investigations

 Evaluation starts with
o a careful history for new medications
o changes in fluid intake (polydipsia, anorexia, intravenous fluid rates and composition)
o fluid output (nausea and vomiting, diarrhea, ostomy output, polyuria, oliguria, insensible losses)
o The physical examination should help categorize the patient's volume status into hypovolemia, euvolemia, or hypervolemia.

 Symptoms
o Mild - anorexia, headache, nausea, vomiting, lethargy
o Moderate - personality change, muscle cramps and weakness, confusion, ataxia
o Severe - drowsiness

 Signs
These are again highly variable and depend on the level and rate of fall of the serum sodium. They may include:
 Neurological signs
◦ Decreased level of consciousness
◦ Cognitive impairment (e.g. short-term memory loss, disorientation, confusion depression)
◦ Focal or generalised seizures
◦ Brain stem herniation - seen in severe acute Hyponatraemia; signs include coma; fixed, unilateral, dilated pupil, decorticate or decerebrate posturing, respiratory arrest

◦ Signs of hypovolaemia
Dry mucous membranes, tachycardia, diminished skin turgor, and orthostasis suggest hypovolemic hyponatremia due to excessive loss of body fluids and replacement with inappropriately dilute fluids.

◦ Signs of hypervolaemia
Pulmonary rales, S3 gallop, jugular venous distention, peripheral edema, or ascites suggest hypervolemic hyponatremia due to excess retention of sodium and free water (ie, cirrhosis, nephrotic syndrome, congestive heart failure).

◦ Patients who lack findings of hypovolemia or hypervolemia are considered to have euvolemic hyponatremia, which is consistent with such etiologies as exogenous free water load, hypothyroidism, cortisol deficiency, or SIADH.

◦ Other nonspecific signs include muscle weakness and cramping. Rhabdomyolysis is an occasional consequence of hyponatremia and should be considered in patients with muscle pain or tenderness.

 Serum sodium
Before embarking on other investigations for Hyponatraemia, consider whether the sample suffered from dilution by being was taken near the site of an infusion, or whether there is any chance of laboratory error. If necessary, repeat the test. <>300 mOsmol/kg) likely to be due to hyperglycaemia.
◦ Low - (<280 mOsmol/kg) further investigation depends on whether urine sodium is high or low (see Table 1).

 Serum potassium
If raised, consider Addison's. The normal range is 3.7 to 5.2 mEq/L.

 Urine sodium level
Sodium in 24-hour urine collection à Normal: 40–220 milliequivalents (mEq)/day or 40–220 millimoles (mmol)

Increased urinary sodium levels may indicate diuretic use or Addison's disease. Decreased urinary sodium levels may indicate dehydration, congestive heart failure, liver disease, or nephrotic syndrome.

 Imaging
Imaging may be contributory in some clinical situations. For example a chest X-ray may be required in suspected congestive cardiac failure, or a CT brain scan in patients with confusion or altered consciousness.