Prognosis

When applied to large statistical populations, prognostic estimates can be very accurate: for example the statement "45% of patients with severe septic shock will die within 28 days" can be made with some confidence, because previous research found that this proportion of patients died. This statistical information does not apply to the prognosis for each individual patient, because patient-specific factors can substantially change the expected course of the disease: additional information is needed to determine whether a patient belongs to the 45% who will die, or to the 55% who survive.

Methodology

Disease and prognostic indicators

Prognostic scoring is also used for cancer outcome predictions. A Manchester score is an indicator of prognosis for small-cell lung cancer. For non-Hodgkin lymphoma, physicians have developed the International Prognostic Index to predict patient outcome. Other medical areas where prognostic indicators are used include drug-induced liver injury (DILI) (Hy's law), the use of an exercise stress test after myocardial infarction, and to predict survival in people with multiple myeloma.

End of life

Studies have found that most doctors are overly optimistic when making a prognosis; they tend to overstate how long a patient might live. For patients who are critically ill, particularly those in an intensive care unit, there are numerical prognostic scoring systems that are more accurate. The most famous of these is the APACHE II scale, which is most accurate when applied in the seven days prior to a patient's predicted death.

Knowing the prognosis helps determine whether it makes more sense to attempt or withhold certain treatments, and thus plays an important role in end-of-life decisions and advance care planning.