Purpose: Preanalytical phase is the most common source of laboratory errors. Preanalytical errors generally cause unsuitable samples for analysis. This study was aimed to evaluate prevalence and type of rejected samples using six sigma as well as to determine the prevalence and type of rejected samples at inpatient, outpatient, routine and stat patients.

Material and Method: The number and type of rejected samples were collected by laboratory information system from 1 January to 31 December 2015.

Results: The ratio of total rejected samples was 0.33%. The most frequent reason for the rejection was the clotted specimen (32.7%), followed by hemolyzed samples (28%) and incompatibility of blood / anticoagulant ratio (12.5%). The frequency of rejected samples was higher in inpatient than outpatients. Similarly, the frequency of rejected samples differed between routine and stat patients, being higher in stat patients. Sigma value was calculated as 4.25 for total rejected samples. When six sigma values were separately calculated according to reasons of rejection, it was found to be 4.37 to 5.87. Sigma value was lower in inpatient compared to those of outpatient. In addition, stat patients had lower sigma value than those of routine patients.

Conclusion: The frequency of rejected samples can be assessed by converting the number of rejected samples to six sigma values. The frequency of rejected samples was found acceptable according to six sigma values calculated in the present study. In addition, it was concluded that the rejected samples should be more closely monitored in inpatients and stat patients.