Tests
1st tests to order
clinical diagnosis
Test
Patients presenting with mild to moderate volume depletion do not require specific tests beyond a careful history and physical exam.
Patients who present with inconsistent history, severe volume depletion, or who do not respond to initial fluid resuscitation are a small subset of patients in whom diagnostic testing should be considered.
Use of a clinical scale or scoring system may improve diagnostic accuracy.[17]
Result
clinical findings vary by age and specific etiology but can include generalized irritability, decreased activity, tachycardia, delayed capillary refill, dry mucous membranes, sunken eyes, decreased skin turgor, and decreased urination
Tests to consider
serum electrolytes
Test
Differentiating hypernatremic, isonatremic, and hyponatremic volume losses helps guide subsequent therapy.
Serum bicarbonate is low in many types of hypovolemia due to direct losses as in diarrhea or poor tissue perfusion from decreased intravascular volume.
BUN/Cr is >20:1 with renal hypoperfusion.
Serum potassium is low in enteral losses but can be high in crush injuries and burns.
Result
may show hypernatremia, isonatremia, or hyponatremia; enteral losses: associated with hypokalemia and low bicarbonate level; crush injuries and burns: may be associated with hyperkalemia
blood glucose
Test
Young children are at risk for hypoglycemia with any significant illness. This must be recognized and treated promptly. Hyperglycemia occurs in diabetic ketoacidosis.
Rapid bedside testing is a readily available, quick, and appropriate initial screen, but should be confirmed with serum glucose to rule out false elevation that may mask hypoglycemia.
Result
may show hypo- or hyperglycemia
BUN/Cr
Test
Prerenal azotemia frequently accompanies volume depletion.
Result
renal hypoperfusion: >20:1
CBC
Test
Anemia can be seen in nonacute blood loss. Hemoconcentration may be noted in the setting of loss of plasma volume, especially burns.
Leukocytosis or neutropenia is common in the setting of infection. In acute hemorrhage, whole blood is lost and, until plasma volume is expanded by fluids, hematocrit is likely to be normal.
Result
hemoglobin and hematocrit: may be decreased, normal, or increased; abnormal WBC count with predominance of neutrophils or immature band forms
urinalysis
Test
Urine should be examined for signs of urosepsis and ketonuria.
Result
diabetic ketoacidosis: glycosuria, ketonuria; renal dysfunction: proteinuria; urosepsis: may be proteinuria, hematuria
urine specific gravity
Test
Concentration of urine leading to a high urine osmolarity is an appropriate physiologic response to volume depletion, but may not reliably predict dehydration.[17][25]
Infants <6 months old are less able to concentrate urine due to renal immaturity, and they may not have a high specific gravity.
Hypovolemic children with normally functioning kidneys have elevated specific gravity.
In conditions of abnormal renal function, urine specific gravity is normal or inappropriately low.
Result
normally functioning kidneys: >1.025; abnormally functioning kidneys: normal or inappropriately low
urine osmolality
Test
Concentration of urine leading to a high urine osmolarity is an appropriate physiologic response to volume depletion.
Patients with primary renal losses have inappropriately dilute urine in the face of significant volume depletion.
Result
usually >450 mOsm/kg
urine microscopy and culture
Test
Performed if sepsis suspected.
Result
sepsis: WBCs and pathogens may be seen on microscopy in urinary infection; culture may demonstrate specific infective pathogen
blood culture
Test
Performed if sepsis suspected.
Result
sepsis: may demonstrate specific infective pathogen
ABG
Test
Disorders of acid-base balance are frequently seen in the setting of volume depletion (e.g., lactic acidosis, DKA).
Result
may be evidence of metabolic acidosis
head ultrasound or CT scan
Test
Blunt trauma, especially to the head and abdominal viscera, can be a major cause of hemorrhage-associated volume depletion. Altered mental status in a child known to have sustained trauma or in a young infant should prompt investigation for occult bleeding.
History is often hidden in settings of abuse.
Result
trauma: may demonstrate intracranial bleed
abdominal ultrasound or CT scan
Test
Blunt trauma, especially to the head and abdominal viscera, is a major cause of hemorrhage-associated volume depletion. Altered mental status in a child known to have sustained trauma or in a young infant should prompt an investigation for occult bleeding.
History is often hidden in settings of abuse.
Result
trauma: may demonstrate intra-abdominal bleed
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