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what are 2 blood tests of renal function?
where does urea come from?
made in liver from amino acid break down
what does excretion of urea depend on?
urinary flow - hence if dehydrated serum urea goes up as less urine flow
can urea diffuse through dialysis membrane?
what factors cause plasma urea to go up?
- protein meal - eg GI bleed or steak
- impaired GFR
- catabolic state
what factors reduce plasma urea?
- low protein diet
- liver disease - not making urea
- SIADH (dilution)
how is creatinine made? from what?
- product of creatine phosphate turnover in muscle
- small amount from diet
how is creatinine excreted?
- cleared through glomerulus
- some actively secreted across renal tubule
what increases serum creatinine?
- reduced GFR
- increased muscle mass
- acute muscle damage
- protein meal
- ketones create ARTEFACTUAL rise in Cr due to interference in analysis
what decreases serum creatinine?
- small muscle mass
- xs bilirubin
how do you calculate creatinine clearance?
- urine concentration of creatinine x volume of urine
- divided by
- plasma concentration of creatinine x time period collected in mins
what formula is used to calculate eGFR and what 4 variables does this include?
- MDRD formula (modification of diet in renal disease)
- age, sex, serum creatinine, ethnicity
what is the aim of eGFR and why is this important?
- to pick up EARLY CKD
- as it is a risk factor for CVD
who does eGFR not apply to?
- under 18yo
- acute renal failure
- muscle wasting disease
- oedematous state
what is definition of AKI?
- reduction in urine output (<20ml/h)
what is urine urea and urine sodium like in pre-renal failure compared to renal (for AKI)?
- urine urea >500
- urine sodium <10
- urine urea <500
- urine sodium>20
what happens to serum calcium in AKI?
decreases as high phosphate levels inhibits 1alpha hydroxylyase
what happens to serum sodium in AKI?
decreased as losing it
what happens to serum bicarbonate in AKI why?
decreased as using up in acidotic state
what happens to serum potassium in AKI?
tissue catabolism increases K+ - cell lysis
what other blood parameters increase in AKI?
what needs to be measured daily in AKI?
- urine output
- U&E - urea, creatinine, electrolytes
what needs to be measured twice weekly in AKI?
which 5 other tests can you do to determine underlying cause of AKI?
- rhabdomyolysis - CK
- haemolysis - urinary Hb, serum haptoglobin
- myeloma - Ig, paraproteins, BJP
- SLE - ANA, C3, C4 decrease
- DIC - clotting, FDP, d-dimer
what is definition of CKD?
- persistent renal impairment - loss of glomerular and tubular function
- retain nitrogenous waste
what happens to Na and H20 balance early in CKD?
lose it all
what happens to Na and H20 late in CKD?
retain it all
what happens to urine osmolality in CKD?
becomes fixed as tubules not working to concentrate urine
which graph in CKD is linear and what can it predict?
- predict time for RRT
- (any deviation from line - find cause)
how much protein excretion per 24h is abnormal?
what does 1+ on dipstick show?
200-300mg protein in urine
which proteins does urine dip detect and why this is a problem?
- detects albumin
- not BJP for myeloma!
why does cholesterol and triglyceride synthesis increase in nephrotic syndrome?
in low albumin state, liver increases synthetic function and makes more lipoproteins etc
what is RTA?
- metabolic acidosis
- when urine is not well acidified
what is type 1 RTA?
distal - cannot secrete hydrogen ions so get rid of K for Na so low blood K
what is type 2 RTA? so what is Rx?
- proximal - bicarbonate leak. Fanconi syndrome
- Rx replace bicarb
what is type 4 RTA?
- hyporeninemic hyperK hypoaldosteronism
- high K+
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