Case Studies

Patient presents with intense thirst and polyuria

Na+: 152 mmol/L

Serum osmolarity: 310 mOsm/kg

Urine Osmolarity: 80 mOsm/kg

What disorder explains this pattern?

• diabetes insipidus

  • high sodium and serum osmolarity with inappropriately dilute urine = inability to concentrate urine

70 year old presents with confusion

Na+: 121 mmol/L

Serum osmolarity: 258 mOsm/kg

Urine osmolarity: 600 mOsm/kg

What condition explains these findings?

• SIADH

  • low serum osmolarity with inappropriately concentrated urine

A patient with severe diarrhea has:

Na+: 140 mmol/L

Cl-: 12 mmol/L

HCO3-: 18 mmol/L

This pattern represents?

• Normal anion gap acidosis

  • bicarbonate loss is compensated by chloride retention (hyperchloremia)

A patient has iron studies as:

serum iron ↓

TIBC ↑

Ferritin ↓

MCV ↓

What is the diagnosis

• Iron deficiency anemia

Patient has altered mental status

Na+: 138 mmol/L

Glucose: 80 mg/dL

BUN: 12 mg/dL

Measured osmolarity: 345 mOsm/kg

What additional finding is most likely?

• elevated osmolal gap

  • the large difference between measured and calculated values = elevated osmolar. gap = unmeasured osmoles