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laboratory tests of renal function Flashcards

1
Q

for solutes what happens if the input increases and the excretion stays constant?`

A

the concentration will rise and vice versa

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2
Q

what happens if the input of a solute stays the same but the output decreases?

A

the concentration will rise and vice versa

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3
Q

what is incorporated in a healthy state?

A

not just what is being excreted and ingested but also what is being produced in the body

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4
Q

what can be used as a marker for compromised excretion rate in the kidney?

A

rise in urea - if urea is constant but the excretion decreases then it rises

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5
Q

for solvents what will happen if the volume increases or decreases?

A

the concentration will rise when there is a decreased volume of solvent and vice versa
e.g. higher concentration in water deprivation and lower in water overload

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6
Q

what feeds into body volume?

A

intake and metabolic production and excretion feeds out

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7
Q

what does concentration of a solute depend on?

A

amount of the solute present and the volume of water in which it is dispersed

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8
Q

what are the three main functions of the kidney and give examples?

A

excretion - urea and uric acid
regulation - homeostasis, water, acid and base
endocrine - renin and erythropoietin

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9
Q

what is erythropoietin for?

A

for maintaining Hb levels

25 hydroxycholecalciferol to 1,25 dihydroxycholecalciferol which is vit D

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10
Q

what is involved in regulation?

A

helps with compensatory mechanisms

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11
Q

what are the processors and the filters of the kidney?

A

the processors are the tubules and the filter is the glomerulus

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12
Q

where does the input arterial and the output venous go from and to?

A

input arterial into the glomerulus

output venous out of the tubules

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13
Q

what are renal function tests for?

A

detecting renal damage, monitor functional damage and distinguish between impairment and failure

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14
Q

what happens when there is renal damage?

A

function is impaired

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15
Q

how can we monitor functional damage?

A

physical and functional are connected so can do through blood in urine or proteins

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16
Q

what is the therapy with failure?

A

dialysis and eventually transplant

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17
Q

what are the classifications of renal damage?

A

pre-renal
renal
post-renal
the distinctions will determine the treatment

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18
Q

how can we assess kidney damage?

A

clinical symptoms
tests
urine output - often overlooked

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19
Q

what is normal for urine output?

A

40ml/hour

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20
Q

what are causes of pre renal damage?

A

decreased ECFV or MI
MI results in low BP meaning that there is not enough blood flow to kidney and therefore little filtration as is not driven through the glomerulus

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21
Q

what is a cause of renal damage?

A

acute tubular necrosis - major injury will results in a BP drop so there is ischaemia in the tubules - this will regenerate if it is not severe

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22
Q

what are causes of post renal damage?

A

ureteral obstruction
can be from seriously enlarged prostate bladder, bladder cancer, peritoneal fibrosis (sticks to back wall) or cancer of the ureter or wrong tubes being tied

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23
Q

what lab tests are there to assess renal damage?

A

GFR, eGFR, creatinine clearance, plasma creatinine, plasma urea, urine excretion, volume, urea, sodium, protein, glocuse and haematuria

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24
Q

what is GFR used?

A

is is seldom used in clinical practice unless a very accurate measure is needed such as in donors or dose of drugs
it is the clearance of [99Tc]-Sn-DTPA

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25
Q

what are the characteristics of creatinine clearance?

A

in health this will be 10-30% higher than GFR
there are problems with incomplete collection as when out of house is difficult
unreliable as use wrong flow time or part of flow
there is a 1000 fold difference in units
is done ideally over 24 hours

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26
Q

what increases and inhibits tubular secretion of creatinine?

A

it is increased in chronic renal disease

drugs such as salicylates such as cimetidine and aspirin inhibit the secretion

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27
Q

how can you calculate creatinine clearance from a set period of time?

A

measure the amount of creatinine excreted in fixed time period and calculate using the plasma creatinine conc and therefore can calculate how much plasma has passed through kidney to produce this
clearance = urine creatinine con (mmol/L) x volume of creatinine (ml over 24 hours) /plasma creatinine conc (micromol/L)

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28
Q

what is the reference range for creatinine clearance?

A

100-130ml/min

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29
Q

how would you calculate the creatinine clearance from results?

A

scatter plot with line of best fit
y axis of 1/[pCreat]
x axis of time

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30
Q

what are the characteristics of plasma creatinine?

A

the reference ranges of plasma creatinine are 50-140 micromol/L
increase in concentration as GFR decreases
not proportional to renal damage
analytical interferences
is the measure of acetoacetate - DKA
chemical reaction is method - cheap but not accurate
non linear change

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31
Q

why can GFR not be measured against the change is plasma creatinine?

A

the change is not proportional
in chronic renal disease PC may increase to 1000 micromol/L
the creatinine may also still be in the reference range but the GFR may have plummeted as well as function

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32
Q

what needs to be considered when using plasma creatinine to measure function?

A

in terms of the reference range and individual in hand

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33
Q

what can be used to measure GFR and PC?

A

a reciprocal graph

predicts when intervention is required in end stage renal failure - dialysis and transplant

34
Q

what interferes with the chemical reaction?

A

other chemicals can affect it and therefore are aiming for enzymatic method

35
Q

what is important to consider with patients graphs?

A

change within an individual patient is usually more important than the absolute value

36
Q

what are the characteristics of plasma urea?

A

it is a quick simple measurement with a wide reference range of 3-8mmol/L
it is a sensitive but non specific index of illness
as renal reabsorption decreases then urea is amplified - can be useful or over exaggerate

37
Q

what else can affect plasma urea?

A

protein (tissue or GIT) - breaking down tissue protein such as in surgery or damage to muscles making urea
AA - when they are deaminated and the constituents are urea - used for nitrogen metabolism - protein intake will increase
distribution volume - anything that changes the water volume and then changes urea and function filtration rate
kidney filtration, reabsorption and excretion

38
Q

what is the urine volume reference range per 24 hours?

A

750-2500mL/24 hours

in health

39
Q

what is oliguria?

A

<400mL

this is the minimum volume that is needed to produce in order to remove toxic metabolites

40
Q

what is anuria ?

A

<100 - failure to produce urine - depends on the time of day and activities

41
Q

what is polyuria?

A

it is >3000

in syphilis and diabetes where there is little ADH

42
Q

what are the characteristics of urea excretion?

A

urea is filtered at the glomerulus and around 40% is reabsorbed at the renal tubules in health

43
Q

what happens when there is renal hypoperfusion?

A

the tubular flow rate is slower meaning that more urea is reabsorbed

44
Q

what is an early phase of pre renal failure?

A

there is early high urea

45
Q

in chronic kidney disease what is the change to plasma as the creatinine clearance changes:

a) 60-120
b) 30-60
c) 20-30
d) 10-20?

A

a) no change in plasma
b) increased creatinine and urea
c) increased potassium and decreased bicarbonate
d) increased phosphate and uric acid

46
Q

when could plasma urea increase?

A

chronic renal disease, acute renal impairment, renal hypoperfusion, trauma, GI bleed, post-renal obstruction

47
Q

what is an example of post - renal obstruction?

A

calculus, tumour

slows filtration as there is back pressure

48
Q

why does renal hypoperfusion increase urea?

A

there is decreased ECFV and RBF

49
Q

what is an example of a GI bleed that will increase urea?

A

gastric ulcers - feed into GIT and push the area up

50
Q

what is needed to be considered for urea?

A

the input, output and the patient’s fluid volume

always interpret with care

51
Q

in current practice how is eGFR calculated?

A

it is calculated in the lab using an international formula by taking creatinine and estimating

52
Q

what were the initial problems of this method of eGFR?

A

there is variance between labs in chemical methods
ethnicity impacts
different formulas are used
need to compensate for the patients weight
creatinine will test different in different places

53
Q

how were the initial issues identified with eGFR overcome?

A

it is now classified into bands - more standardised and reliable

54
Q

what equation does the UK use for eGFR?

A

it uses the abbreviated MDRD equation

186(creatinine /88.4) - 1.154(age) - 0.203(if female x0.742 and if black then 1.210)

55
Q

what does the grade of eGFR determine?

A

the methodology of referral from GP and the treatment

56
Q

what is stage 1 and 2 in terms of eGFR findings?

A

1 - eGFR of 90+
stage 1 means that the kidney function is normal but urine, structural abnormalities or genetic traits point to kidney disease and therefore is managed with observation and control of BP
2 - eGFR of 60-89 meaning that the function is mildly impaired and other findings point to kidney disease - the treatment is observation, management of risk factors and blood pressure

57
Q

describe stage 3 of eGFR and its divisions?

A

there are stages 3a and 3b
3a will have an eGFR of 45-59 and 3b of 30-44. The treatment is observation and control of BP and RFs and there is moderate reduced kidney function

58
Q

what is stage 4?

A

it is an eGFR of 15-29. The kidney function is severely reduced and there is planning for end stage kidney failure

59
Q

what is stage 5?

A

the eGFR of less than 15 or on dialysis. It is very severe - endstage/established renal failure. The treatment choices are dialysis or transplant

60
Q

what is the result of pre renal oliguria?

A

the GFR is reduced

61
Q

when might ADH be increased?

A

when we are dehydrated - the urine concentration is high with low volume

62
Q

what is needed for pre renal oliguria?

A

IV fluids and saline - need water and sodium

63
Q

what are causes of low renal perfusion?

A 
dehydration 
strictures
post operative lack of fluid 
haemorrhage 
renal artery damage 
hypotension
64
Q

what is a result of renal hypoperfusion?

A

renin secretion

65
Q

what is the result of renin secretion from hypoperfusion?

A

functioning nephrons will increase the sodium absorption through the release of aldosterone and urine concentration of sodium is therefore low

66
Q

what is the main cause of pre renal oliguria and what is the difference between renal and pre renal?

A

the main cause of pre renal is hypoperfusion

renal is a reduced urine volume that implies AKI

67
Q

what are the characteristics of renal oliguria?

A

GFR is reduced or normal and there is concentrated urine with low volume
cannot reabsorb sodium
intrinsic damage

68
Q

why is the renal renin secretion raised in renal oliguria?

A

unable to reabsorb Na but need to

this results in hypertension from angiotensin and the urine sodium concentration remaining high above 40mmol/L

69
Q

what can cause renal oliguria?

A

intrinsic damage
tubular necrosis which is reversible if not too sever
chronic infections
immunological damage such as in SLE
toxic damage such as drugs, heavy metals and poisons
hypertension is the main cause

70
Q

what is the sodium concentration of urine in PR?

A

<20mmol/L

71
Q

what is the P/U urea ratio?

A

> 5 fold in PRU

<2 fold in RRF

72
Q

what are other clues for renal renal failure?

A

from urine - anaemia, haematuria, proteinuria, urine casts

73
Q

what are other problems of renal renal failure?

A

the calcium and phosphate resulting in metabolism disorders and bone disease

74
Q

how can we figure out which stage of the kidney process is affected?

A

through urine sodium and urine tests

75
Q

what is renal failure?

A

when there is fluid in but nowhere to go resulting in oedematous and cardiac overload and failure - need dialysis to overcome

76
Q

what is the treatment consideration for dialysis?

A

balancing the input and overload

77
Q

which lab test of renal function is often forgotten?

A

urine volume

78
Q

what are the plasma lab tests for renal function?

A

plasma creatinine, urea and sodium

79
Q

what are the urine tests for renal function?

A

urea, volume and sodium and dipsticks

80
Q

what else can be done with creatinine to identify renal problems?

A

creatinine clearance

81
Q

what are the issues of the lab tests?

A

creatinine clearance is unreliable
GFR is impractical
plasma urea is subject to problems
plasma creatinine is specific but it is insensitive

CP (38 decks)

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