFR
what tests are done to asses renal function? tests on the urine?
– Albumin:creatinine ratio (ACR) – Osmolality – Specific gravity – Proteinuria/ Microalbuminuria – Haematuria – Mid stream urine
what is creatinine?
• By product of protein metabolism, freely filtered by the kidneys
- if there is a kidney problem creatinine levels will rise as its not being cleared
- GFR ≈ Cr Cl
what is the best way to measure creatinine clearance?
-24hrs urine collection
Cr Cl [ml/min] = Urine Cr [mol/l] x Volume [ml] /
plasma Cr [mol/l] x Time
what are some limitations of urine collection for creatinine clearance?
- Accuracy of urine collection (might forget by patient)
* Time delay in getting results by to the lab
what other method is done to calculate creatinine clearance? equation = cg
Cockcroft & Gault Equation:
Cr Cl [ml/min] =
[140-age] x IBW x F /
Plasma Cr [mol/l]
[F = 1.23 males & 1.04 females]
what are the limitations for Cockcroft & Gault Equation?
– Assumes average population data
– Unsuitable for children (separate calculation) &
pregnancy
– Renal function must be stablely off
what is the normal creatinine clearance?
Traditionally, assuming “normal” CrCl = 120ml/min
and “normal” Cr = 55-125 µmol/l
what is another way to calculate renal impairment?
eGFR THROUGH BLOOD SAMPLE
what 4 variables are used to calculate eGFR?
serum Cr, age, sex, ethnic origin
what are some limitations of eGFR?
(children, ARF, pregnancy, oedema etc)
how many stages is there for renal impairment when using eGFR?
5
what are the different stages of renal impairment for eGFR?
- Stage 1 (G1) >90 Normal GFR
- Stage 2 (G2) 60-89 Mild impairment
- Stage 3A (G3a) 45-59
- Stage 3B (G3b) 30-44 Moderate impairment
- Stage 4 (G4) 15-29 Severe impairment
- Stage 5 (G5) <15 Established/End stage
how do you improve accuracy and find out someone’s absolute GFR ? equation
GFR absolute =
eGFR x individual BSA /
1.73
what other blood test is used to work out an individual renal impairment?
urea