Basic Equation Approach
ideal number of platelet units to give =
= ((increment wanted) * (blood volume) / (number of platelets per unit))
actual number of platelet units to give =
= ((ideal number) / (fractional yield you "expect"))
For further description of this method, see Maximal Platelet Count Increment (MPI), below.
Heuristic Approach
Rule of Thumb : Ideally, a 70 kg person with 1.8 sq meter BSA should see a 5,000-10,000/µL increase in platelet count for each unit of platelets given. This assumes that the minimum number of platelets per unit is (5.5 * 10^10).
As the blood volume increases or decreases much from the "average", the less predictable this heuristic will work.
Based on the heuristic approach:
Step 1: Decide the increment you want
Step 2: Guess how you expect the patient to respond (whoa!) to a single unit (where along the spectrum of 5,000 - 10,000 platelets/µL per unit) = "guess at increment per unit"
Step 3: [(increment wanted) / (guess at increment per unit)] = number of units to give
Annotation to heuristic:
(1) A BSA of 1.8 square meters works out to a blood volume of 4.71 liters (4.71 * 10^6 µL).
(2) If the minimum number of platelets was present in a single unit, then the increment for 1 unit of platelets should be ((5.5 * 10^10) / (4.71 * 10^6)) approximates 10,000.
(3) Since you can expect that more platelets are given than the minimum, the heuristic assumes less than ideal (ranges down to 50%) recovery.
(4) One unit of platelet concentrate usually increases the platelet count of an adult with a blood volume of 5,000 mL by about 5,000/µL (Jacobs 1994).
