According to the U.S. Centers for Medicare and Medicaid Services, there is only one ICD-9 code for dehydration. CMS reports that code 276.51 specifies dehydration.
The American College of Emergency Physicians indicates that the ICD-9 code for dehydration is the International Classification of Diseases (ninth edition) code to denote a diagnosis of dehydration. The code is used for the purpose of medical records and billing.
MedlinePlus defines dehydration as the body not having as much water and fluid as it should. Dehydration ranges from mild to moderate to severe. Severe dehydration is life-threatening, and immediate medical attention is required to treat it.