A breast fed child presents with hypernatremia (Serum sodium > 170m Eq/L). His urine sodium is 70 mEq/L. Which of the following is the most likely cause –
(A) Diabetes insipidus (B) Acute necrosis (C) Severe dehydration (D) Excessive intake of sodium
(D) The child is having hypernatremia. Serum sodium >170 rnEq/L (Normal level is 135-145 mEq/L).
Urine sodium is also very high, >70mEq/L (Normal urine sodium level in <20 mEq/L)
This combination can be seen with excessive intake of sodium.
With excessive intake of sodium there will be increase in serum sodium and excessive excretion of sodium in urine (Kidney tries to compensate for increase in serum sodium by excreting large amount of sodium).
Diabetes Insipidus      ->    Serum sodium conc. will be high but urine sodium conc. will be very low (Lack of ADH leads to defect in concentration of urine).
Acute necrosis            ->    Urine sodium conc. will be high but serum sodium conc. will be low. 
Severe dehydration    ->   Urine sodium concentration will be low.