Corrected Count Increment (CCI) for platelets:

CCI = (platelet increment per ul) x (body surface area in m2)/number of platelets transfused (x 1011)

Assume each unit of random donor platelets contains 5.5 x 1010 platelets, so that a 5-pack contains 2.75 x 1011

Assume a single donor platelet pack contains 3 x 1011 platelets

For example, a platelet increment of 20,000/ul in a person of 1.8 m2 after a single donor platelet pack would represent a CCI of (20,000 x 1.8/3) = 12,000.

The expected CCI 10-60 minutes after a platelet transfusion is 7500 or greater, representing 20-30% platelet recovery.  It is best if one of these is fresh, since fresh platelets (<48 hours) sometimes survive considerably better in sick patients.   Platelet refractoriness is defined as a CCI less than 7500 for at least two sequential platelet transfusions.  When immune platelet refractoriness is suspected on the basis of poor CCI's, the next steps are to order a screen for anti-HLA antibodies and, if positive, use HLA-selected platelets.

A "quick and dirty" method for estimating platelet refractoriness assumes that the normal increment in platelet count after transfusion of 1 U/10kg platelets is 50,000 at 10-60 min and 40,000 at 18-24 h.  A one hour count less than 30% of expected, or a 24 hour count less than 20% of expected, represents an inadequate response to transfusion.

Non-immune causes of low CCIs include fever, infection, bleeding, splenomegaly, gamma-irradiation, DIC, extensive surgery, and concurrent amphotericin B therapy.  Non-immune platelet consumption is the most likely cause of a low CCI when no alloantibody can be found by the laboratory and the patient has been transfused for less than three weeks (unless there has been prior exposure to HLA antigens by transfusion, organ transplantation or pregnancy).

Reference:  Delaflor-Weiss E, Mintz PD.  The evaluation and management of platelet refractoriness and alloimmunization.  Transfus Med Rev 2000;14:180-96

Reviewed June 2015