Diagnosing dehydration often begins with a medical history. A physician may ask questions about any recent illnesses, conditions or activities that may increase the risk of dehydration. A physical examination is also performed, which may include taking the patient’s temperature, blood pressure, heart rate, and examining the condition of the patient’s skin.

Certain tests may be performed to confirm a diagnosis of dehydration, including:

• Urine test. A urine sample is analyzed in a laboratory to identify whether dehydration exists and whether it is mild, moderate or severe. This is done by checking urine color, clarity and whether certain carbon compounds are present. The volume of water in urine, specific gravity, may also be determined.
  
  
• Blood test. Blood is drawn to identify electrolyte (e.g., sodium, potassium) and blood concentration levels in the body, both of which may indicate a fluid imbalance. Blood tests may also be used to evaluate kidney function, which can affect urine output.