Two-step method of diagnostic strategy is a method to diagnose FUO disease. First step is to differentiate FUO according to the onset of disease and invasive pathogens. Second step is to further differentiate FUO according to trends of disease and inflammation scores. The diagnosis of FUO can be difficult for both patients and their physicians. Depending on the experience and qualifications of the treating physicians, time to reach a diagnosis can vary. Two-step method of diagnostic strategy would afford a standard method for physicians to diagnoses the FUO.