Performance characteristics of Bull's multirule algorithm for the quality control of multichannel hematology analyzers.

The multirule quality control procedure for interpreting Bull's moving averages, proposed by Levy and colleagues (Am J Clin Pathol 1986; 85: 719-721.), has been evaluated by computer simulation with the use of the approach of Cembrowski and Westgard (Am J Clin Pathol 1985; 83: 337-345.). With this procedure, a batch of patient specimens is rejected if either of two criteria are satisfied: (1) the Bull's mean of one of the red blood cell indices is outside its 3% limits, or (2) the average of three consecutive Bull's means is outside its 2% limits. Power function curves were used to summarize the performance of the multirule approach and demonstrated error-detection capabilities that are superior to the more common implementation of Bull's algorithm using 3% limits for single Bull's means. The increased error detection achieved by the multirule procedure allows shifts in hemoglobin and mean corpuscular volume to be more readily detected but also results in the detection of small shifts in red blood cell count. A modified multirule procedure was also tested and was found to be ineffective. The authors recommend the multirule of Levy and colleagues but caution that its use may result in the detection of small shifts in the red blood cell count.

An optimized quality control procedure for hematology analyzers with the use of retained patient specimens.

The authors propose guidelines for the use of retained patient specimens for the quality control of multichannel hematology analyzers. They demonstrate that control limits for patient specimen replicates may be derived from the long-term standard deviations (s) of commercial whole blood controls. They then use computer stimulation of the Coulter multichannel hematology instrument to determine power functions of various procedures using retained specimens. These power functions show that the use of three patient specimens and +/- 2 s limits are optimal for the detection of systematic error. They recommend that three different, previously analyzed normal range specimens be periodically analyzed, e.g., at eight-hour intervals. The differences between the current and original measurements should then be calculated and compared with their +/- 2 s limits. If at least two of the three differences for any directly measured parameter exceed the +/- 2 s limits, there will be a high probability of significant analytic error. Because the power functions of the derived red blood cell parameters, hematocrit, mean corpuscular hemoglobin, and mean corpuscular hemoglobin concentration demonstrate relatively low error detection capabilities, the authors recommend that these parameters not be monitored with the retained patient specimen procedure.