Hyponatremia laboratory findings

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Saeedeh Kowsarnia M.D.[2]

Overview

In hyponatremia, depending on the cause, there can be different laboratory abnormalities.

To see the causes of hyponatremia, click here.

To see the differential diagnosis of hyponatremia, click here.

Laboratory Findings

Biochemical evaluation for finding the etiologies of hyponatremia :

CT scan for brain chest abdomen and pelvis is necessary for patients to evaluate the causes like SIAD( tumor detection ), and differentiate from other causes with the same presentation.

For different causes of hyponatremia, click here.

For approach to differential diagnosis, click here.

For the clinical approach to diagnosis, click here.

Laboratory findings in different causes of hyponatremia ^[1]:

Conditions	Sodium status	Plasma osmolality	Urine osmolality	Differentiation of causes
Hypervolemic hyponatremia	TBW ↑↑ Serum Na ↑	< 275 mOsm/kg	> 100 mOsm/kg	U_Na > 20 mEq/L: Acute or chronic renal failure Fluid overload Psychogenic polydipsia Diuretic use in: Heart failure , Liver disease, Nephrotic syndrome U_Na < 20 mEq/L: Heart failure Primary polydipsia Cirrhosis Nephritic/nephrotic syndrome
Euvolemic hyponatremia	TBW ↑ Serum Na ↔	< 275 mOsm/kg	> 100 mOsm/kg	Variable U_Na : SIAD/ SIADH with fluid restriction Hypothyroidism U_Na > 40 mEq/L: Cortisol deficiency ACTH deficiency Hypothyroidism Drugs SIAD/ SIADH
Hypovolemic hyponatremia	TBW ↔ Serum Na ↓↓	< 275 mOsm/kg	> 500 mOsm/kg	U_Na > 30 mEq/L: Renal loss: Osmotic diuresis (glucose, urea, bicarbonaturia) Salt-Iosing nephropathy Addison disease CSW Diuretics U_Na < 30 mEq/L: Diuretics Extra renal loss: Vomiting (U_cl ↓) Diarrhea Pancreatitis Sweating Small bowel obstruction

References

↑ Wiebke Fenske, Sebastian K. G. Maier, Anne Blechschmidt, Bruno Allolio & Stefan Stork (2010). “Utility and limitations of the traditional diagnostic approach to hyponatremia: a diagnostic study”. The American journal of medicine. 123 (7): 652–657. doi:10.1016/j.amjmed.2010.01.013. PMID 20609688. Unknown parameter |month= ignored (help)

Overview