endocrine and metabolic disorders
Hyponatremia
Diagnosis of Hyponatremia
Measurement of serum and urine electrolytes and determination of osmolality Clinical assessment of volume status Evaluation of renal, adrenal, thyroid, hepatic, and cardiac function Hyponatremia is occasionally suspected in patients who have neurologic abnormalities and are at risk. However, because findings are nonspecific, hyponatremia is often recognized only after serum electrolyte measurement. Serum sodium may be low when severe hyperglycemia (or exogenously administeredmannitolor glycerol) increases osmolality and water moves out of cells into the ECF. Serum sodium concentration falls about 1.6 mEq/L (1.6 mmol/L) for every 100-mg/dL (5.55-mmol/L) rise in the serum glucose concentration above normal. This condition is often called translocational hyponatremia because it is caused by translocation of water across cell membranes. with normal serum osmolality may occur in severe Dyslipidemia , most commonly hypertriglyceridemia, or extreme hyperproteinemia as occurs occasionally with Identifying the cause of hyponatremia can be complex. The history sometimes suggests a cause (eg, significant fluid loss due to vomiting or diarrhea, renal disease, compulsive fluid ingestion, intake of medications that stimulatevasopressinrelease or enhancevasopressinaction). Thevolume status,particularly the presence of obvious volume depletion or volume overload, suggests certain causes (see table). Overtlyhypovolemicpatients usually have an obvious source of fluid loss and typically have been treated with hypotonic fluid replacement. Overtlyhypervolemicpatients usually have a readily recognizable condition, such as heart failure or hepatic or renal disease. Euvolemicpatients and patients with equivocal volume status require more laboratory testing to identify a cause. 275 mOsm/L [mmol/L]) that are low and urine osmolality that is inappropriately high (120 to 150 mmol/L [120 to 150 mOsm/kg]) with respect to the low serum osmolality suggests volume overload, volume contraction, SIADH, or cerebral salt wasting. Volume Overload and 1% (for calculation, see Other urine tests ). In patients with hypovolemia and normal renal function, sodium reabsorption results in a urine sodium of<20 mEq/L (<20 mmol/L). Urine sodium>20 mEq/L (>20 mmol/L) in hypovolemic patients suggests mineralocorticoid deficiency or salt-losing nephropathy. Hyperkalemia suggests adrenal insufficiency. In patients with hyponatremia and a urine sodium of>40 mEq/L (>40 mmol/L) who have recent traumatic brain injury or CNS surgery, cerebral salt wasting should be considered. 