32.5 Lab tests of renal function Flashcards

1
Q

What are the functions of the kidney? (3)

A

Regulation of water, homeostasis and acid-base.
Excretion of urea and uric acid.
Endocrine: renin, erythropoietin, 1,25-dihydroxycholecalciferol.

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2
Q

Which laboratory tests measure renal function? (10).

A

Glomerular filtration rate.
Plasma creatinine and creatinine clearance.
Plasma urea.
Urine volume, urea, sodium, protein, glucose.
Haematuria.

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3
Q

What is the urine volume in oliguria?

A

Less than 400ml/24hr.

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4
Q

What is the urine volume in anuria?

A

Less than 100ml/24hr.

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5
Q

What is the urine volume in polyuria?

A

More than 3000ml/24hr

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6
Q

Where is urea excreted?

How much is reabsorbed and where?

A

Glomerulus.

40% in the renal tubules.

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7
Q

What are the common causes of increased plasma urea? (5)

A
Acute/chronic renal impairment.
Post renal obstruction.
Renal hypo-perfusion.
GI bleed.
Trauma.
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8
Q

How is creatinine clearance calculated?

A

(urine creatinine conc x urine volume) / plasma creatinine conc

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9
Q

What are the common causes of pre-renal oliguria? (4)

A

Haemorrhage.
Dehydration.
Renal artery damage.
Hypotension.

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10
Q

What changes to lab results are seen in pre-renal oliguria? (3)

A

GFR reduced.
ADH increased.
Low sodium in urine.

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11
Q

What changes to the lab results are seen in renal oliguria? (4)

A

GFR reduced/normal.
Weak urine/low volume.
Raised renin secretion - hypertension.
High sodium in urine.

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12
Q

When does plasma creatinine increase?

When is it useful?

A

When GFR decreases.
Change within a patient over time. Predicts need for intervention in end stage renal failure. Not proportional to renal damage.

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13
Q

Which drugs decrease tubular secretion of creatinine? (2)

A

Salicylate.

Cimetidine.

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14
Q

What does clearance of [99Tc]-Sn-DTPA measure?

A

Glomerular filtration rate.

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15
Q
What are the GFR values for: 
Normal kidney function
Mildly reduced,
Moderately reduced
Severely reduced
End stage kidney failure?
A
90+
60-89
30-45
15-29
Less than 15/on dialysis.
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16
Q

What are the causes of renal oliguria? (4)

A

Tubular necrosis.
Chronic infection.
Immunological damage.
Toxic: drugs, heavy metals (Hg, Ur), poisons (paraquat).