What is the increase in platelet count per microliter (μL) after transfusion of one unit of platelets?

Expected Platelet Increment Per Unit Transfused

One unit of whole blood-derived platelet concentrate increases the platelet count by approximately 5,000-10,000/μL in an average-sized adult, while one apheresis unit increases the count by approximately 30,000-50,000/μL. 1

Standard Expected Increments

Whole Blood-Derived Platelet Concentrates

• Each single unit increases platelet count by approximately 5,000-10,000/μL (or 5-10 × 10⁹/L) in a 70 kg adult 1
• The American Society of Clinical Oncology suggests using a rough estimate of 2,000/μL per unit as a practical approximation for average-sized adults 2, 1
• Each unit contains approximately 0.7-0.75 × 10¹¹ platelets on average 1

Apheresis Platelet Units

• One apheresis unit increases platelet count by approximately 30,000-50,000/μL (or 10,000/μL per apheresis unit as an alternative estimate) 1
• Apheresis units contain approximately 3-6 × 10¹¹ platelets, equivalent to 4-8 whole blood-derived units 1

Pediatric Dosing

• For children, the approximate equivalent calculation is 3,500/μL per m² per unit 2, 1

Calculating Expected Response Using CCI

The Corrected Count Increment (CCI) provides a standardized assessment that accounts for patient body surface area and platelet dose 2, 1:

• CCI Formula: CCI = (absolute increment × body surface area in m²) / (number of platelets transfused × 10¹¹) 2, 1
• A CCI ≥ 5,000 defines a satisfactory transfusion response 2, 1
• The absolute increment is calculated by subtracting the pre-transfusion platelet count from the count obtained 10 minutes to 1 hour post-transfusion 2

Clinical Factors That Reduce Expected Increments

Important caveat: The above estimates assume ideal conditions. Multiple factors can significantly diminish the actual platelet increment:

• Sepsis and active infection markedly reduce platelet recovery 1
• Splenomegaly reduces expected increment (approximately 33% of transfused platelets normally pool in the spleen) 1
• Disseminated intravascular coagulation (DIC) and massive hemorrhage consume transfused platelets 1
• ABO incompatibility (e.g., group A platelets to group O recipients) can compromise post-transfusion increments 2, 1, 3
• Alloimmunization (HLA antibodies present in approximately 90% of refractory cases) significantly reduces platelet recovery 2, 1
• Shock, hypersplenism, and drug-related antibodies also diminish expected increments 2

Defining Inadequate Response (Refractoriness)

Refractoriness should only be diagnosed when at least two consecutive ABO-compatible transfusions (stored <72 hours) result in poor increments, defined as:

• CCI <5,000 on both occasions, OR
• Absolute increment <2,000/μL per unit 2, 1

This two-transfusion requirement is critical because patients may have a poor increment to a single transfusion yet have adequate increments with subsequent transfusions 2

Practical Clinical Application

• For bleeding patients: A pool of 4-8 platelet concentrates or a single-donor apheresis unit is usually sufficient to provide hemostasis 1
• Post-transfusion monitoring: Obtain platelet counts 10 minutes to 1 hour after transfusion to assess adequacy 2
• ABO compatibility: Use ABO-compatible products whenever possible to optimize platelet increments 1, 3