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Flashcards in Tests of renal function Deck (34):
1

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

The concentration of the solute will rise.

2

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

The concentration of the solute will fall.

3

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

The concentration will rise.

4

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

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

5

What are the functions of the kidney?

- excretion e.g. urea, uric acid

- regulation e.g. homeostasis, water, acid base

- endocrine e.g. renin, erythropoietin

6

What is the purpose of renal function tests?

- detect renal damage

- monitor functional damage

- distinguish between impairment and failure

7

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

- Pre-renal - Renal - Post-renal

8

What are the possible causes of renal failure?

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

9

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

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

10

What urine volume over 24h is normal in health?

750 - 2000ml/24h

11

What urine volume over 24h is seen in oliguria?

>80ml but <400ml

12

What urine volume over 24h is seen in anuria?

>100ml

13

What urine volume over 24h is seen in polyuria?

>3000ml/24h

14

What is the value of the plasma urea test?

- quick, simple measurement

- wide reference range 3 - 8 mmol/L

- sensitive but non-specific index of illness

15

What factors affect plasma urea concentration?

- GIT protein and tissue protein -> liver amino acids

- Distribution volume

- Kidney reabsorption excretion

- Kidney filtration

16

Where is urea excreted?

Filtered at the glomerulus

17

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

40%

18

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

More

19

Why would tubular flow rate be slow?

Renal hypoperfusion

20

What might be the causes of increased plasma urea?

- GI bleed - trauma

- renal hypoperfusion decreased RBF decreased ECFV

- acute renal impairment

- chronic renal disease

- post-renal obstruction calculus tumour

21

What is the value of the urea test?

- Useful test but must be interpreted with great care

- Always consider input, output and patient’s fluid volume

22

What are the features the plasma creatinine test?

- 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

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

Change within an individual patient

24

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

Plot of reciprocal of plasma creatinine concentration against time.

25

Under what circumstances would GFR be measured?

- Kidney donors

- Calculating drug dose

26

How is creatinine clearance (Ccreat) calculated?

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

In health how much higher is creatinine clearance than GFR?

10-30%

28

Which drugs inhibit tubular secretion?

- salicylate

- cimetidine

29

What condition increases tubular secretion?

Chronic renal disease

30

Is creatinine clearance a reliable test?

No

31

What is stage 1 kidney failure?

- GFR = 90+ - Normal kidney function but urine findings, structural abnormalities or genetics point to kidney disease

- Treatment - Observation, control of blood pressure

32

What is stage 2 kidney failure?

- 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

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

- GFR (3A) = 45-59

- GFR (3B) = 30-44

- Moderately reduced kidney function

- Treatment - observation, control of BP and risk factors

34

What is stage 4 kidney failure?

- GFR = 15-29

- Severely reduced kidney function

- Treatment - planning for end-stage renal failure

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