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Introduction to Biochemistry > Assessment of renal function > Flashcards

Assessment of renal function Flashcards

1
Q

how many people in the UK have CKD?

A

~3.5 million people

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2
Q

how many people are on dialysis

A

30,000

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3
Q

what % of NHS budget is spent on dialysis and transplantation?

A

2-3% 2.4 billion

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4
Q

what are the symptoms of kidney disease?

A

hypertension - swollen ankles, high BP, headaches, visual disturbances
changes in urinary frequency/volume
in stage 4 and 5 (too late - very poor prognosis) - fatigue, nausea, vomiting, poor appetite, shortness of breath, fluid retention
reduction of 50-60% functional renal mass may occur before any signs or biochemical abnormalities manifest.
regular monitoring of those at risk therefore very important CVD, HT, DM genetically as risk individuals.

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5
Q

how many stages of CKD?

A

5

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6
Q

laboratory investigations of renal function

A

imaging
histology and microscopy
immunology
biochemistry (urinalysis, quantitative biochemical markers)

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7
Q

what imaging may be used

A

US or CT/MRI
imaging of kidney. bladder, ureters, prostate gland
size/symmetry/obstruction to urine flow anywhere
main disadvantages: expensive, difficult to assess extent of functional damage cant see nephrons in detail

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8
Q

main disadvantages of a biopsy?

A

rarely used unless specific condition
invasive
only a snapshot

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9
Q

what immunology tests helpful for renal function?

A

complement - low c4 seen in SLE and cryoglobulinaemia
anti-glomerular basement antibodies: associated with Goodpasture’s disease (kidney and lung disease)
cANCA- associated with vasculitis esp. Wegener’s disease
pANC: associated with vasculitis

main disadvantage - only useful in specific diseases

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10
Q

what is urine defined as

A

fluid excreted by the kidneys, passed through the ureters, stored in bladder and discharged through urethra

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11
Q

what are the characteristics of urine in health?

A

sterile
clear
amber
slightly acidic
pH 5.0-6.0
characteristic odour

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12
Q

what is anuria

A

<100ml/24hrs
lack of urine production

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13
Q

what is oliguria?

A

<400ml/24hr
one of the earliest signs of impaired renal function

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14
Q

what is polyuria?

A

> 3L/24h or >50mL/kg mass/24h

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15
Q

what is glucose in the urine a key sign of?

A

diabetes

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16
Q

are urine test strips qualitative or quantiative?

A

qualitative

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17
Q

limitations of urinalysis (dipstick)

A

potential for operator error
inter-operator variability, even with automation
requires fresh urine, in date, properly stored dipsticks
poor sensitivity and specificity - sensitivity depends on concentration of urine

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18
Q

what can interfere with urinalysis?

A

blood analysis - menstruation (+ve), vit C (-ve) - from the ascorbic acid
protein analysis - infected urine (+ve), dilute urine (-ve)

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19
Q

quantitative biochemical measurements for glomerular filtration/function?

A

urea
creatinine
proteinuria

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20
Q

quantitative biochemical measurements for tubular function

A

urine volume / osmolality
pH
phosphate
aminoaciduria
glycosuria
b2-microglobulin

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21
Q

quantitative biochemical measurements for fanconi syndrome

A

phosphate
aminoaciduria
glycosuria

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22
Q

ideal markers of glomerular function

A

freely filtered
not reabsorbed
not secreted
not metabolised
not synthesises in the renal tubules/kidney

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23
Q

measuring glomerular function: exogenous markers?

A

measure rate at which they ace cleared

inulin ‘gold standard’
- metabolically inert sugar, provides good GFR estimation
BUT (disadvantages)
- non-endogenous (IV administration)
- assay not widely available
- expensive

I-Iothalamate
Cr-EDTA
DTPA
Iohexol

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24
Q

assessing glomerular function endogenous markers

A

urea - end product of nitrogenous compound metaboliSm (esp amino acids), freely filtered at glomerulus
BUT
some passive reabsorption in renal tubules
raised in GI bleeds/high protein diets, low in liver disease

Creatinine: product of muscle metabolism, fairly constant rate of production, removed by glomerular filtration

cystatin C- small protein produced by all nucleated cells - not affected by muscle mass, age, gender or race. affected by thyroid function and some drugs.

NGAL (neutrophil gelatinase associated lipocalin) ‘ up and coming’ marker of AKI

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25
Q

Serum/plasma creatinine for assessing glomerular function

A

quick, cheap and convenient
interferences (e.g. Jaffe method - ketones, bilirubin)
- most labs now use enzymatic assays-still affected by bilirubin
GFR falls to <50ml/min before creatinine rises

26
Q

what is the glomerular filtration rate?

A

thought to be the most reliable measurement of functional capacity, it roughly indicates the number of functioning nephrons. most sensitive and specific marker of changes in overall renal function.

27
Q

Fall in GFR

A

Increase in plasma/serum creatinine (cant filter into ultra filtrate for urine)
decrease in urine creatinine i.e. reduced creatine clearance

28
Q

work out GFR from creatinine clearance using…

A

urine creatinine (in 24 hr period)
serum/plasma creatinine (single sample at same time)

29
Q

equation for creatinine clearance

A

CrCl ml min-1 = urine creatinine mmol/L x urine vol (mL) divided by plasma/serum creatinine mmol/L x time (min) UV/PT

30
Q

how to collect a 24hr urine

A

day 1 8am empty bladder (discard output)
commence 24hr urine collection - all urine now passed until 8am next day must be collected into container
day 2 8am collect final urine output into container
blood sample to accompany urine

31
Q

estimated eGFR variables

A

serum creatinine
age
sex
ethnicity (no longer used)

now use CKD-EPI equation

32
Q

limitations of the CKD-EPI equation, not to be used in

A

AKI
CHILDREN
PREGNANCY
MALNOURISHED
OEDEMATOUS STATES
MUSCLE WASTING DISEASES
AMPUTEES

33
Q

Assessing glomerular function - proteinuria

A

24hr protein excretion <0.15g/24hr
protein loss >3g/24h can result in ‘nephrotic syndrome’

albumin:creatinine ratio (ACR) (<3mg/mmol)
dont have to do 24hr urine
can use PCR (protein:creatinine ratio) but ACR is preferred as it is more sensitive at low levels

microalbumin (ability to detect albumin at low levels in urine)

urinary sediment
RBC, hyaline, casts
RBC casts imply haemoglobinuria because of glomerular disease

34
Q

example of overflow proteinuria

A

BJP

35
Q

example of glomerular proteinuria

A

albuminuria

36
Q

example of tubular proteinuria

A

B2 or a1 microglobulins

37
Q

example of secreted proteinuria

A

Tamm-Horsfall proteinuria

38
Q

what does proteinuria occur in kidney disease as a result of?

A

increases in filtered blood (increased glomerular vascular permeability)
decrease in reabsorptive capacity (due to tubular damage)

39
Q

what is glomerular proteinuria

A

increased permeability means that larger proteins are excreted, e.g. albumin, IgG NON-SELECTIVE

40
Q

what is tubular proteinuria?

A

decreased reabsorption of the freely filtered small proteins (e.g. RBP). these then appear in relatively higher quantities than albumin in the urine.

RBP= retinol binding protein

41
Q

PCR and ACR limitations

A

assumptions
- urine output 1.5L
- creatinine excretion 10mmol/day
- binary gender: male/female (not transgender)

42
Q

assess tubular function by monitoring electrolytes…potassium

A

often high due to low GFR = inability of excretion. can be low in some conditions

43
Q

assess tubular function by monitoring electrolytes…sodium

A

can be low/high/normal. often used to assess fluid status

44
Q

assess tubular function by monitoring electrolytes…calcium

A

often low due to defective 1a hydroxylation of vitamin D which takes place in the kidney

45
Q

assess tubular function by monitoring electrolytes…po4 and mg

A

often high fur to low GFR=inability of excretion (however are sometimes low due to increased renal losses especially post-Tx)

46
Q

what is CKD

A

abnormalities of kidney function or structure present for more than 3 months with implications for health

includes all people with markers of kidney damage and those with a GFR<60ml/min/1.73m2 on at least 2 separate occasions separated by a period of at least 90n days with / without markers of kidney damage

47
Q

normal GFR

A

150 ml/min

48
Q

annual GFR check

A

on pts taking meds that can adversely affect kidney function

49
Q

nice CKD recommendations

A

do not eat meat in the 12 hrs before having blood test for eGFRcreatinine
interpret eGFRcreatinine with caution in extremes of muscle mass e.g. body builders, amputees, muscle wasting disorders

50
Q

GFF G1 category GFR >90ml/min

A

normal

51
Q

GFR G2 60-89

A

mildly decreased

52
Q

g3a GFR 45-59

A

mild to moderately decreased

53
Q

g3b egfr 30-44

A

moderately to severely decreased

54
Q

g4 gfr 15-29

A

severely decreased

55
Q

g5 gfr <15

A

kidney failure

56
Q

ACR CKD categories

A

ACR1 <3mg/mmol normal to mildly increased
ACR2 3-30mg/mmol moderately increased
ACR3 >30mg/mmol severely increased

diabetes mellitus:
ACR<2.5mg/mmol
ACR<3.5mg/mmol

57
Q

to be classed as having CKD

A

ACR greater than 3 and or GFR less than 60

58
Q

how should AKI pts be monitored

A

monitor people for the development or progression of CDK for at least 2-3years after AKI even if serum creatinine has returned to baseline

59
Q

AKI stage 1

A

serum creatinine - increase > or equal to 26umol/L within 48hrs or increase > or equal to 1.5 to1.9 x reference Scr

urine output- <0.5ml/kg/hr for >6 consecutive hours

60
Q

AKI stage 2

A

serum creatinine - increase > or equal to 2 to 2.9 x reference SCr

urine output - <0.5ml/kg/hr for > 12 hrs

61
Q

AKI stage 3

A

creatinine - increase > or equal to 354umol/L or increase > or equal to 3 x reference Scr or commenced on renal replacement therapy

urine output- <0.3ml/kg/hr for >24 hours or anuria for 12 hours

62
Q

what is the reference serum creatinine

A

the lowest creatinine value recorded within 3 months of the event. if a reference serum creatinine is not available within 3 months and AKI is suspected repeat serum creatinine within 24 hours. reference serum creatinine can be estimated from the nadir serum creatinine if patient recovers from AKI

Introduction to Biochemistry (6 decks)

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