Sketchy Path: Renal Function Tests and AKI

Question 1

Creatinine is the breakdown product of _____________.

Answer 1

creatine (like the creatine meat next to the creatinine credit cards)

Question 2

The normal value of creatinine is _________.

Answer 2

0.6 to 1.2 mg/dL (like the dollar menu)

Question 3

Some creatinine is _____________ in the nephron.

Answer 3

secreted (like the water bottles beneath the meat sign: it is “freely filtered and never reabsorbed!” *but may contain minor secretions)

Question 4

What is GFR?

Answer 4

The amount of fluid that passes into Bowman’s space every minute by all nephrons

Question 5

What is the formula for creatinine clearance?

Answer 5

Clearance = [urine Cr] / [plasma Cr] x volume of urine produced

(Think of the sign pointing to the CUPs… get it?)

Question 6

How does age affect creatinine clearance?

Answer 6

It decreases by 1 ml/min for every year over age 50 (like the older man DROPPING the coffee pot).

Question 7

Where does urea come from?

Answer 7

Protein breakdown (like the N cycle of orders) and pyrimidine breakdown (like the hexagonal tile pattern)

Question 8

What can affect BUN levels?

Answer 8

• Increased protein intake can increase it.
• Decreased liver function can decrease it, because the liver accomplishes the urea cycle.
• Decreased kidney clearance can increase it.

Question 9

Unlike creatinine, urea is __________________ in the nephron.

Answer 9

partially absorbed by the PCT

Think of the BUN grease that has been absorbed by the waiter’s shirt with the Pro Cart Track logo on it.

Question 10

AKI can be either _________________.

Answer 10

prerenal, renal, or postrenal

Question 11

What are the two classic signs of acute kidney injury?

Answer 11

Sudden oliguria and creatinine elevation (like the empty cup near the credit card slip)

Question 12

What causes prerenal azotemia?

Answer 12

Decreased perfusion to the kidneys, such as after hemorrhage or during profoundly decreased cardiac output (like the hemorrhaging ketchup and the boy with the floppy heart balloon)

Question 13

What serum values suggest prerenal azotemia?

Answer 13

• BUN:Cr ratio greater than 15 (like how the BUN is held higher than the credit card)
• FENa less than 1% (like the one falling fry basket)
• Increased urine osmolality (like the pepper that has fallen over and is concentrating the mustard)

All of these occur because the kidney is trying to absorb more water and sodium.

Question 14

What is FENa?

Answer 14

The percent of sodium excreted over the percent creatinine excreted x 100.

Question 15

What are some common causes of intrinsic AKI?

Answer 15

• Acute tubular necrosis (straw with chocolate milk)
• Interstitial nephritis (blue kidney tray)
• Glomerulopathies (red curly straw)

Question 16

The BUN:Cr ratio in intrinsic kidney injury is _____________.

Answer 16

usually less than 15 (like how the BUN bag is only slightly higher than the credit card as they fall off the table)

Question 17

What is the FENa of intrinsic AKI?

Answer 17

Greater than 2% (like how the kid has two baskets of fries on his head)

Question 18

The urine osmolality in intrinsic AKI is ______________.

Answer 18

low (like how the OSM mustard is empty on the table)

Question 19

Why does azotemia occur from post-renal blockage?

Answer 19

Pressure builds up and GFR decreases

Question 20

What lab values are typical of post-renal azotemia?

Answer 20

• Elevated BUN:Cr ratio (like the firefighter’s elevated BUN bag over the creatinine credit card)
• The other values aren’t as reliable, but in general, post-renal azotemia can progress to intrinsic kidney damage if prolonged enough and have the same values (like the BUN and credit card on the ground by the firefighter’s feet)

Question 21

What can cause post-renal azotemia?

Answer 21

• BPH (like the BPH firefighter)
• Bilateral kidney stones (like the kid shooting two spit balls)
• Urinary tract cancer (like the crab belt buckle over his crotch)