How much does 1 unit of platelets (PLTs) increase the platelet count?

Expected Platelet Increment from 1 Unit of Platelets

One unit of whole blood-derived platelet concentrate increases the platelet count by approximately 5,000-10,000/μL in an average-sized adult (70 kg, body surface area 1.76 m²). 1, 2

Standard Expected Increments by Product Type

Whole Blood-Derived Platelet Concentrate (Single Unit)

• Expected increment: 5,000-10,000/μL per unit 1, 2, 3, 4
• Each unit contains approximately 0.7-0.75 × 10¹¹ platelets 1, 2
• The American Society of Clinical Oncology recommends using 2,000/μL per unit as a rough estimate for average-sized adults 1, 2
• This estimate assumes a body surface area of 1.76 m² 1

Apheresis Platelet Unit

• Expected increment: 30,000-50,000/μL per apheresis unit 2, 3, 4
• One apheresis unit contains 3-6 × 10¹¹ platelets (equivalent to 4-8 whole blood-derived units) 2, 3, 4
• Alternative calculation: approximately 10,000/μL per apheresis unit 2

Pediatric Dosing Considerations

For children, the expected increment is approximately 3,500/m²/unit 1, which accounts for smaller body surface area and blood volume.

Assessing Transfusion Adequacy

Corrected Count Increment (CCI)

The American Society of Clinical Oncology endorses the CCI formula to standardize assessment: 1, 2

CCI = (absolute increment × body surface area in m²) / (number of platelets transfused × 10¹¹) 1, 2

• A CCI ≥ 5,000 defines a satisfactory response 1, 2
• The absolute increment is calculated by subtracting the pre-transfusion count from the post-transfusion count at 1 hour (or 10 minutes) 1

Example Calculation

If transfusion of 4 × 10¹¹ platelets produces an increment of 40,000/μL in a 2 m² recipient: 1

• CCI = 40,000 × 2 / 4 = 20,000 (satisfactory response)

Clinical Factors That Reduce Expected Increments

Common Causes of Poor Platelet Recovery

• Sepsis and active infection significantly diminish the expected increment 2
• Splenomegaly reduces increment (approximately 33% of transfused platelets pool in the spleen normally) 2
• Disseminated intravascular coagulation (DIC) and massive hemorrhage 1, 2
• Alloimmunization (HLA antibodies in approximately 90% of cases) 1, 2
• ABO incompatibility (e.g., A platelets to group O recipients) can compromise increments 1, 2

Special Clinical Scenarios

• Trauma with massive transfusion: one standard adult platelet dose may increase count by only 5-10 × 10⁹/L 2
• Cirrhosis patients: transfusion produces only a small increase in platelet count 2
• Uremia: superimposed renal failure causes platelet dysfunction and reduces increment 1

Defining Platelet Refractoriness

Refractoriness should only be diagnosed when at least two consecutive ABO-compatible transfusions (stored <72 hours) result in poor increments. 1, 2

Criteria for Refractoriness

• CCI <5,000 on both occasions 1, 2
• Absolute increment <2,000/unit 1, 2
• Patients may have a poor increment to a single transfusion yet have excellent increments with subsequent transfusions, so two failed transfusions are required for diagnosis 1

Critical Pitfalls to Avoid

• Do not diagnose refractoriness after a single poor increment – patients may respond adequately to subsequent transfusions 1, 2
• Ensure ABO compatibility – ABO-incompatible platelets can compromise post-transfusion increments 1, 2
• Check platelet storage time – platelets stored >72 hours may have reduced viability 1, 2
• Consider clinical factors – sepsis, splenomegaly, DIC, and massive hemorrhage all reduce expected increments before assuming alloimmunization 1, 2
• Monitor post-transfusion counts at 1 hour (or 10 minutes) to assess adequacy and guide further management 1