A physician is likely to take a medical history and conduct a physical examination before making a diagnosis. In diagnosing dehydration, a physician will look for:

• Low blood pressure (hypotension)
• Dryness of mouth and lips
• Rapid heart rate (tachycardia)
• Delayed refilling of the capillaries
• Shock

Blood tests and urine tests may help confirm a diagnosis of dehydration. Tests that are often used to diagnose dehydration include:

• Blood chemistries. These can check levels of electrolytes (particularly sodium and potassium) and bicarbonate.
  
  
• Urine specific gravity. This measures the specific gravity of urine, a reflection of the concentration of particles in urine. A high specific gravity indicates substantial dehydration.
  
  
• Blood urea nitrogen (BUN) test. This waste product test measures the amount of a byproduct of protein metabolism.
  
  
• Creatinine test. Elevated readings of the muscle constituent creatine may indicate dehydration.
  
  
• Complete blood count (CBC). Signs of concentrated blood (hemoconcentration) indicate dehydration.