title: Effect of drug-test interactions on length of hospital stay.
abstract: OBJECTIVE
  To evaluate the impact of drug-laboratory test interactions on the length of stay of hospitalised patients.
  
  
  METHODS
  Observational study of 404 discharges from the Internal Medicine Services of a tertiary hospital. Databases with information on general data, medication and tests performed were linked with the potential interactions described in the literature. This revealed the potential interactions between drugs and laboratory tests (PIDL) in each patient. Several linear regression models, adjusted for confounders, were performed to test the effect of both the number of PIDL and their influence on tests results (false positive/negative) on the length of stay.
  
  
  RESULTS
  A total of 19 741 PIDL were detected; 5954 could give rise to potential false positive (PFP) results and 8442 to potential false negative (PFN) ones. Each PFP was related to an increase of 0.051 days in stay duration (CI95% 0.001-0.102) and each PFN to 0.045 days (CI95% 0.008-0.081). Globally, 303 and 380 days of hospitalisation could be attributed to false positives and false negatives, which could account for 9.8% of the total stay of these patients.
  
  
  CONCLUSIONS
  These results show that the interactions between drugs and laboratory tests produce a statistically and clinically significant increase in the duration of hospital stay.
authors.affiliation: Hospital Clínico San Carlos, Clinical Pharmacology Service, Madrid, Spain.
authors.forename: Ana
authors.initials: A
authors.lastname: Terleira
authors.forename: Antonio
authors.initials: A
authors.lastname: Portolés
authors.forename: Aurora
authors.initials: A
authors.lastname: Rojas
authors.forename: Emilio
authors.initials: E
authors.lastname: Vargas
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019411:Clinical Laboratory Techniques / Q000592:standards / Q000706:statistics & numerical data; D016208:Databases, Factual / Q000706:statistics & numerical data; D004347:Drug Interactions; D005260:Female; D006801:Humans; D007902:Length of Stay / Q000706:statistics & numerical data*; D016014:Linear Models; D008297:Male; D008500:Medical Records Department, Hospital / Q000706:statistics & numerical data; D015233:Models, Statistical; D010351:Patient Discharge / Q000706:statistics & numerical data