Clinical Evaluation

Question 1

3 Ways to Use Creatinine to Meas GFR

Answer 1

1- Meas serum creatinine (blood draw) BUT varies by muscle mass (dec muscle mass due to underlying disease may dec creatinine)

2- Meas creatinine clearance (24 urine collection + blood)

- calc GFR = UV/Plasma
- Con - sometimes people over or under-collect (must check b/f); and creatinine is secreted so clearance will always be >> GFR

3- Estimation equation using serum creatinine (blood draw)

- Cockroft-Gault - dep on age and body weight (so may over-estimate in obese - muscle mass not proportional to weight); mult by .85 for women (mainly for dosing)
- MDRD - tends to under-estimate in normal population
- CKD-EP - newer

Question 2

Why can’t creatinine be used in AKI? What do we use instead?

Answer 2

• Creatinine no longer at steady state
• Abrupt loss of creatinine filtration - inc serum creatinine
• Instead, meas rise in serum creatinine/BUN and dec urine output to eval changes in function
• BUN:creatinine ratio

Question 3

BUN (what is it and what 4 things does it tell us?)

Answer 3

(blood urea nitrogen)

• Also used to assess kidney function but less reliable for GFR b/c reabsorbed and varies

TELLS US

- Protein intake
- Catabolism - inc BUN
- Liver function - cirrhosis --> less BUN prod
- Vol status - more reabsorption of low vol

Question 4

Proteinuria (what is normally in urine? what does high value tell us? What protein do we specifically look for?)

Answer 4

• Uromodulin - protein in urine; secreted by TAL
• Should not have high levels of filtered proteins in urine b/c reabsorbed in proximal tubule
• If high proteinuria…
  
  • Proximal tubule dysfunction
  • Damage to filtration barrier (let larger molecules get taken up into tubules)
  • Inc production of small peptides (ex - in cancer) overwhelms system
• Usually meas via albumin levels in urine (more sensitive
  than total protein)
• # 1 factor in prognosis of ongoing kidney disease (aka when dialysis is needed)

Question 5

Specific Gravity

Answer 5

roughly correlates w/ osmolality (urine conc)

Question 6

9 Things to Look for on Urine Dipstick

Answer 6

1- pH - high in UTI; may help dx stones

2- Proteins -Normally proteinuria not detected unless HIGH

3- Blood - underlying renal problem

4- Glucose - DM

5- Ketones - DM (ketoacidosis or starvation)

6- Urobilinogen - produced in gut from metabolism of bilirubin so changes if jaundice; if obstructive jaundice then dec; if not obstructive then in

7- Bilirubin - if inc production or dec hepatic uptake (liver disease)

8- Nitrite - prod by gram neg bacteria in UTI

9- Leuks - UTI (infection)

Question 7

4 Things to Look for on Microscopic Urine Analysis

Answer 7

1 CELLS- RBCs (hematuria), WBCs (infection), tubular or epithelial squamous cells (shed if injury)

2- CASTS; trap whatever cells are being shed
- RBC, WBC, granule casts

3- CRYSTALS

4- Micro-organisms

Question 8

5 Urine Crystals

Answer 8

• Calcium oxalate - ethylene glycol OD
• Uric acid crystals (low pH)
• Cystine crystals (low pH and always pathological)
• Triple phosphate crystals - associated w/ infection (urea splitting bacteria)
• Calcium carbonate (high pH)