[Do chronic diseases prevent intra-hospital mortality? Paradoxes and biases in information about hospital morbidity].

OBJECTIVE: Previous studies have demonstrated how the incomplete codification of the secondary diagnostics can bias the estimation of the risk of in-hospital death based on clinical-administrative databases. The objective of this study is to measure the trend of the association between in-hospital mortality and the secondary diagnostics register in the Minimum Basic Data Set (MBDS) of the Valencian Community.
METHODS: The 14,161 admissions of persons over the age of 64 were extracted from the MBDS (years 1993-94) for: stroke (S), bacterial pneumonia (BN), myocardial infarction (MI) and congestive heart failure (CHF). The relation was measured between the availability of some additional diagnostics (selected to dispose of a group of heterogeneous chronic and acute processes), and the risk of in-hospital death, relative risk (RR) and adjusted odds ratios (aOR) were calculated per age, gender, length of stay and number of diagnoses.
RESULTS: Many of the conditions are associated with a reduced risk of death such as the diabetes mellitus (Mortality for stroke, RR: 0.58; aOR: 0.53), old myocardial infarction (mortality for myocardial infarction, RR: 0.40; aOR: 0.35) or hypertension (mortality for stroke, RR: 0.54; aOR: 0.49): this also occurs in angina, coronary atherosclerosis, aortic and mitral valve disease, atrial fibrillation, chronic obstructive pulmonary disease and urinary tract infection.
CONCLUSIONS: Although there maybe other explanations, such as the existence of a bias in the hospital selection, the explanation which is most in agreement with the findings is the presence of an information bias in the MBDS due to the tendency to register less information about chronic antecedents of the persons who die.