Medical Sign - Signs As Tests

Signs As Tests

In some senses, the process of diagnosis is always a matter of assessing the likelihood that a given condition is present in the patient. In a patient who presents with haemoptysis (coughing up blood), the haemoptysis is very much more likely to be caused by respiratory disease than by the patient having broken their toe. Each question in the history taking allows the medical practitioner to narrow down their view of the cause of the symptom, testing and building up their hypotheses as they go along.

Examination, which is essentially looking for clinical signs, allows the medical practitioner to see if there is evidence in the patient's body to support their hypotheses about the disease that might be present.

A patient who has given a good story to support a diagnosis of tuberculosis might be found, on examination, to show signs that lead the practitioner away from that diagnosis and more towards sarcoidosis, for example. Examination for signs tests the practitioner's hypotheses, and each time a sign is found that supports a given diagnosis, that diagnosis becomes more likely.

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. The x-ray film shows a fractured tibia, so the film is said to be diagnostic of the fracture.