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104 theme 3 > measurement of renal function > Flashcards

measurement of renal function Flashcards

1
Q

why would you measure renal function.

A

identification of renal impairment

modifying drug dosage (which are cleared by kidneys)

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2
Q

patients at risk of developing renal failure

A

extremes of age
polypharmacy
specific disease states
long term analgesia (NSAIDS nephrotoxic)
transplant patients (rejection, anti rejection drugs)
drug therapy (nephrotoxic - anti biotic/cancer/hiv)
imaging procedures

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3
Q

how does GFR dec with age

A

Matures at 4 years

dec by 0.4-1.2mL/min per year after 40

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4
Q

diseases affecting GFR

A 
hypertension 
diabetes 
chronic HF
rheumatoid arthritis 
renal disease 
recurrent UTIs
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5
Q

how can renal function be monitored

A 
clinical condition (clinical assessment, bedside data)
modern imaging techniques (macroscopic view of renal flow, filtration and excretory functionalists)
biochemical data(renal clearance of substances, evaluate ability to handle water and solutes)
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6
Q

what happens if fluid balance affected

A

oedema - breathlessness

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7
Q

what happens if electrolytes regulation (K, Na, Ca, PO4) are affected

A 
abnormal ECG (absent P waves, broad QRS, peaked T)
absent symptoms
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8
Q

what happens if EPO production is affected

A

pallor - fatigue

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9
Q

what happens with vit D is affected

A

osteomalacia - bone pain

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10
Q

what happens if excretion is effected

A

raised blood creatine and urea conc - pruritis, nausea and vomitting

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11
Q

what happens if acid base balance is affected

A

low blood ph and bicarbonate levels - deep and rapid respiration

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12
Q

what us bedside clinical data

A

weight chart
fluid balance chart
degree of oedema
results of urine dipstick testing (urinalysis for protein, blood, glucose)

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13
Q

what is renography

A

gamma camera planar scintigraphy
positron emission tomography (PET)
single photon emission computerised tomography (SPECT)

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14
Q

what is biochemical data used for

A

identifying renal impairment

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15
Q

what is biochemical data

A

blood (plasma or serum) markers of renal function
plasma or serum creatinine
plasma or serum urea or blood urea nitrogen

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16
Q

what is creatinine

A

breakdown production of creatinine phosphate in muscle
generally produced at constant rate
filtered at glomerulus with some secretion into PT
normal range 40-120 umol/L

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17
Q

what increases plasma creatinine

A 
large muscle mass, diet
drugs with interfere with analysis 
drugs that inhibit tubular secretion 
ketoacidosis
ethnicity (higher if black)
18
Q

what decreases plasma creatinine

A

reduced muscle mass
cachexia/starvation
immobility
pregnancy (due to inc plasma vol of mother)
severe liver disease (liver source of creatinine)

19
Q

how does plasma creatinine indicate renal failure extent

A 
normal 100 (40-120)
normal function up  to 150
mildly reduced 150-300
mod 300-500
sev 500-700
very sev >700
20
Q

what is urea

A

liver produces it in urea cycle as waste product of protein digestion
filtered at glomerulus, sec and abs in tubule
described as BUN
normal 2.5-7.5 mmol/L
>20 sev failure

21
Q

what increases urea

A 
high protein diet
hyercatabolic conditions (eg sev infection, burns)
GI bleeding 
muscle injury 
drugs 
tetracycline 
hypovolaemia
22
Q

what decreases urea

A

malnutrition
liver disease
sickle cell anaemia
SIADH

23
Q

what is biochemical data useful for indicating

A

identifying renal impairment
evaluation of ability of kidneys to handle water and solutes
modifying dodges pf drugs which are cleared by kidneys
some methods measure renal clearance of substances

24
Q

what would an ideal marker of renal function be

A

a naturally occurring molecule
not metabolised
only excreted in kidney
filtered but not secreted or reabsorbed by the kidney

25
Q

what are some examples of renal clearance

A

filtered at glomerulus and not reabsorbed
filtered and some of the filtered portion is reabsorbed
filtered and completely reabsorbed
primarily secreted into tubule

26
Q

what substance is filtered and not reabsorbed

A

Inulin

rate it was filtered - excretion rate

27
Q

what substance is filtered and some reabsorbed

A

electrolytes ex rate= rate filtered - reabsorbed

28
Q

what gets filtered and totally reabsorbed

A 
glucose and AAs
no excretion (normally)
29
Q

what is not reabsorbed and fully secreted

A

PAH

rapidly and effectively cleared

30
Q

what is renal clearance

A

the vol of plasma completely cleared of a given substance in unit time
compares rate og GFR and rate kidneys excrete via urine
allows set of net amount reabsorbed and secreted

31
Q

what does renal clearance provide info about

A 
glomerular filtration (F)
tubular reabsorption (R)
tubular secretion (S)
32
Q

how is renal clearance calculated

A

clearance of x= conc in urine x vol of urine formed in a given time / conc of x in systemic blood plasma or serum
gives overall nephron function

33
Q

what can GFR be used for

A

indicator of renal function
best by measurement of clearance of creatinine but its filtered and secreted into tubule
more accurate - inulin

34
Q

what is inulin

A

plant polysaccharide
freely filtered (not sec or reabs)
so ex in urine = rate of filt in kidneys
=GFR
1mg/ml in plasma then 125mg/ml in urine = GFR 125 ml/min
greater clearance than inulin also being sec, less means reabs or not filtered freely

35
Q

how useful is inulin

A

most reliable but not clinically useful
administered on IV for constant plasma levels
chemical analysis technically demanding
use radio labelled compound instead but may bind to proteins and distort results
creatinine used

36
Q

how his creatinine clearance used

A

filtered at G but also sec into PT
over-estimate GFR by 20% in humans
colorimetry method used underestimates so cancel out

37
Q

how is creatine clearance useful

A

easy, reliable, used clinically
no IV, just venous blood and urine
must account for variables
24hr period to be reliable, samples pre breakfast

38
Q

how can creatinine clearance be used to take into account boost surface

A

corrected creatinine clearance = measured CrCl x 1.73/BSA
BSA - body SA m2
most adults about 1.7m2 (1.6-9)
corrected GFR mL/min/1.73m2

39
Q

how is GFR estimated using plasma creatinine only

A

allows GFR est with no urine
Cockcroft-gault formula
only uses plasma creatinine
Modification of Diet in Renal Disease (MDRD) in UK

40
Q

how does GFR change with kidney function

A

declines as plasma creatinine inc
125- <14 normal to sev
stage kidney disease 1, 2 3a, 3b, 4, 5

41
Q

how can PAH be used to measure renal blood flow

A

not normally present in blood
when given, almost all cleared from kidney in one passage 90%
10% by passes tubule - efferent arterioles to peritubular capillaries to venous renal blood, not sec
blood v urine - effective renal plasma flow

42
Q

what are biomarkers of kidney disease

A 
cr/BUN only inc after sig loss of renal func (eg 60%)
blood and urinary markers released in early renal failure 
eg 
kidney injury molecule u 
IL-18 u 
FABPs u
NGAL p and u
Cystatin C p

104 theme 3 (15 decks)

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