Background and aim:Blood cells have an important role in human healthy, so their shapes and numbers are defined as human healthy indexes. These factors are measured by cell counter machines. Presenting a high quality report according to cell counters output is dependant on their operational accuracy. Therefore it was necessary to do a study on quality control of blood cell counter machines in selective medical laboratories of Tehran.

Method of study:This study was an experimental type in selective medical laboratories of Tehran. "Brittin method" was used as a general method for 6 selective machines over WBC, RBC, Hb, HCT, MCV, MCH and MCHC. In this method red blood cells index stability with EDTA, in 4^oC for 24 hour is assessed. Data was collected before and after quality controls and finally data analysis was done by T- student (paired samples T test) method and SPSS software.

Results:Using Brittin method showed all selective machines had significant differences before and after quality control in one or more quality factors (P-value< 0.05).

Conclusion:Quality control can show inaccuracy in cell counter machines output and finally inaccuracy over patient blood tests. By this subject we can have high quality diagnosis. This study showed parameters producing errors are error in sample volume, biological factors, error in concentration and using bad solutions.