CP4-3 renal function tests and hydration status Flashcards
What are the 5 main functions of the kidney?
Fluid balance
Removal of waste products from the blood
BP maintenance by balancing Na, K and water
Bone mineralisation (1,25 hydroxy vit D)
RBC production
What is the functional unit of the kidney?
Nephron
What is polyuria?
Urine output >3000ml/24 hours
What volume of urine excretion is normal?
750-2000ml/24hrs
What is oliguria?
Urine output <400ml/24hrs
What is anuria?
Urine output if <100 ml/24hrs
What is the reference range of blood sodium?
133-146 mmol/L
What is the reference range for blood potassium?
3.5-5.3 mmol/L
What is the reference range for blood urea?
2.5-7.8 mmol/L
What is the reference range for blood creatinine?
49-90 umol/L
What can affect how EGFR value is interpreted?
Muscle mass
What tests of renal function should be done when kidney disease is suspected?
Glomerular filtration rate
Estimate EGFR
Creatinine clearance
Plasma creatinine levels
Plasma urea
Assess urine - volume, urea, sodium, protein, glucose, haematuria (can check with urinalysis dipstick test)
What pre-renal factors affect renal function by impairing kidney perfusion?
Cardiac failure
Sepsis
Blood loss
Dehydration
Vascular occlusion
What renal factors affect renal function?
Glumerulonephritis
Small vessel vasculitis
Acute tubular necrosis as a result of drugs, toxins or prolonged hypotension
Interstitial nephritis due to drugs, toxins, inflammatory disease or infection
What post-renal factors affect renal function?
Urinary calculi
Retroperitoneal fibrosis
Benign prostatic enlargement
Prostate cancer
Cervical cancer
Urethral stricture/valves
Meatal stenosis/phimosis
What is the reference range for plasma urea?
3-8 mmol/L
What causes more urea to be reabsorbed into the blood at the glomerulus?
A slow rate of tubular flow
What % of urea is reabsorbed by renal tubules in healthy kidneys?
40%
What causes a slow tubular flow rate in the kidneys?
Renal hypotension
What causes an increased production of urea?
GI bleed
Surgery, infection, trauma
Drugs e.g. steroids and tetracyclines
Cancer
High protein diets
What causes a decreased excretion of urea?
Pre-renal, renal and post-renal factors
What is the reference range for plasma creatinine?
50-140 umol/L (dependent on muscle mass)
What is the relationship between plasma creatinine levels and glomerular flow rate (GFR)?
As concentration of plasma creatinine increase, GFR decreases
Plasma creatinine is not proportional to renal damage. True or false?
True
What is a by product of DKA?
Acetoacetate
Why are plasma creatinine tests inaccurate in patients who have had a paracetamol overdose ?
The overdose is treated with N-acetyl cysteine which makes creatinine levels look like they’ve improved even if they haven’t.
What level may plasma creatinine reach in patients with chronic renal disease?
1000 umol/L
What is a plot of reciprocal plasma creatine concentration used to predict in patients with chronic renal disease?
When intervention for end stage renal failure is required
How is creatinine clearance calculated?
Dividing the urine creatinine concentration (mmol/L) multiplied by the volume of urine (ml collected in 24 hours) by the plasma creatinine (umol/L)
What is the reference range for creatinine clearance?
100-130 ml/min)
What can cause an increased tubular secretion of creatinine?
Chronic renal disease
What can cause tubular secretion of creatinine to be inhibited?
Drugs like salicylate and cimetidine
What are disadvantages of working out creatine clearance?
What does high creatine clearance mean for kidney function?
Good kidney function
What does low creatinine clearance mean about kidney function?
Low kidney function
How does plasma change when creatine clearance is between 30-60ml/min?
increased creatine and urea
How does plasma change when creatinine clearance is between 20-30ml/min?
increased potassium and decreased bicarbonate
How does plasma change when creatinine clearance is between 10-20ml/min?
Increased phosphate and increased uric acid
What caused issues when EGFR was originally introduced?
Calculated using a different formula
Creatine tests are different in different places
How has EGFR been made more reliable?
Standardisation of formula for determining eGFR
What is stage 1 renal function with GFR of 90+?
Normal kidney function
What is stage 2 kidney function with GFR of 60-89?
Mildly reduced kidney function and associated findings of kidney disease
What is stage 3A and 3B kidney function with GFR of 45-59 and 30-44 respectively?
Moderately reduced kidney function
What is stage 4 kidney function with GFR of 15-29?
Severely reduced kidney function requiring planning for end stage renal failure
What is stage 5 kidney function with GFR of <15 or on dialysis?
Very severe or endstage kidney failure aka established renal failure requiring dialysis and transplant
What happens to potassium levels in acute kidney injury?
Potassium levels increase
How can you tell from trends in creatinine levels whether a patient with chronic kidney disease is on dialysis?
The creatinine levels would go down after dialysis and then increase again. If not on dialysis, levels will be stable/won’t fluctuate.
What happens to urea levels when there is an upper GI bleed?
It increases and reduces again when bleeding is stopped.
How can you determine if increased urea on a kidney function test is due to a bleed elsewhere or due to damage to the kidneys?
The increase in urea will be isolated. eGFR will drop due to drop in blood pressure and slight increase in creatinine.
