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what are 2 blood tests of renal function?
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where does urea come from?
made in liver from amino acid break down
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what does excretion of urea depend on?
urinary flow - hence if dehydrated serum urea goes up as less urine flow
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can urea diffuse through dialysis membrane?
yes
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what factors cause plasma urea to go up?
- protein meal - eg GI bleed or steak
- dehydration
- impaired GFR
- catabolic state
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what factors reduce plasma urea?
- starvation
- low protein diet
- liver disease - not making urea
- pregnancy
- SIADH (dilution)
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how is creatinine made? from what?
- product of creatine phosphate turnover in muscle
- small amount from diet
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how is creatinine excreted?
- cleared through glomerulus
- some actively secreted across renal tubule
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what increases serum creatinine?
- reduced GFR
- increased muscle mass
- acute muscle damage
- protein meal
- exercise
- ketones create ARTEFACTUAL rise in Cr due to interference in analysis
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what decreases serum creatinine?
- small muscle mass
- pregnancy
- SIADH
- xs bilirubin
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how do you calculate creatinine clearance?
- UV/P
- urine concentration of creatinine x volume of urine
- divided by
- plasma concentration of creatinine x time period collected in mins
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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
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what is the aim of eGFR and why is this important?
- to pick up EARLY CKD
- as it is a risk factor for CVD
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who does eGFR not apply to?
- under 18yo
- pregnancy
- amputees
- acute renal failure
- muscle wasting disease
- malnourished
- oedematous state
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what is definition of AKI?
- reduction in urine output (<20ml/h)
- reversible
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what is urine urea and urine sodium like in pre-renal failure compared to renal (for AKI)?
- pre-renal:
- urine urea >500
- urine sodium <10
- renal:
- urine urea <500
- urine sodium>20
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what happens to serum calcium in AKI?
decreases as high phosphate levels inhibits 1alpha hydroxylyase
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what happens to serum sodium in AKI?
decreased as losing it
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what happens to serum bicarbonate in AKI why?
decreased as using up in acidotic state
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what happens to serum potassium in AKI?
tissue catabolism increases K+ - cell lysis
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what other blood parameters increase in AKI?
- phosphate
- urea
- creatinine
- potassium
- H+
- urate
- magnsesium
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what needs to be measured daily in AKI?
- urine output
- U&E - urea, creatinine, electrolytes
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what needs to be measured twice weekly in AKI?
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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
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what is definition of CKD?
- persistent renal impairment - loss of glomerular and tubular function
- retain nitrogenous waste
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what happens to Na and H20 balance early in CKD?
lose it all
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what happens to Na and H20 late in CKD?
retain it all
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what happens to urine osmolality in CKD?
becomes fixed as tubules not working to concentrate urine
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which graph in CKD is linear and what can it predict?
- 1/creatinine
- predict time for RRT
- (any deviation from line - find cause)
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how much protein excretion per 24h is abnormal?
>150mg
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what does 1+ on dipstick show?
200-300mg protein in urine
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which proteins does urine dip detect and why this is a problem?
- detects albumin
- not BJP for myeloma!
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why does cholesterol and triglyceride synthesis increase in nephrotic syndrome?
in low albumin state, liver increases synthetic function and makes more lipoproteins etc
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what is RTA?
- metabolic acidosis
- when urine is not well acidified
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what is type 1 RTA?
distal - cannot secrete hydrogen ions so get rid of K for Na so low blood K
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what is type 2 RTA? so what is Rx?
- proximal - bicarbonate leak. Fanconi syndrome
- Rx replace bicarb
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what is type 4 RTA?
- hyporeninemic hyperK hypoaldosteronism
- high K+
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