Renal - Urine, Urea And Creatinine

Question 1

Urine - renal causes of haematuria

Answer 1

• Congenital: PCK disease
• trauma
• infection: pyelonephritis
• neoplasm
• immune: GN/TIN

Question 2

Urine - extra renal causes of haematuria

Answer 2

• Trauma: stones, catheter
• infection: cystitis, prostatitis, urethritis
• neoplasm: bladder/prostate
• bleeding diathesis
• drugs: NSAIDs, furosemide, ciprofloxacin, cephalosporins

*Can get false positives from myoglobin or porphyria

Question 3

Proteinuria - commonest causes

Answer 3

• DM
• Minimal change glomerulonephritis
• Membranous glomerulonephritis
• Amyloidosis
• SLE

Other more rare:
-HTN, TIN, UTI, fever

*False negatives: Bence-Jones protein

Question 4

What is microalbuminuria and what are the causes?

Answer 4

• Albumin: 30-300mg/24h in urine

- Causes: DM, HTN, minimal change GN

Question 5

What are the 3 different urine casts indicative of?

Answer 5

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

Question 6

What is creatinine and that is it’s relationship to GFR?

Answer 6

• synthesised during muscle turnover
• freely filtered and small proportion secreted by PCT
• Plasma Cr does not rise above normal until there is a 50% drop in GFR

Question 7

What is urea? What makes it higher/lower and what affects its reabsorption?

Answer 7

• Produced from ammonia by liver in ornithine cycle
• Raised with protein meals (upper GI bleed/supplements)
• Lowered in hepatic impairment
• Re-absorption is dependent on urine flow. Low flow = high urea reabsorption (eg dehydration). Body can reabsorb between 10-70% of urea produced, rest is excreted.

Question 8

How would you interpret

• Isolated raised urea
• Both urea and creatinine raised

Answer 8

• Decreased flow (hypoperfusion/dehydration)

- Decreased filtration- ie renal failure

Question 9

How do you calculate eGFR and what are the problems associated with it?

Answer 9

• Equation based on serum Cr, sex, age and race
• Problems: good for pts with established renal failure (but not as applicable to general population), too pessimistic in mild renal impairment, most old people are in CKD >=3 so eGFR may not be super useful or lead to over Rx