A delta check is a quality control tool that compares laboratory test results with results obtained on previous samples from the same patient. Delta checks can be programmed into the laboratory’s computer system to detect errors. For example, in the hematology laboratory, a delta check for MCV would compare a patient's current MCV of 80 fL to their last value, obtained perhaps 12 hours ago, which was 95 fL. This significant change could indicate pathology or an issue with the testing or test sample. The lab's computer system would alert the instrument operator to this substantial change.
Delta checks are handy for detecting errors in specimen identification, integrity, manual data entry errors, or possible analytical errors. Testing QC materials usually cannot detect these quality control issues.
For most tests, consecutive results obtained on one patient are unlikely to vary significantly unless a substantial change has occurred in the patient’s medical status. Changes in patient status cause the majority of delta check failures. However, if multiple delta checks fail on several tests performed on a single patient, there is a strong possibility that the patient or specimen was misidentified.
Delta checks are not helpful for every analyte; they are best suited to stable analytes with slight day-to-day variations measured frequently, such as red blood cell (RBC) indices, electrolytes, or liver function tests.
