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Platelet refractoriness, FNAIT and neutrophil antigens

16 min

Skills you'll build4 skills
  • Calculate a corrected count increment with the stated platelet-dose units
  • Choose the next investigation for repeated poor platelet increments
  • Match maternal platelet antibodies to paternal platelet antigens in suspected FNAIT
  • Match HNA antibodies to HNA antigens in neonatal neutropenia and TRALI workups

At the bench: Check component identity, storage, and suitability before issue

Try first

Try first

A patient's platelet count rises from 6,000/µL to 18,000/µL on a count drawn 20 minutes after a transfusion of 3.8 × 10¹¹ platelets. The body surface area is 1.9 m². What is the corrected count increment (CCI)?

Keep going to see the reasoning.

Right. Keep going to follow the reasoning.

Keep going to see the reasoning.

Keep going to see the reasoning.

Keep going to see the reasoning.

Get the idea

Use the explanation to check your first decision.

The corrected count increment

CCI = (posttransfusion platelet count − pretransfusion platelet count, in platelets/µL) × body surface area (m²) ÷ platelet dose (number of 10¹¹ platelets). A dose of 3 × 10¹¹ platelets enters as 3, and refractoriness is assessed on counts drawn 10 to 60 minutes after transfusion. Keep both counts in platelets/µL. In a patient without fever or bleeding, a CCI above 7,500 on a count drawn 10 to 60 minutes after transfusion is the usual response. A CCI below 5,000 with supporting antibody results may point to immune refractoriness.1,2

Refractoriness

Refractoriness is a repeated poor response to platelet transfusion. A single low increment does not establish it. Bleeding, fever, sepsis, disseminated intravascular coagulation and an enlarged spleen cause most poor increments. It is documented by low CCIs on timed counts after two consecutive transfusions.1,2 When low increments persist after those causes are assessed, the laboratory tests for HLA class I and human platelet antigen (HPA) antibodies and obtains the patient's HLA type. Platelets are then chosen by crossmatch, by HLA match, or by avoiding the antigens the antibodies recognize.2

Antibody and antigen investigations

Three investigations follow the same approach. Identify the antibody, then show that the injured cells carry the antigen it targets.

InvestigationAntibody fromAntigen on
Fetal and neonatal alloimmune thrombocytopenia (FNAIT)The motherThe fetus's platelets, inherited from the father
Alloimmune neonatal neutropeniaThe motherThe infant's neutrophils, inherited from the father
Immune TRALIThe donorThe recipient's white cells

In FNAIT, anti-HPA-1a causes about 75% to 80% of cases in people of European ancestry.5 A routine panel detects antibodies only to the antigens on its cells. A crossmatch of the mother's serum with the father's platelets can detect an antibody to a rare paternal antigen. When the first testing is negative and clinical suspicion remains high, the reference laboratory retests 2 to 8 weeks after delivery.4,5

Human neutrophil antigen (HNA) testing needs fresh granulocytes, usually within 24 hours, at a specialized laboratory. The granulocyte immunofluorescence test (GIFT) and the granulocyte agglutination test (GAT) are used together. GIFT alone can miss anti-HNA-3a, the antibody linked to severe transfusion-related acute lung injury (TRALI).3 TRALI is classified from the clinical findings. A donor antibody that matches a recipient antigen supports the immune mechanism and guides the donor evaluation.6

Follow the bench demonstration

Sources for this step
References
  1. Association for the Advancement of Blood & Biotherapies, American Red Cross, America's Blood Centers, Armed Services Blood Program. Circular of Information for the Use of Human Blood and Blood Components. June 2024. Accessed September 27, 2026.
  2. Cohn CS. Platelet transfusion refractoriness: how do I diagnose and manage? Hematology Am Soc Hematol Educ Program. 2020;2020(1):527-532. doi:10.1182/hematology.2020000137
  3. Joint United Kingdom (UK) Blood Transfusion and Tissue Transplantation Services Professional Advisory Committee. Chapter 17: granulocyte immunology. Guidelines for the Blood Transfusion Services in the United Kingdom. Accessed September 27, 2026.
  4. Petermann R, Bakchoul T, Curtis BR, Mullier F, Miyata S, Arnold DM; Subcommittee on Platelet Immunology. Investigations for fetal and neonatal alloimmune thrombocytopenia: communication from the SSC of the ISTH. J Thromb Haemost. 2018;16(12):2526-2529. doi:10.1111/jth.14294
  5. Sachs UJ, Bedei I, Wienzek-Lischka S, et al. Diagnosis and management of fetal and neonatal alloimmune thrombocytopenia: an update 2025. Transfus Med Hemother. 2025;52(5):318-333. doi:10.1159/000547985 Accessed September 27, 2026.
  6. Vlaar APJ, Toy P, Fung M, et al. A consensus redefinition of transfusion-related acute lung injury. Transfusion. 2019;59(7):2465-2476. doi:10.1111/trf.15311

Watch one

Read each decision and its explanation.

Omar Rackham, 47 (MRN 2951406), is in induction therapy for acute myeloid leukemia. His body surface area is 1.9 m². He has no fever, no bleeding, no sign of disseminated intravascular coagulation and no enlarged spleen on record. He receives apheresis platelets on two days in a row.

  • Transfusion 1: 3.2 × 10¹¹ platelets. Count 5,000/µL before, 9,000/µL 30 minutes after.
  • Transfusion 2: 3.6 × 10¹¹ platelets. Count 6,000/µL before, 10,000/µL 45 minutes after.

Do his results indicate antibody testing?

  1. Check the draw times: 30 and 45 minutes, both inside the window.

    Only a count drawn 10 to 60 minutes after the transfusion shows whether the transfused platelets survived in circulation.

  2. CCI 1 = (9,000 − 5,000) × 1.9 ÷ 3.2 = 2,375.

    The CCI adjusts the rise for his size and for the dose he received.

  3. CCI 2 = (10,000 − 6,000) × 1.9 ÷ 3.6 = 2,111.

    Refractoriness needs a repeated poor response, so the CCI for the second transfusion is calculated the same way.

  4. Review the nonimmune causes. None is recorded.

    Nonimmune causes explain most poor increments and are assessed before antibody testing.

  5. Send HLA class I and HPA antibody testing, and obtain his HLA type.

    Two timed CCIs below 5,000 with no nonimmune cause fit immune refractoriness, and the antibody results guide platelet selection.

Yes. His CCIs of about 2,400 and 2,100 on timed counts after two transfusions in a row, with no nonimmune cause, fit refractoriness. The next steps are HLA class I and HPA antibody testing and his HLA type, and the results guide crossmatch-compatible or HLA-selected platelets.

Practice this skill

Your turn

Problem 1 of 3 · Hints available

Platelets rise from 10,000/µL to 25,000/µL on a count drawn 30 minutes after a transfusion of 3.0 × 10¹¹ platelets. The patient's body surface area is 1.6 m². What is the corrected count increment (CCI)?

Incorrect. This enters the increment as 15, in thousands. The conventional formula uses counts per microliter: 15,000 × 1.6 ÷ 3.0 = 8,000.

Correct. The increment is 25,000 − 10,000 = 15,000/µL, and 15,000 × 1.6 ÷ 3.0 = 8,000, with the dose entered as the number of 10¹¹ platelets. A 10- to 60-minute CCI above 7,500 is the typical response in an afebrile, nonbleeding patient.

Incorrect. This uses the posttransfusion count of 25,000/µL. The CCI uses the increment, 25,000 − 10,000 = 15,000/µL.

Hint
  1. Start with the increment: the change in the count, in platelets/µL.
  2. The dose enters as the number of 10¹¹ platelets.

Review Platelet transfusion refractoriness

Problem 2 of 3 · Hints available

A neonate has severe thrombocytopenia, and fetal and neonatal alloimmune thrombocytopenia (FNAIT) is strongly suspected. The mother's routine platelet-antibody panel is negative. Which interpretation fits?

Correct. A routine panel detects only antibodies to its own antigens above its sensitivity, and an antibody can also be weak or develop late. A crossmatch of maternal serum with paternal platelets, family HPA genotyping, and reference-laboratory retesting 2 to 8 weeks after delivery can still show the incompatibility.

Incorrect. An antibody against a low-frequency or private paternal antigen, or a weak antibody, can be missed by a routine panel. The paternal platelet crossmatch can detect it.

Incorrect. The panel tests only for antibodies to its own antigens, so an alloimmune cause is not excluded. The history and counts are reviewed for other causes while the family investigation continues.

Hint
  1. Ask which antibodies a routine panel can detect.
  2. A father's platelets can carry an antigen that no panel cell carries.

Review Fetal and neonatal alloimmune thrombocytopenia

Problem 3 of 3 · On your own

A count drawn 15 minutes after a transfusion of 3.4 × 10¹¹ platelets is 25,000/µL. The count before the transfusion was 7,000/µL, and the body surface area is 1.7 m². What is the CCI?

Show the answer

9,000

The increment is 25,000 − 7,000 = 18,000/µL. CCI = 18,000 × 1.7 ÷ 3.4 = 9,000, a typical response for a count drawn 10 to 60 minutes after transfusion.

Review Platelet transfusion refractoriness

Use it

Read the case evidence, then make each decision. The step is complete without it.

  • A 66-year-old man receives one unit of plasma before a procedure.
  • Within 2 hours he has severe hypoxemia, new bilateral infiltrates and a blood pressure of 88/50 mm Hg.
  • His fluid balance is even, and his BNP is within the reference interval.
  • The clinical team and the transfusion service classify the reaction as TRALI and report it to the collecting facility.
  • The donor, a woman with four past pregnancies, is tested for granulocyte and HLA antibodies.
Decision 1 of 3

The first laboratory ran only a GIFT, and it was negative. What happens next?

GIFT alone can miss anti-HNA-3a, the antibody most linked to severe TRALI. A negative GIFT result is not enough to exclude a granulocyte antibody in the donor.

A second GIFT has the same limitation and can miss anti-HNA-3a again.

GIFT and GAT are used together. GAT improves detection of anti-HNA-3a.

Review HNA testing

Decision 2 of 3

The GAT finds anti-HNA-3a in the donor, and the recipient types HNA-3a positive. What does this pair show?

A donor antibody matching a recipient antigen supports an antibody-mediated mechanism for the lung injury. The collecting facility uses it in deciding about this donor's future plasma-rich donations.

The classification was already made from the clinical findings. The antibody result supports the mechanism.

Classified TRALI from a donor antibody result

TRALI is new acute lung injury with hypoxemia within 6 hours of transfusion. It is classified from those clinical findings and does not require an HLA or HNA antibody. A donor antibody matching a recipient antigen supports the immune mechanism and guides the donor evaluation.

An antibody result gives no information about volume status. His even fluid balance and a BNP within the reference interval argue against overload.

Review HNA testing

Decision 3 of 3

Had the donor shown no HLA or HNA antibody, how would the reaction be classified?

His fluid balance was even and his BNP was within the reference interval. A negative antibody result does not add signs of overload.

TRALI is new lung injury with low blood oxygen within 6 hours of transfusion. No antibody result is required to classify it.

The hypoxemia and infiltrates began within 2 hours of the plasma. A negative antibody result does not change that timing.

Review HNA testing

The donor's anti-HNA-3a matched the recipient's HNA-3a antigen, which supports an immune mechanism for the lung injury. GAT detected the antibody after the GIFT was negative. The TRALI classification is based on the clinical findings, with or without an antibody.

For reference

Sources checked