Wallach's Interpretation of Diagnostic Tests: Pathways to Arriving at a Clinical Diagnosis (1221 page)

   Increased number of Heinz bodies (e.g., postsplenectomy)

   Increased number of nucleated RBCs

   Some rare Hb variants, such as HbC Harlem or C Georgetown

SODIUM (Na)

   Definition

   Sodium is the major extracellular cation and exerts a major influence on plasma osmolality. It plays a central role in maintaining the normal distribution of water and osmotic pressure. Changes in serum sodium most often reflect changes in water balance rather than sodium balance. It is adjusted by antidiuretic hormone (ADH) secretion and the thirst receptors to maintain plasma osmolality and volume. Aldosterone causes tubular reabsorption of sodium. Atrial natriuretic peptide hormone decreases sodium reabsorption.

   Use

   Diagnosis and treatment of dehydration and overhydration. If a patient has not received large load of sodium, hypernatremia suggests need for water, and values <130 mEq/L suggest overhydration.

   Electrolyte, acid–base balance; water balance; water intoxication.

   
Normal range:
135–145 mmol/L.

   Critical values: <121 or >158 mmol/L.

Increased In

   Conditions associated with water loss in excess of salt loss through the skin, lungs, GI tract, and kidneys

   Dehydration—inadequate fluid intake to replace dermal, respiratory, or GI loss of fluid

   GI causes: vomiting or diarrhea