Interpretation of Urine Electrolytes and Osmolality Mnemonics

Question 1

What does a low FEₙₐ indicate in prerenal AKI?

Answer 1

FEₙₐ <1%

Indicates that the cause of AKI is likely due to inadequate blood flow to the kidneys.

Question 2

What does a high FEₙₐ indicate in ATN?

Answer 2

FEₙₐ >2%

Indicates that the cause of AKI is likely due to intrinsic kidney damage.

Question 3

What exceptions exist for low FEₙₐ in certain conditions?

Answer 3

CHF, cirrhosis, contrast, rhabdo

In these cases, FEₙₐ may still be low despite the presence of ATN.

Question 4

What does a positive urine anion gap (Uₐɢ) indicate?

Answer 4

Distal RTA

Positive Uₐɢ occurs when Na⁺ + K⁺ > Cl⁻, indicating decreased NH₄⁺ production.

Question 5

What does a negative urine anion gap (Uₐɢ) indicate?

Answer 5

Diarrhea

Negative Uₐɢ occurs when Na⁺ + K⁺ < Cl⁻, indicating increased NH₄⁺ production.

Question 6

How do you differentiate between renal and extrarenal loss of potassium?

Answer 6

K⁺ <15 = Outside, >20 = Kidney

Uₖ/Uᶜᵣ <15 suggests extrarenal loss (GI loss or poor intake), while >20 suggests renal loss.

Question 7

What does FEᵤᵣₑₐ <35% indicate?

Answer 7

Hypovolemia

This suggests low blood volume, even in patients on diuretics.

Question 8

What urine osmolality pattern is associated with Diabetes Insipidus?

Answer 8

≤100 mOsm/kg

Indicates dilute urine production due to inadequate ADH action.

Question 9

What urine osmolality pattern is associated with SIAD?

Answer 9

> 200 mOsm/kg

Indicates concentrated urine production due to excess ADH action.

Question 10

What urine osmolality pattern is typical for prerenal AKI?

Answer 10

> 400 mOsm/kg

Indicates the kidneys are conserving water due to low blood flow.

Question 11

What does positive electrolyte-free water clearance (Cᴇʜ₂ᴏ) indicate?

Answer 11

Hypernatremia

Indicates water loss and a need for increased water intake.

Question 12

What does negative electrolyte-free water clearance (Cᴇʜ₂ᴏ) indicate?

Answer 12

Hyponatremia

Indicates water retention and dilution of serum sodium.

Question 13

What does FEᴜᴀ >10% suggest in the context of hyponatremia?

Answer 13

SIAD or Cerebral Salt Wasting

Indicates that the kidneys are losing sodium despite low serum sodium levels.

Question 14

What urine specific gravity indicates normal concentration?

Answer 14

> 1.020

Suggests euvolemia and adequate kidney function.

Question 15

What urine specific gravity indicates dilute urine?

Answer 15

<1.005

Indicates conditions like Diabetes Insipidus or polydipsia.

Question 16

What does the mnemonic ‘CHART’ represent for causes of hyponatremia?

Answer 16

C: CHF, H: Hypothyroidism, A: Adrenal insufficiency, R: Renal failure, T: Thiazides/SIAD

Helps recall common causes of hyponatremia.