Urine, Urea, Creatinine

Question 1

Renal causes for haematuria

Answer 1

Congenital: PCK
Trauma
Infection: pyelonephritis
Neoplasm
Immune: GN, TIN

Question 2

Extra-renal causes of haematuria

Answer 2

Trauma: stones, catheter
Infection: cystitis, prostatitis, urethritis
Neoplasm: bladder, prostate
Bleeding diathesis
Drugs: NSAIDs, frusemide, cipro, cephalosporins

Question 3

False positive for haematuria

Answer 3

Myoglobin, porphyria

Question 4

Proteinuria levels

Answer 4

30mg/dL = 1+
300mg/dL = 3+
PCR < 20mg/mM is normal, >300 = nephrotic

Question 5

Causes of proteinuria

Answer 5

DM
Minimal change Membranous
Amyloidosis
SLE

Question 6

False -ve proteinuria

Answer 6

Bence-Jones protein

Question 7

Microalbuminuria

Answer 7

Albumin 30-300mg/24h

Causes: DM, ↑BP, minimal change GN

Question 8

Casts in the urine

Answer 8

RBC: glomerular haematuria
WBC: interstitial nephritis or pyelonephritis
Tubular: ATN

Question 9

Creatinine - determinants of levels, when does plasma Cr increase

Answer 9

Creatinine is synthesised during muscle turnover.
Freely filtered and small proportion secreted by PCT
↑ muscle → ↑ creatinine: age, sex, race
Plasma Cr doesn’t ↑ above normal until 50% ↓ in GFR

Question 10

Urea - production, high levels, low levels, absorption

Answer 10

Produced from ammonia by liver in ornithine cycle ↑ ̄c protein meal (e.g. upper GI bleed, supplements) ↓ ̄c hepatic impairment
10-70% is reabsorbed: depends on urine flow.
↓ flow → ↑ urea reabsorption (e.g. in dehydration)

Question 11

Isolated high urea vs high urea and creatinine

Answer 11

Isolated ↑ urea = ↓ flow (i.e. hypoperfusion / dehydration)

↑ U and ↑ Cr = ↓ filtration (i.e. renal failure)

Question 12

Creatinine Clearance

Answer 12

Vol of blood that can be cleared of a substance in 1min
CrC roughly approximates GFR as it is freely filtered and
only a small proportion secreted (~10%) Slightly overestimates GFR
Requires urine concentration from 24h collection
Can use radiolabelled EDTA: very rarely done

Question 13

eGFR

Answer 13

Modifiation of Diet in Renal Disease (MDRD) equation
Serum Cr, sex, age, race
Obviates need for urine collection

Question 14

Problems - eGFR

Answer 14

Validated for patients ̄c established renal failure: ?applicable to general population.
Most elderly people are in ≥ stage 3 CRF by eGFR: may not progress or impinge on their health.
eGFR is too pessimistic in mild renal impairment