Other health conditions can cause the same symptoms as leukemia. See your doctor if you have:
Special tests (blood tests, radiology , scans, a biopsy , etc.) also allow a hypothesis to be tested. These special tests are also said to show signs in a clinical sense. Again, a test can be considered pathognonomic for a given disease, but in that case the test is generally said to be "diagnostic" of that disease rather than pathognonomic. An example would be a history of a fall from a height, followed by a lot of pain in the leg. The signs (a swollen, tender, distorted lower leg) are only very strongly suggestive of a fracture; it might not actually be broken, and even if it is, the particular kind of fracture and its degree of dislocation need to be known, so the practitioner orders an x-ray — and, for example, if the x-ray were to show a fractured tibia , the film would be diagnostic of the fracture.