What is the corrected count increment (CCI) cut-off for diagnosing platelet refractoriness?

Corrected Count Increment (CCI) Cut-off for Diagnosing Platelet Refractoriness

A CCI of less than 5,000 is the established cut-off for diagnosing platelet refractoriness, with diagnosis requiring at least two consecutive ABO-compatible platelet transfusions resulting in poor increments. 1

Definition and Calculation of CCI

The Corrected Count Increment (CCI) standardizes the platelet response based on patient size and the number of platelets transfused:

• Formula: CCI = (absolute increment × body surface area [m²]) / (number of platelets transfused × 10¹¹) 1, 2

• Example: If transfusion of 4 × 10¹¹ platelets produces an increment of 40,000/mL in a 2-m² recipient, the CCI = 40,000 × 2/4 = 20,000 1

Practical Approximations When Platelet Count of Product is Unknown

Since many centers don't routinely measure platelet counts in transfusion products, the following approximations are clinically useful:

• Adults: An absolute increment of 2,000/unit of platelet concentrate or 10,000/transfusion of apheresis platelets is roughly equivalent to a CCI of 5,000 1, 2

• Children: An approximate equivalent calculation is 3,500/m²/unit 1, 2

These approximations assume an average adult has a body surface area of 1.76 m² and the average platelet count in a unit of platelet concentrate is 0.7 × 10¹¹ 1

Timing of Post-Transfusion Assessment

• Platelet counts should be performed 10-60 minutes after transfusion 2
• The 10-minute timepoint is particularly practical as the patient must be seen when the transfusion is completed to switch IV bags 1
• A 1-hour post-transfusion count provides identical results to the 10-minute count 1

Diagnosing Platelet Refractoriness

Refractoriness should only be diagnosed when:

1. At least two ABO-compatible platelet transfusions result in poor increments (CCI < 5,000) 1, 2
2. The platelets used were stored for less than 72 hours 1

This requirement exists because patients may have a poor increment to a single transfusion yet have adequate increments with subsequent transfusions 1

Clinical Significance and Management

• In the PLADO trial, 14% of patients (102 of 734) demonstrated platelet refractoriness by this definition 3
• Alloimmunization was detected in only 8% of refractory cases, indicating that non-immune causes are more common 3
• Patients with alloimmune refractory thrombocytopenia are best managed with HLA-A and HLA-B matched platelet transfusions 1
• For patients who don't respond to HLA-matched platelets, platelet cross-matching techniques can identify compatible donors 1

Causes of Refractoriness

Refractoriness may be due to:

• Immune causes:

  • HLA alloimmunization (most common immune cause, ~90% of alloimmunized patients) 1
  • Platelet-specific antibodies 1
  • Drug-related antibodies 1

• Non-immune causes:

  • Splenomegaly (significant influence on refractoriness) 4, 5
  • Anti-platelet drugs (significant influence) 4
  • Fever, bleeding, sepsis, DIC (more common in refractory patients but not statistically significant in some studies) 4

Clinical Pitfalls to Avoid

• Failing to use ABO-compatible platelets when assessing for refractoriness (ABO incompatibility can compromise post-transfusion increments) 1
• Diagnosing refractoriness based on a single poor increment 1
• Not calculating CCI, which can lead to misinterpretation of transfusion adequacy 2
• Assuming a hemostatic blood count has been achieved simply because a transfusion was administered without confirming with post-transfusion counts 2

By consistently using the CCI < 5,000 threshold across two consecutive transfusions, clinicians can accurately identify patients with true platelet refractoriness and initiate appropriate management strategies to reduce morbidity and mortality from bleeding complications.