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Chemical Pathology > Renal Function > Flashcards

Renal Function Flashcards

1
Q

Name the 3 categories of proteinuria

A

• Benign (most)
• persistent proteinuria ≥1+: early sign CKD eg diabetes nephropathy, ht, gn
• proteinuria >300 mg/day

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2
Q

Normal amount of urine protein?

A

<150mg/day

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3
Q

What are the components of urine protein?

A

• 20% LMW proteins eg IGS
• 40% HMW albumin
• 40% tubular mucoproteins

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4
Q

Define microalbuminuria

A

30-300 mg/day or 20-200 ug / min

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5
Q

What does microalbuminuria indicate?

A

Early nephropathy eg screen for diabetic nephropathy

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6
Q

Name 4 mechanisms of proteinuria and name the proteins involved

A

• Overflow:high plasma conc of lmw protein eg myoglobin in crush injury, Bence Jones protein (myeloma), immunoglobulin light chains in myeloma
• glomerular Proteinuria (2-3g/day): increased glomerular permeability eg albumin!, immunoglobulins
= heavy proteinuria, indicate CKD (DM, glomerular disease, HT)
• tubular (LMW: <2g/day) : impaired/saturated reabsorption eg alpha 1 microglobulin, retinol binding protein!, beta 2 microglobulin
• secretory: secreted by kidneys or unitary tract epithelium eg immunoglobulins with UTI or bladder tumour.

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7
Q

What is creatinine?

A

By product of energy metabolism thus production depends on muscle mass

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8
Q

Name 6 causes elevated creatinine

A

. Severe damage to nephrons eg AKI (very sensitive)
• massive rhabdomyolysiss /crush injury
• diet eg red meat excess
• patient stature ey body builder, adult men
• drugs: probenecid, cimetidine, trimetoprime, amiloride (block tubular secretion)
• analytical interference: cephelasporine and ketone bodies cause interference with lab assay

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9
Q

Name 4 causes low creatinine

A

• Elderly and infants
• chronic illness
• Lab analytical interference: high bilirubin - falsely low
• vegetarians: no creatinine in diet

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10
Q

How is creatinine clearance calculated

A

Clearance = ( urine creatinine X urine flow rate[ml/min or L/24h/1.44) ÷ plasma creatinine
Ml/min (/m2 if corrected for BSA)

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11
Q

Best measure of renal function?

A

GFR

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12
Q

Normal creatinine clearance?

A

Adult male 90-140 ml/min
Adult female 80-125

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13
Q

Grading of decreased creatinine clearance?

A

Mild decrease GFR: 60-89 ml/min
Moderate: 30-59
Severe: 15 (need dialysis because more creatinine in serum, not being cleaned)

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14
Q

How is plasma creatinine related to the GFR?

A

Inversely proportional

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15
Q

MDRD equation to calculate eGFR?

A

175 x (sCr x 0,011312)^-1.154 x age^-0.203

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16
Q

Define the criteria for chronic kidney disease (2)

A

• Kidney damage for ≥ 3 months as defined by structural or functional abnormalities of kidney, with or without decreased GFR manifested either by
-Pathological abnormalities or
- markers of kidney damage including abnormalities in blood or urine composition, or imaging
Or
• GFR <60 ml/min/1,73m^2 for ≥ 3 months with or without kidney damage

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17
Q

Which 4 variables does the MDRD equation for egfr take into account

A

•creatinine
• Age
• ethnicity
• Gender

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18
Q

Name 9 situations in which eGFR can be misleading

A

• AKI
• increased volume of distribution for creatinine eg oedema of heart failure or nephrotic syndrome
• pregnancy
. Decreased or increased muscle mass
• extremes of age
• ethnic groups
• malnutrition and obesity
• meat rich meal
• drugs that interfere with renal secretion of renal tubules

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19
Q

What is the Cockcroft Gault formula?

A

• Provides estimate of creatinine clearance and thus GFR, not commonly used
• variables: body weight, sex, age, serum creatinine

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20
Q

What is cystatin c?

A

• Small protein produced by all nucleated cells
• freely filtered by glomerulus and completely reabsorbed and catabolized by pct cells
• better accuracy than creatinine: not influenced by sex or muscle, single reference range for all adults under 50, more practical for monitor GFR changes in paediatrics

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21
Q

Name 3 factors that may increase cystatin c

A

• Malignancy
• hyperthyroidism
• corticosteroid treatment

22
Q

Why is cystatin c a useful test?

A

• Sensitive screening test for early assessment of changes in e gfr
• plasma concentration reflects GFR more accurately than creatinine
(But more expensive so not in public )

23
Q

Which formula is best to use for CkD screening?

A

Ckd-epi formula.
Use serum creatinine, sex, race, cystatin C
(But expensive)

24
Q

How is beta 2 microglobulin B2M used? (3)

A

• Good for GFR measurement, similar to serum creatinine
• urine B2M very sensitive indicator of renal tubular disease
• not specific, but sensitive for various neoplastic, inflamm, infective conditions
• prognostic marker in multiple myeloma

25
Q

How is urea made?

A

Synthesized in liver as byproduct of deamination of amino acids

26
Q

Name 3 uses of urea measurement

A

• Effect of EcF volume (dehydration, CCF etc )
• protein intake and catabolism
• renal blood flow
(Less specific than creatinine for renal function)

27
Q

What do urea levels out of proportion to creatinine indicate

A

Pre renal failure eg dehydration

28
Q

At what point in renal failure will urea be elevated?

A

Only when > 60% nephrons no longer functioning

29
Q

Name 8 extra renal causes of high urea : creatinine

A

• High protein intake
• git bleeding
• hypercatabolic state
• dehydration
• CCF
• urinary stasis
• muscle wasting
• amputation

30
Q

Name 3 extra renal causes of low urea : creatinine

A

• Low protein intake
. Dialysis
• severe liver disease

31
Q

How calculate fractional excretion of Na (fena)

A

100 x (una x pcr) ÷ (pna x ucr)

32
Q

How calculate renal function index (rfi)

A

(Una x pcr) ÷ Ucr

33
Q

What will urine na, Fe Na (fractional excretion of sodium), RFI, urea: creatinine, urine osmolality be in pre-renal disease

A

urine na: low (<20)

Fe Na:low (<1%)

RFI: low (<1%)

urea: creatinine: high (>70)

urine osmolality: concentrated (>500)

34
Q

What will urine na, Fe Na, RFI, urea: creatinine, urine osmolality be in renal disease ATN

A

urine na: high. (>40)

Fe Na: high (>1%)

RFI:high (>1%)

urea: creatinine: low (<70)

urine osmolality: dilute (<350)

35
Q

What will urine na, Fe Na, RFI be in post renal disease

A

urine na: high (>40)

Fe Na:ver yhigh (>4%)

RFI: high (>1%)

36
Q

Name 2 limitations to urea: creatinine ratio > 70 (high urea)

A

(In pre renal disease)
• common finding in elderly
• marker of ill health

37
Q

Name 2 limitations to fe Na < 1 % (as marker of prerenal disease)

A

• Diuretics increase excretion of filtered Na
• In secondary hyperaldosteronism (as in cirrhosis), Na excretion decreased

38
Q

Name 6 pre-renal causes AKI

A

(Decreased blood flow to kidneys)
• dehydration
• hypotension
• haemorrhage
• septicaemia
• low cardiac out put
• burns

39
Q

Name 6 intrinsic renal causes AKI

A

Specific renal diseases and systemic disease affecting kidneys
• rapidly progressive glomerulonephritis
• SLE, vasculitis

Nephrotoxin’s
• NSAIDs
• aminoglycocydes
• xr contrast media, plant toxins, some anti cancer drugs

Intrarenal obstruction eg Bence Jones protein

Renal ischaemia secondary to hypoperfusion, leading to “Acute tubular necrosis” (old name)

Sepsis, severe haemorrhage, burns, radial failure

40
Q

Name 5 post renal causes AKI

A

• Bilateral obstructing kidney stones
• prostatic enlargement
• other urinary tract neoplasms
• retroperitoneal fibrosis involving both ureters
• neurogenic bladder

Obstruction to flow of urine leads to increase in hydrostatic pressure in collecting ducts → oppose glomerular filtration → secondary renal tubular damage if prolonged
Obstruction above urethral insertion into bladder must be bilateral to have major effect on urine flow

41
Q

How is AKI staged

A

Use creatinine and urine output

42
Q

Name 10 biochemical plasma changes in AKI

A

• Increase potassium
• increase p
• increase mg
• increase hydrogen ion (acidosis)
• increase urea
• increase urate (uric acid)
• increase creatinine

. Decrease sodium
• decrease calcium
• decrease bicarb

(Same in CKD, except urate )

43
Q

Nb what is the urine sodium concentration, urine: plasma urea, urine :plasma osmolality in pre-renal AKI

A

urine sodium concentration: <20 mmol/l

urine: plasma urea > 20:1

urine :plasma osmolality > 1,5:1

44
Q

Nb what is the urine sodium concentration, urine: plasma urea, urine :plasma osmolality in intrinsic AKI

A

sodium concentration >40 mmol/l

urine: plasma urea < 10:1

urine :plasma osmolality <1,1:1

45
Q

Name 2 biomarkers useful to identify patients at high risk of progression to intrinsic kidney injury

A

• Urine kidney injury molecule 1
• Neutrophil gelatinase associated lipocalcin

46
Q

Name 4 effects of CKD on the endocrine system

A

• Calcitriol synthesis
• decreased testosterone, oestrogen synthesis
• abnormalities TFT - not usually clinical thyroid disease, but high incidence goitre and primary hypothyroid in ckD
• abnormal glucose tolerance with hyperiensulinaemia caused by insulin resistance (however diabetics on insulin have decreased insulin requirements after CKD, because insulin metabolised in kidney)

47
Q

What type of anaemia is present in CKD and why? (3)

A

• normochromic normocytic anaemia of chronic disease
• depression bone marrow function by retained toxins
• decrease renal production erythropoietin

48
Q

Name 6 clinical features of CKD

A

• Neurological: lethargy, peripheral neuropathy
• dermal: pruritis, pallor, purpura
• musculoskeletal: growth fail, bone pain, myopathy
• cardiovascular: anaemia, ht, pericarditis
• git: anorexia, hiccough, nv, git bleeding
. Genitourinary: nocturia, impotence

49
Q

How is CKD staged?

A

GFR and albuminuria

50
Q

Why do creatinine clearance

A

Use Cockcroft-Gauls equation.
For use in pts with stable renal function. Approximates the calculation of eGFR (cheaper)

Chemical Pathology (23 decks)

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