Dehydration Workup

Updated: Dec 07, 2018
  • Author: Lennox H Huang, MD, FAAP; Chief Editor: Timothy E Corden, MD  more...
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Laboratory Studies

No definitive laboratory test for dehydration is available. Laboratory data are generally not required if the etiology is apparent and mild-to-moderate dehydration is present.

With severe dehydration, the following laboratory studies are suggested:

  • Serum sodium should be determined because hyponatremia (< 130 mEq/L) and hypernatremia (> 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.



Intravenous line

If severe dehydration is present, peripheral intravenous line insertion may be difficult. The preferred sites for initial insertion attempts include the basilic and cephalic veins in the antecubital fossa and the saphenous veins near the ankle. Transillumination of the insertion site with a fiberoptic light source may be used to facilitate locating the desired vein.

If peripheral intravenous access cannot be rapidly achieved (< 90 s) in a child with severe dehydration and shock, intraosseous cannulation should be attempted. If the child is not in extremis, more time may be taken to establish central venous access percutaneously (eg, femoral, subclavian, internal, external jugular).

Intraosseous line

Intraosseous cannulation can be easily and rapidly achieved in children younger than 6 years. Specially designed intraosseous infusion needles or Jamshidi-type bone marrow aspiration needles may be used. Short large-bore spinal needles may also be used but often bend during placement. The ideal site of insertion is the anteromedial surface of the tibia, 1-3 cm below the anterior tibial tuberosity. Care must be taken to avoid injury to the physeal growth plate.

Orogastric/nasogastric tube

An orogastric/nasogastric tube may be inserted to facilitate enteral rehydration in children with mild-to-moderate dehydration. These tubes should be considered to assist in the nutritional recovery of children who are critically ill or severely dehydrated.