Background: Most patients hospitalized at intensive care units have a continuous infusion catheter in place for receiving drugs and solutions; nonetheless, blood sampling in these units is still performed through an invasive and painful venipuncture. However, it is possible to take blood from a peripheral venous catheter to obtain accurate laboratory test results and alleviate the suffering of patients. Objectives: The aim of this study was to compare hematology, chemistry, and blood gas values sampled from venipuncture and continuous infusion intravenous catheter. Methods: In this cross-sectional comparative study, a convenient sample of 61 adult patients was drawn according to the inclusion and exclusion criteria, from the intensive care unit. Two blood samples, one from a continuous infusion catheter, which was already in place and one from venipuncture at the other extremity, were obtained from each patient. The two sets of samples were compared in terms of hematology, biochemistry and blood gas values by using the paired-samples t-test. Results: The two sets of samples differed significantly in terms of blood sugar values. Other differences between the two sets were not statistically significant. Conclusions: Except for blood sugar, blood sampling from a continuous 24-hour infusion catheter produces reliable hematology, biochemistry and blood gas results as that of venipuncture blood sampling method. Moreover, compared with the routine venipuncture method, sampling from a continuous infusion catheter is simpler, easier and safer.