Alaska Subscriber
Answer: For generalized weakness only, you should assign 780.79 (Other malaise and fatigue). Code 780.79 is for a "nonspecific" diagnosis, and you should report it only if the physician can identify no other, more specific symptoms. Payers prefer definitive diagnoses and may reject your claim for lack of medical necessity, especially if you link the diagnosis to a higher-level E/M service or other costly procedure.
Before reporting 780.79, or any other "unspecified" ICD-9 code, check with the treating physician to be sure that he cannot provide a more precise diagnosis.