Abstract: Objective To analyze the occurrence and the related causes of the invalid Results in Roche Cobas s201 nucleic acid detection systems （NAT） for blood screening．Methods The number and types of invalid Results in NAT from January 2015 to December 2017 were identified and calculated. The relationship among the result invalidation and detection time and the reagent lots etc were analyzed. Results Among 21 032 pools （94 397） tested by Roche Cobas s201, 55 invalid pools were found. The total rate of result invalidation in the lab was 0. 26% （55 /21 032）. From 2015 to 2017, the rates of result invalidation were 0.35% （25/7 055）, 0.29% （20/6 785）and 0.14% （10/7 192）, respectively. There were significant differences in different years （χ²=6. 755,P<0. 05）. The rate of result invalidation in the lab was decreasing with trend test （trend for χ² was 6.334 8, P=0.012）.The causes were mainly due to spotting failure or clot or air bubble in samples 61.82%（34/55）, There were significant differences compared with other invalid Results （χ²=6.145,P=0. 013）. There were significant differences among the invalid Results of different years, χ²=25.485, P=0.004.. There were no significant differences in the rates of the result invalidation in different months （P>0. 05）. The rates of the result invalidation were the highest in reagent Lot 5. It was 1. 22% （4 /329）. There were significant differences in the rates of the result invalidation among different reagent lots （χ² =10 342.525,P<0. 001）. Conclusion The invalidation rate of NAT in the lab was in normal and decreasing year by year. There was some correlation between different reagent lots and result invalidation. Monitoring the invalid rates of NAT Results can help to monitor the nucleic acid test performance continuously．

Key words: Blood screening, Nucleic acid detection, Cobas s201, Rate of the result invalidation, Analysis