What is the role of lab testing in the workup of severe dehydration?

Updated: Dec 07, 2018
  • Author: Lennox H Huang, MD, FAAP; Chief Editor: Timothy E Corden, MD  more...
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With severe dehydration, the following laboratory studies are suggested:

  • Serum sodium should be determined because hyponatremia (150 mEq/L) require specific treatment regimens.

  • Potassium may be elevated (eg, congenital adrenal hyperplasia, renal failure, marked acidosis) or low (eg, pyloric stenosis, alkalosis).

  • Chloride may be low in pyloric stenosis (eg, hypochloremic, hypokalemic, or metabolic alkalosis) or tubercular meningitis.

  • Poor tissue perfusion in dehydration results in production of lactic acid. Bicarbonate is consumed as lactic acid levels increase. In diabetic ketoacidosis (DKA), ketoacids also consume bicarbonate. Bicarbonate levels can also be reduced because of loss of bicarbonate in diarrheal stools. Low bicarbonate levels have been correlated with increased severity of dehydration in some studies.

  • Glucose may be dangerously low because of poor intake or low absorption, or extremely elevated in DKA.

  • BUN and creatinine levels may be elevated because of renal hypoperfusion; prerenal state.

  • Urine specific gravity may be elevated in patients with dehydration but should not be relied on because it is not an accurate diagnostic test for dehydration. [12] Further caution should be used in the setting of diabetes insipidus, in which the urine is dilute with low specific gravity, even in patients who are dehydrated.

  • Urinalysis may show findings of DKA (eg, ketones, glucose).

  • Electrolyte analysis of any fluid that is lost (eg, urine, stool, gastric fluid) can be performed to further refine the composition of replacement fluids after providing acute fluid resuscitation.

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