U&Es Interpretation Flashcards
What is creatinine?
creatinine is a waste product from protein and muscle breakdown
How is creatinine produced?
- Creatine is a substance produced by the liver
- Creatine is phosphylated to make creatine phosphate
- Creatine phosphate is broken down to ATP an creatinine
How is creatinine excreted?
renally
What does one’s baseline creatinine depend on?
Muscle mass
How is urea produced?
The urea cycle converts ammonia (toxic product of deamination reactions of amino acids) to urea in the liver.
How is ammonia produced?
Ammonia is the waste produced by metabolism of nitrogen-containing compounds like proteins and nucleic acids.
How is urea excreted?
Renally
Is serum creatinine or urea more specific for renal function?
Creatinine (BUT urea increases is increased earlier in renal disease)
What can cause increased urea?
- Dehydration
- GI bleed (protein meal)
- Increased protein breakdown e.g. surgery, infection, malignancy
- High protein intake
- Drugs
What can cause decreased urea?
- Malnutrition
- Liver disease
- Pregnancy
What criteria defines an AKI
- Rise in serum creatinine >50% from baseline OR;
- Urine output <0.5ml/kg/hr for 6 hours
Potential investigations in AKI?
- Urine dipstick
- Bloods – FBC, U&Es, CRP, Ca2+, phosphate, PTH
- VBG – check for metabolic acidosis & low bicarbonate, hyperkalaemia
- Accurate fluid balance chart – requires catheterisation
- Stopping of any renal-excreted drugs
Give 2 causes of pre-renal AKI
- Hypovolaemia/sepsis (most common AKI cause)
- Renovascular disease (e.g. renal artery stenosis)
Describe urea vs creatinine level in pre-renal failure
Both increased but increase in urea > increase in creatinine
Since creatinine is not reabsorbed, but is increased only as a result of reduced GFR, plasma urea concentration tends to rise out of proportion to the rise in plasma creatinine concentration in patients with prerenal AKI, and this results in increased BCR/UCR.
Pre-renal failure can cause intra-renal failure. What complication is most commonly seen/
Acute tubular necrosis
Management of pre-renal failure?
IV fluid resuscitation
What is the most common cause of intrinsic renal failure?
Acute tubular necrosis (ischaemic or nephrotoxic)
Give some causes of intrinsic renal failure
- ATN (ischaemic or nephrotoxic)
- Acute interstitial nephritis
- Acute glomerulonephritis
What type of renal failure would haematuria and/or proteinuria suggest?
Intra-renal failure
In a patient’s history, what may suggest intra-renal failure?
- Causative drugs
- Renal hypoperfusion
- Other glomerulonephritis symptoms
- Haematuria
- Proteinuria
Give some investigations for intra-renal failure?
- Urine dipstick
- Urine protein-creatinine ratio
- Possible further tests:
- Nephritic screen (if suspect glomerulonephritis): ANA, ANCA, anti-GBM, RhF, hepatitis serology, anti-phospholipid Ab
- Renal biopsy – unexplained AKI, glomerulonephritis suspected, positive nephritic screen
- Creatinine kinase – if suspect rhabdomyolysis
- Serum bicarbonate
Management for glomerulonephritis?
Immunosuppressants
Main complication of intra-renal failure?
Irreversible renal damage
Cause of post-renal failure?
Urinary tract obstruction (prostate, stones, structure, tumour, blood clots etc)
Describe urea vs creatinine level in post-renal failure
Increased urea = increased creatinine
1st line imaging in post-renal failure?
Renal tract USS
Management of post-renal failure?
Relieve obstruction e.g. catheterise (urinary/suprapubic) if urethral or nephrostomy if ureteric
Main complication of post-renal failure?
Pyelonephritis (can progress to irreversible renal damage)
What criteria defines CKD?
Presence of marker of kidney damage (e.g. proteinuria) OR decreased GFR for >3 months.
Give 5 common causes of CKD
- Diabetes (2ary glomerular disease)
- Chronic HTN
- Chronic glomerulonephritis diseases (e.g. vasculitis)
- Polycystic kidney disease
- Drugs
Investigation for glomerulonephritis?
Kidney biopsy
Give some complications of CKD
- HTN
- Oedema
- Anaemia
- Renal osteodystrophy
- Hyperkalaemia
- Hyperlipidaemia
What critieria indicates the need for dialysis?
- A – Acidosis
- E – Electrolyte abnormalities (e.g. hyperkalaemia, hyponatraemia, hypercalcaemia)
- I – Intoxicants (methanol, lithium, salicism)
- O – Overload (acute pulmonary oedema)
- U – Uraemia
In chronic renal failure, regular dialysis is required when the GFR is <15ml/minute.
Is sodium an extracellular or intracellular ion?
Extracellular
Effect of aldosterone on Na+ and K+?
increases N+ reabsorption and K+ excretion from DCT
Effect of ADH on Na+ and K+?
- Causes reabsorption of H20 (alone) from the collecting duct which dilutes the level of sodium in the body (can lead to hyponatraemia)
- Increases potassium loss into the urine
Give some causes of hyponatraemia in the context of hypovolaemia (i.e. Na+ lost and water follows)
From kidneys:
- Diuretics
- Addison’s disease (increased K+)
- Kidney injury
- Osmotic diuresis
From elsewhere:
- Diarrhoea/vomiting
- Fistula
- Burns
How does diarrhoea/vomiting affect Na+ level?
Hyponatraemia
How do burns affect Na+ level?
Hyponatraemia
Give some causes of hyponatraemia in the context of euvolaemia (i.e. H20 gained and normal Na+)
From kidneys:
- SIADH
- Hypothyroidism
- Glucocorticoid insufficiency
From elsewhere:
- H20 intoxication
How does SIAD affect sodium levels?
Hyponatraemia (due to increased ADH causing dilution of sodium)
How does hypothryoidism affect sodium levels?
Hyponatraemia
Give some causes of hyponatraemia in the context of oedema (i.e. H20 gained and normal Na+)
- Congestive cardiac failure
- Hypoalbuminaemia (e.g. cirrhosis or nephrotic syndrome)
Why does hypoalbuminaemia lead to hyponatraemia?
Hypoalbuminemia causes a shift of fluid from the plasma to the interstitial spaces and a decrease in serum volume, with release of ADH → hyponatraemia
What specific test can be used to test for Addison’s disease?
Synacthen (synthetic ACTH) test or 9am cortisol screening
What specific test can be used to test for SIADH?
Confirmed by combination of low plasma osmolality and high urine osmolality (i.e. low sodium in blood, high sodium in urine)
Management of SIADH?
Fluid restriction
Cause of hypernatraemia in the context of normovolaemia
Iatrogenic (e.g. excess IV crystalloids, sodium containing drugs)
Cause of hypernatraemia in the context of hypovolaemia
- Producing small volumes of concentrated urine (normal response to hypovolaemia)
- Fluid loss → diarrhoea, vomiting, burns
- Not producing small volumes of concentrated urine (abnormal response to hypovolaemia)
- Diabetes insipidus
- Osmotic diuresis (e.g. DKA)
Is potassium intracellular or extracellular?
90% intracellular
Why do H+ and K+ concentrations vary together?
H+ and K+ concentrations vary together because both compete for Na+ symporter in cells and DCT
How does insulin affect K+?
increase cellular K+ uptake by stimulating cellular Na+(in)/K+(out) pumps
How do catecholamines affect K+?
increase cellular K+ uptake by stimulating cellular Na+(in)/K+(out) pumps
How does aldosterone affect K+?
increases Na+(in)/K+(out) pumps in distal convoluted tubule and therefore increases K+ excretion
Give some causes of hypokalaemia due to increased renal excretion
- Diuretics (except K+ sparing)
- Endocrinological – steroids, Cushing’s disease, Conn’s syndrome
- Renal tubular acidosis
- Hypomagnesaemia
How vomiting/diarrhoea affect K+?
Hypokalaemia
Give some causes of hypokalaemia due to increased cellular uptake
- Salbutamol
- Insulin
- Alkalosis
Management of hypokalaemia?
- Treat cause
- Add potassium chloride to IV fluids
Give some causes of hyperkalaemia due to reduced renal excretion
- Acute/chronic kidney injury
- Drugs (K+ sparing diuretics, ACEi, NSAIDs)
- Addison’s disease
How does hypomagnesaemia affect K+?
Causes hypokalaemia
How do NSAIDs affect K+?
Hypokalaemia
Give some causes of hyperkalaemia due to excess K+ load
- Iatrogenic
- Massive blood transfusion
Give some causes of hyperkalaemia due to increased cellular release
- Acidosis
- Tissue breakdown e.g. rhabdomyolysis, haemolysis
ECG changes seen in hyperkalaemia?
- Low flat P waves
- wide bizarre QRS
- slurring into ST segment
- tall tented T waves
Give 4 pharmacological agents that may be used in the management of hyperkalaemia
- Calcium gluconate
- Insulin & glucose
- Salbutamol
- Calcium resonium
How is calcium gluconate effective in managing hyperkalaemia?
- Protects myocytes (required if ECG changes or K+ >6.5)
- Works in minutes
- Lasts 30-60 minutes
How is insulin+glucose effective in hyperkalaemia?
- Temporarily shift K+ into cells
- Check capillary glucose before & after
- Gradually decreases K+
- Lasts 60 mins
Nebulised salbutamol may be added for same effect
What is the only treatment that actually removes K+ from body?
Calcium resonium
Calcium homeostasis:
Give some causes of hypocalcaemia due to increased renal excretion (increased phosphate, increased PTH)
- Drugs (loop diuretics)
- CKD
- Rhabdomyolysis/tumour lysis syndrome
Give some PTH-related causes of hypocalcaemia (increased phosphate, decreased PTH)
- Hypoparathyroidism
- Hypomagnesaemia
- Pseudohypoparathyroidism (resistance to PTH)
- Cinacalcet
Give some causes of hypocalcaemia due to increased deposition/reduced uptake (decreased phosphate, increased PTH)
- Bisphosphonates
- Vitamin D deficiency
How do bisphosphonates affect calclium?
Hypocalcaemia
Management of vitamin D deficiency?
Vitamin D analogues e.g. alfacalcidol
Give some causes of hypercalcaemia
- Decreased renal excretion:
- Drugs (thiazide diuretics)
- Increased release from bones:
- Boney metastasis (increased ALP)
- Myeloma (normal ALP)
- Sarcoidosis
- Thyrotoxicosis
- Excess PTH:
- 1ary hyperparathyroidism (increased PTH) or 3ary hyperparathyroidism (massively increased PTH)
- Excess vitamin D intake
- Dehydration (raised urea & albumin)
How does thyrotoxicosis affect calcium?
Hypercalcaemia
How do bony mets affect calcium?
Hypercalcaemia
How does myeloma affect calcium?
Hypercalcaemia
How does sarcoidosis affect calcium?
Hypercalcaemia
What is hypophosphataemia seen in?
- Vitamin D deficiency
- Refeeding syndrome
- 1ary hyperparathyroidism
- Poor nutrition/alcoholism
How does PTH affect phosphate?
Hypophosphataemia