In meicine, differential diagnosis (sometimes abbreviated DDx, ddx, or ΔΔ) is the systematic method healthcare providers use to identify the disease causing a patient's symptoms. In other words, part of diagnosis is attempting to narrow down the list of possible diagnoses until one emerges as the best. The term differential evolves from the word differences. The concept of differential diagnosis involves observing and discovering signs and symptoms, then progressively considering the most likely illnesses, then continuously narrowing down the possible diagnoses, eliminating one after another, until one is left with only one specific diagnosis for the patient's signs and symptoms.