A diagnosis of dehydration is frequently based upon clinical signs and symptoms, and appropriate treatment is given. Laboratory testing is typically not required for mild to moderate dehydration, but a variety of non-laboratory evaluations may be used to assess an individual with more serious signs and symptoms.
These may include an evaluation of:
- Urine output and production of tears
- Examination of dryness of skin and mucous membranes
- Breathing rate – is it rapid?
- Heart rate – is it rapid?
- Blood pressure – is it low?
- Skin turgor – when a fold of skin is pinched and then released, does it bounce back in shape or only slowly relax?
- Capillary refill rate – is it slower than normal? For this evaluation, pressure is applied to a patient's nail bed until it turns white, indicating blood has been forced out. Then the pressure is released. The time that it takes for the nail bed to turn pink again, indicating return of blood, is observed.
- Do eyes appear sunken and, if so, to what degree?
- State of consciousness
In cases of severe dehydration, laboratory testing is frequently ordered to identify electrolyte and acid-base imbalances, to evaluate kidney function, and general health status. If imbalances and/or organ dysfunction are found, then serial testing may be performed to monitor the person over time and their response to treatment. Testing may include:
- Basic metabolic panel (BMP) – this panel of tests can provide information on general health as well as acid-base balance and kidney function:
- Urinalysis – both to evaluate how much urine is being produced and to examine its color and concentration
- Complete blood count (CBC) – to evaluate blood cells and the balance between the solid and liquid portions of the blood; specifically, one component, the hematocrit, can be elevated with dehydration.
- Glucose – to detect a high level that may indicate uncontrolled diabetes
- Urine and/or blood osmolality – evaluates the body's water balance
If the cause of dehydration is apparent, then usually no other testing is necessary. However, a variety of tests may be performed when the cause is unknown, to diagnose and address underlying conditions, such as those associated with prolonged diarrhea and/or vomiting.
- Stool culture – to look for bacterial infection as a cause for diarrhea
- Clostridium difficile and C. diff toxin test
- O&P – to detect intestinal parasites
A wide variety of other tests may be done depending on what is suspected to be the underlying cause of the signs and symptoms, such as: