Diagnostic Highlights


Normal Result

Abnormality with Condition


Serum sodium

136-145 mEq/L

>145 mEq/L

Imbalance between sodium and water lead to excess sodium

Blood urea nitrogen (BUN)

5-20 mg/dL

May be elevated

Conditions that lead to dehydration and fluid loss may elevate BUN because of decreased renal blood flow and abnormal absorption of urea back into the blood

Serum chloride

95-108 mEq/L

>108 mEq/L

Reflects an excess of chloride

Serum osmolarity

280-295 mOsm/L

>295 mOsm/L

Water loss in the urine and hypernatremia lead to hemoconcentration; levels above 320 mOsm/L are considered "panic levels" and require immediate intervention

Urine osmolality

200-1200 mOsm/L

Varies depending on cause; often >800 mOsm/L

Used to diagnose nature of hypernatremia; osmolality refers to a solution's concentration of solute particles per kilogram of solvent; usual renal response to hypernatremia is excretion of maximally concentrated urine (<500 mL/day) with an osmolarity >800 mOsm/L

Other Tests: Complete blood count, urine sodium, serum glucose and protein level, urine specific gravity

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