Background: Mutational analysis is important in management of patients with CML. We compared BCR-ABL test results in patients who were tested for mutation after showing poor response to treatment vs. those who were not tested, to determine if mutation testing is associated with improved treatment response. Methods: We studied data from 40,000 CML patients in the Medivo Lab Value Exchange Database who were tested for BCR-ABL between 2011- 2014, and identified 6,247 instances where CML patients demonstrated a + slope in test results (defined: any subsequent test result > previous test result). We used + slope as a proxy for poor treatment response. The average time difference between two consecutive tests was 123 days. We found 183 instances (3%) where patients were tested for BCR-ABL mutation soon after showing poor treatment response, and 6,064 instances (97%) where patients were not tested. Logistic regression was used to assess whether patients who were tested for mutation were more likely to show improvement in later BCR-ABL test results than patients who were not tested. Results: Out of 183 instances where patients were tested for mutation, in 149 instances, patients showed improvement (81%) and in 34 instances, patients showed no improvement (19%). Out of 6,064 instances where patients were not tested for mutation, in 4,504 instances, patients showed improvement (74%) and in 1,560 instances, patients showed no improvement (26%). Logistic regression analysis showed that testing for BCR-ABL mutation was associated with a higher likelihood (52%) of subsequent improvement in BCR-ABL test values than not being tested for mutation, a statistically significant result (OR = 1.52, p = 0.03). Conclusions: Our results support mutation testing in patients with CML showing poor response to treatment. Further analyses are needed to confirm that patient tested for mutation are more likely to have changes in therapy and potentially better patient outcomes. Further analyses will also look at treatment choices, duration of treatment, and time to achieve MMR in these patient populations.