The patient has no significant past medical history. She has never had surgery or been hospitalized for any reason. She does not take any medications and has no known allergies. Her parents are in good health and also have no significant past medical history. She eats a balanced diet, drinks 1 cup of coffee per day in the morning, and does not smoke, drink alcohol, or use illicit substances.

Upon review of systems, the patient admits to dry mouth and dry skin. She admits to constipation for the past several days but denies abdominal pain, nausea, and vomiting. She denies dysuria, urgency, and gross hematuria. The patient denies polyphagia, temperature intolerance, and recent weight loss. The remaining review of systems is negative.

Step 2/3

Clinical Pearl

A good endocrine review of systems requires asking the patient questions that may seem unrelated to one another but are important in reaching a diagnosis. Questions to ask include changes in weight, changes in eating and drinking habits, temperature intolerance, changes in skin and hair, and changes in sweating.

On physical exam, the patient’s blood pressure is 126/85 mm Hg, her pulse rate is 103/min, her respiration rate is 14/min, and her temperature is 37 °C (98.6 °F). She is in no acute distress. Her cardiac exam reveals mild tachycardia, regular rhythm, with clear lung sounds. Her skin is very dry with decreased turgor. Her mucus membranes and lips are dry and her abdomen is soft and nontender. Her lower extremities show no edema with intact pulses.

Urinalysis reveals a urine osmolality of 180 mOsm/kg H₂O with no other abnormal findings. A basic metabolic panel shows a serum osmolality of 295 mOsm/kg, serum sodium of 142 mEq/L, glucose of 96 mg/dL, and calcium of 9.7 mg/dL, with all other values normal, including an absence of protein or glucose in the urine. A complete blood count is normal. The HbA1C is 5.4%.

Step 1

Basic Science Pearl

While the serum sodium in this patient is within the normal range (135 to 145 mEq/L), a value in the upper range of normal can still indicate existing pathology. However, sodium near the upper limit of normal usually does indicate a relative water deficit. Increased serum sodium concentration provides a stimulus for fluid intake to replenish urinary and other losses. Patients who have access to water are usually able to prevent hypernatremia. This is a natural compensatory response.