Introduction The aim of this study was to evaluate the long-term effects of the implementation of “good laboratory test practices” pro-cedure on blood test prescription, cost cutting laboratory test and patient outcome and red cells transfusion needs. In addition, we looked for factors associated with transfusion.Patients and methods This is a retrospective, single-center study.Considering that prescription of laboratory tests was excessive in our ICU, we developed in 2009 a procedure aiming at limiting assays and blood sampling. All adult patients over 18 years admitted in the ICU from January 1, 2008, to December 31, 2012, were consecutively included. For each patient, the following data were retrospectively obtained from medical records and institutional databases: demo-graphic and severity of illness parameters, the amount and costs of laboratory tests, daily blood volume drawn, number of red cells trans-fusions and ICU and in-hospital outcomes.Results A total of 3568 patients were included between January 1, 2008, and December 31, 2012. Patient’s characteristics were similar during the study with respect to overall severity and vital organ sup-port, except the need for vasoactive drugs which increased across time. After implementation of guidelines, the total number of labora-tory tests decreased from 78,406 in 2008 (18.1 tests/patient/day) to 27,514 in 2012 (6.4 tests/patient/day). 318,000€ were saved in 2012 on the five more expensive tests as compared to 2008. Average daily blood drawn volume decreased from 29.2 ± 13 ml/day in 2008 to 22.4 ± 10.1 ml/day (p < 0.001) in 2012 in the whole population. The decline was larger for transfused patients (33.8 ± 15.6 ml/day in 2008 to 23.6 ± 10.7 ml/day in 2012 p < 0.001). We observed a nonsignifi-cant reduction in PRBC administered after the institution of guidelines. Hemoglobin threshold for blood transfusion remained unchanged over time. There was a significant relationship between daily blood volume loss and blood transfusion [OR 1.012 per ml volume drawn CI (1.009–1.014), p < 0.001], but mechanical ventilation, renal replace-ment, invasive monitoring and use of vasoactive drugs were more potent independent factors for transfusion. ICU and in-hospital mor-tality did not change across time (p= 0.367 and p= 0.361)Conclusion Guidelines of laboratory tests prescription led to a sus-tained reduction in the number of laboratory tests and related costs, the average daily blood volume drawn, without changing the ICU and in-hospital mortality. Although there was a correlation between the amount of blood sampled and the transfusion of PRBC, the number of patients transfused and the amount of red blood cells transfused did not significantly decrease.