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Clinical Pathology > CP4-3 renal function tests and hydration status > Flashcards

CP4-3 renal function tests and hydration status Flashcards

1
Q

What are the 5 main functions of the kidney?

A

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

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2
Q

What is the functional unit of the kidney?

A

Nephron

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3
Q

What is polyuria?

A

Urine output >3000ml/24 hours

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4
Q

What volume of urine excretion is normal?

A

750-2000ml/24hrs

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5
Q

What is oliguria?

A

Urine output <400ml/24hrs

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6
Q

What is anuria?

A

Urine output if <100 ml/24hrs

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7
Q

What is the reference range of blood sodium?

A

133-146 mmol/L

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8
Q

What is the reference range for blood potassium?

A

3.5-5.3 mmol/L

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8
Q

What is the reference range for blood urea?

A

2.5-7.8 mmol/L

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9
Q

What is the reference range for blood creatinine?

A

49-90 umol/L

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10
Q

What can affect how EGFR value is interpreted?

A

Muscle mass

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11
Q

What tests of renal function should be done when kidney disease is suspected?

A

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)

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12
Q

What pre-renal factors affect renal function by impairing kidney perfusion?

A

Cardiac failure
Sepsis
Blood loss
Dehydration
Vascular occlusion

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13
Q

What renal factors affect renal function?

A

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

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14
Q

What post-renal factors affect renal function?

A

Urinary calculi
Retroperitoneal fibrosis
Benign prostatic enlargement
Prostate cancer
Cervical cancer
Urethral stricture/valves
Meatal stenosis/phimosis

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15
Q

What is the reference range for plasma urea?

A

3-8 mmol/L

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16
Q

What causes more urea to be reabsorbed into the blood at the glomerulus?

A

A slow rate of tubular flow

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17
Q

What % of urea is reabsorbed by renal tubules in healthy kidneys?

A

40%

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18
Q

What causes a slow tubular flow rate in the kidneys?

A

Renal hypotension

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19
Q

What causes an increased production of urea?

A

GI bleed
Surgery, infection, trauma
Drugs e.g. steroids and tetracyclines
Cancer
High protein diets

20
Q

What causes a decreased excretion of urea?

A

Pre-renal, renal and post-renal factors

21
Q

What is the reference range for plasma creatinine?

A

50-140 umol/L (dependent on muscle mass)

22
Q

What is the relationship between plasma creatinine levels and glomerular flow rate (GFR)?

A

As concentration of plasma creatinine increase, GFR decreases

23
Q

Plasma creatinine is not proportional to renal damage. True or false?

A

True

24
Q

What is a by product of DKA?

A

Acetoacetate

25
Q

Why are plasma creatinine tests inaccurate in patients who have had a paracetamol overdose ?

A

The overdose is treated with N-acetyl cysteine which makes creatinine levels look like they’ve improved even if they haven’t.

26
Q

What level may plasma creatinine reach in patients with chronic renal disease?

A

1000 umol/L

27
Q

What is a plot of reciprocal plasma creatine concentration used to predict in patients with chronic renal disease?

A

When intervention for end stage renal failure is required

28
Q

How is creatinine clearance calculated?

A

Dividing the urine creatinine concentration (mmol/L) multiplied by the volume of urine (ml collected in 24 hours) by the plasma creatinine (umol/L)

29
Q

What is the reference range for creatinine clearance?

A

100-130 ml/min)

30
Q

What can cause an increased tubular secretion of creatinine?

A

Chronic renal disease

31
Q

What can cause tubular secretion of creatinine to be inhibited?

A

Drugs like salicylate and cimetidine

32
Q

What are disadvantages of working out creatine clearance?

A
33
Q

What does high creatine clearance mean for kidney function?

A

Good kidney function

34
Q

What does low creatinine clearance mean about kidney function?

A

Low kidney function

35
Q

How does plasma change when creatine clearance is between 30-60ml/min?

A

increased creatine and urea

36
Q

How does plasma change when creatinine clearance is between 20-30ml/min?

A

increased potassium and decreased bicarbonate

37
Q

How does plasma change when creatinine clearance is between 10-20ml/min?

A

Increased phosphate and increased uric acid

38
Q

What caused issues when EGFR was originally introduced?

A

Calculated using a different formula
Creatine tests are different in different places

39
Q

How has EGFR been made more reliable?

A

Standardisation of formula for determining eGFR

40
Q

What is stage 1 renal function with GFR of 90+?

A

Normal kidney function

41
Q

What is stage 2 kidney function with GFR of 60-89?

A

Mildly reduced kidney function and associated findings of kidney disease

42
Q

What is stage 3A and 3B kidney function with GFR of 45-59 and 30-44 respectively?

A

Moderately reduced kidney function

43
Q

What is stage 4 kidney function with GFR of 15-29?

A

Severely reduced kidney function requiring planning for end stage renal failure

44
Q

What is stage 5 kidney function with GFR of <15 or on dialysis?

A

Very severe or endstage kidney failure aka established renal failure requiring dialysis and transplant

45
Q

What happens to potassium levels in acute kidney injury?

A

Potassium levels increase

46
Q

How can you tell from trends in creatinine levels whether a patient with chronic kidney disease is on dialysis?

A

The creatinine levels would go down after dialysis and then increase again. If not on dialysis, levels will be stable/won’t fluctuate.

47
Q

What happens to urea levels when there is an upper GI bleed?

A

It increases and reduces again when bleeding is stopped.

48
Q

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?

A

The increase in urea will be isolated. eGFR will drop due to drop in blood pressure and slight increase in creatinine.

Clinical Pathology (65 decks)

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