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Clinical Pathology > Tests of renal function > Flashcards

Tests of renal function Flashcards

1
Q

What happens if the input of a solute increases and the excretion stays constant?

A

The concentration of the solute will rise.

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2
Q

What happens if the input of a solute decreases and the excretion stays constant?

A

The concentration of the solute will fall.

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3
Q

What happen if the excretion decreases and the input stays constant?

A

The concentration will rise.

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4
Q

What happens to the concentration of a solute during water overload?

A

The concentration will fall. The reverse happens during water deprivation.

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5
Q

What are the functions of the kidney?

A
  • excretion e.g. urea, uric acid
  • regulation e.g. homeostasis, water, acid base
  • endocrine e.g. renin, erythropoietin
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6
Q

What is the purpose of renal function tests?

A
  • detect renal damage
  • monitor functional damage
  • distinguish between impairment and failure
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7
Q

Where are the three places problems can arise in the urinary tract?

A
  • Pre-renal - Renal - Post-renal
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8
Q

What are the possible causes of renal failure?

A
  • Pre-renal e.g. decreased ECFV or MI - Renal e.g. acute tubular necrosis - Post-renal e.g. ureteral obstruction
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9
Q

What are the different kinds of laboratory test of renal function?

A
  • glomerular filtration rate - eGRF - estimate - creatinine clearance - plasma creatinine - plasma urea - urine volume - urine urea - urine sodium - urine protein - urine glucose - haematuria
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10
Q

What urine volume over 24h is normal in health?

A

750 - 2000ml/24h

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11
Q

What urine volume over 24h is seen in oliguria?

A

>80ml but <400ml

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12
Q

What urine volume over 24h is seen in anuria?

A

>100ml

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13
Q

What urine volume over 24h is seen in polyuria?

A

>3000ml/24h

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14
Q

What is the value of the plasma urea test?

A
  • quick, simple measurement
  • wide reference range 3 - 8 mmol/L
  • sensitive but non-specific index of illness
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15
Q

What factors affect plasma urea concentration?

A
  • GIT protein and tissue protein -> liver amino acids
  • Distribution volume
  • Kidney reabsorption excretion
  • Kidney filtration
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16
Q

Where is urea excreted?

A

Filtered at the glomerulus

17
Q

What percentage of filtered urea is reabsorbed by renal tubules in health?

A

40%

18
Q

Is more or less urea reabsorbed if the rate of tubular flow is slow?

A

More

19
Q

Why would tubular flow rate be slow?

A

Renal hypoperfusion

20
Q

What might be the causes of increased plasma urea?

A
  • GI bleed - trauma
  • renal hypoperfusion decreased RBF decreased ECFV
  • acute renal impairment
  • chronic renal disease
  • post-renal obstruction calculus tumour
21
Q

What is the value of the urea test?

A
  • Useful test but must be interpreted with great care
  • Always consider input, output and patient’s fluid volume
22
Q

What are the features the plasma creatinine test?

A
  • 50 - 140 umol/L
  • increases in concentration as GFR decreases
  • analytical interferences (acetoacetate - DKA)
  • NOT proportional to renal damage
  • Change within an individual patient is usually more important than the absolute value
23
Q

What is usually more important than the absolute value in a plasma creatinine test?

A

Change within an individual patient

24
Q

What predicts when intervention is required in end stage renal failure?

A

Plot of reciprocal of plasma creatinine concentration against time.

25
Q

Under what circumstances would GFR be measured?

A
  • Kidney donors
  • Calculating drug dose
26
Q

How is creatinine clearance (Ccreat) calculated?

A

Ccreat = Ucreat/Pcreat x V

Ucreat = urine creatinine conc (mmol/L)

V = urine volume (ml collected in 24hr)

Pcreat = plasma creatinine conc (umol/L)

27
Q

In health how much higher is creatinine clearance than GFR?

A

10-30%

28
Q

Which drugs inhibit tubular secretion?

A
  • salicylate
  • cimetidine
29
Q

What condition increases tubular secretion?

A

Chronic renal disease

30
Q

Is creatinine clearance a reliable test?

A

No

31
Q

What is stage 1 kidney failure?

A
  • GFR = 90+ - Normal kidney function but urine findings, structural abnormalities or genetics point to kidney disease
  • Treatment - Observation, control of blood pressure
32
Q

What is stage 2 kidney failure?

A
  • GFR = 60-89
  • Mildly reduced kidney function and other findings (as for stage 1) point to kidney disease.
  • Treatment - observation, control of BP and risk factors
33
Q

What is stage 3 (A&B) kidney failure?

A
  • GFR (3A) = 45-59
  • GFR (3B) = 30-44
  • Moderately reduced kidney function
  • Treatment - observation, control of BP and risk factors
34
Q

What is stage 4 kidney failure?

A
  • GFR = 15-29
  • Severely reduced kidney function
  • Treatment - planning for end-stage renal failure

Clinical Pathology (65 decks)

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