There are a number of rules for the formulation of clinical diagnosis for comorbid patients, which must be followed by a practitioner. The main principle is to distinguish in diagnosis the primary and background diseases, as well as their complications and accompanying pathologies. * Primary disease: This is the nosological form, which itself or as a result of complications calls for the foremost necessity for treatment at the time due to threat to the patient's life and danger of disability. Primary is the disease, which becomes the cause of seeking medical help or the reason for the patient's death. If the patient has several primary diseases it is important to first of all understand the combined primary diseases (rival or concomitant). * Rival diseases: These are the concurrent nosological forms in a patient, interdependent in etiologies and pathogenesis, but equally sharing the criterion of a primary disease (for example, transmural myocardial infarction and massive thromboembolism of pulmonary artery, caused by phlebemphraxis of lower limbs). For practicing pathologist rival are two or more diseases, exhibited in a single patient, each of which by itself or through its complications could cause the patient's death. * Polypathia: Diseases with different etiologies and pathogenesis, each of which separately could not cause death, but, concurring during development and reciprocally exacerbating each other, they cause the patient's death (for example, osteoporotic fracture of the surgical neck of the femur and hypostatic pneumonia). * Background disease: This helps in the occurrence of or adverse development of the primary disease increases its dangers and helps in the development of complications. This disease as well as the primary one requires immediate treatment (for example, type 2 diabetes). * Complications: Nosologies having pathogenetic relation to the primary disease, supporting the adverse progression of the disorder, causing acute worsening of the patient's conditions (are a part of the complicated<unk> . In a number of cases the complications of the primary disease and related to it etiological and pathogenetic factors, are indicated as conjugated disease. In this case they must be identified as the cause of<unk> . Complications are listed in a descending order of prognostic or disabling significance. * Associating diseases: Nosological units not connected etiologically and pathogenetically with the primary disease (Listed in the order of significance).
Comorbidity
Premorbidity
Multimorbidity
SAMPLE history
Family history 
Risk factor
Psychiatric history
Functional symptom