Steps:
(1) Record the number of each ABO and Rh type transfused each week for 26 weeks (A positive, A negative, B positive, B negative, AB positive, AB negative, O positive, O negative).
(2) Sum the usage for each type over the 26 weeks.
(3) Subtract the maximum weekly value for each type from its total sum. This is intended to reduce the impact of any unexpected heavy use that might skew the results.
(4) Divide the reduced sum by 25 to get the average weekly use for each type. The denominator of 25 is based on 26 minus 1 for maximum usage of the type.
Limitations:
(1) Requires data collection over 6 months.
(2) Provides a reasonable estimate if blood usage is constant. A change that significantly increases or decreases use may require recalculation.
(3) Other considerations such as delivery time from the blood center will determine how low the inventory can be kept.
