Each laboratory must establish appropriate delta check triggering limits for the normal patient population. This can be done by analyzing pairs of data points from a representative population. After evaluating the population, appropriate limits, 95 or 99%, can then be selected. Published data on diurnal variability may also be used. Once initially established, these limits may be modified.
The use of MCV to detect specimen mix-ups or incorrect patient identification is easily executed with the assistance of instrument flags. For example, if a CBC is ordered on a patient and it produces an MCV result of 90 fL, then another CBC is ordered on that patient 12 hours later, and the MCV is 79 fL, the result should be investigated before reporting the second CBC. There is a possibility that one of the samples was mislabeled and that the two tubes were not from the same patient.
MCHC is likely to be affected by hemolysis with hemoglobinemia, while the MCV will remain stable. However, the effect of hemolysis on the MCHC may be incorporated as a quality indicator for detecting sample hemolysis that occurs during collection or handling. Delta checks incorporating MCHC may have the added benefit of helping to detect analyzer malfunction. The MCHC is calculated from hemoglobin and hematocrit levels. Any malfunction in any elements incorporated into this calculation will affect the MCHC.
