This section includes symptoms, signs, abnormal results of laboratory or other investigative procedures, and ill-defined conditions regarding which no diagnosis classifiable elsewhere is recorded.

Signs and symptoms that point rather definitely to a given diagnosis are assigned to some category in the preceding part of the classification. In general, categories 780-796 include the more ill-defined conditions and symptoms that point with perhaps equal suspicion to two or more diseases or to two or more systems of the body, and without the necessary study of the case to make a final diagnosis. Practically all categories in this group could be designated as "not otherwise specified," or as "unknown etiology," or as "transient." The Alphabetic Index should be consulted to determine which symptoms and signs are to be allocated here and which to more specific sections of the classification; the residual subcategories numbered .9 are provided for other relevant symptoms which cannot be allocated elsewhere in the classification.

The conditions and signs or symptoms included in categories 780-796 consist of: (a) cases for which no more specific diagnosis can be made even after all facts bearing on the case have been investigated; (b) signs or symptoms existing at the time of initial encounter that proved to be transient and whose causes could not be determined; (c) provisional diagnoses in a patient who failed to return for further investigation or care; (d) cases referred elsewhere for investigation or treatment before the diagnosis was made; (e) cases in which a more precise diagnosis was not available for any other reason; (f) certain symptoms which represent important problems in medical care and which it might be desired to classify in addition to a known cause.

This classification is provided to deal with occasions when circumstances other than a disease or injury classifiable to categories 001-999 (the main part of ICD) are recorded as "diagnoses" or "problems." This can arise mainly in three ways:

a) When a person who is not currently sick encounters the health services for some specific purpose, such as to act as a donor of an organ or tissue, to receive prophylactic vaccination, or to discuss a problem which is in itself not a disease or injury. This will be a fairly rare occurrence among hospital inpatients, but will be relatively more common among hospital outpatients and patients of family practitioners, health clinics, etc.

b) When a person with a known disease or injury, whether it is current or resolving, encounters the health care system for a specific treatment of that disease or injury (e.g., dialysis for renal disease; chemotherapy for malignancy; cast change).

c) When some circumstance or problem is present which influences the person's health status but is not in itself a current illness or injury. Such factors may be elicited during population surveys, when the person may or may not be currently sick, or be recorded as an additional factor to be borne in mind when the person is receiving care for some current illness or injury classifiable to categories 001-999.

In the latter circumstances the V code should be used only as a supplementary code and should not be the one selected for use in primary, single cause tabulations. Examples of these circumstances are a personal history of certain diseases, or a person with an artificial heart valve in situ.