14.2 Component Therapy
Key Takeaways
- One apheresis platelet unit (or an equivalent pool of 4-6 whole-blood-derived units) is expected to raise an average adult's platelet count by roughly 30-60 x10^9/L absent ongoing consumption.
- A corrected count increment (CCI) persistently below about 5,000-7,500 at 1 hour post-transfusion signals platelet refractoriness and should trigger investigation for immune (HLA/HPA antibody) versus nonimmune (fever, DIC, splenomegaly, sepsis) causes.
- Irradiation prevents transfusion-associated graft-versus-host disease and is required for HSCT recipients, purine-analog chemotherapy recipients, intrauterine transfusion, and directed donations from blood relatives, among other high-risk groups.
- Washing removes residual donor plasma proteins for patients with recurrent severe allergic reactions or IgA deficiency with anti-IgA; it is a different fix from leukoreduction, which targets febrile reactions, HLA alloimmunization, and CMV transmission risk.
- Plasma is dosed at roughly 10-15 mL/kg to raise factor levels about 20-30%, and cryoprecipitate is dosed to target a fibrinogen rise, commonly using a pool of 4-6 units in a bleeding patient with hypofibrinogenemia.
Matching the component to the defect
Component therapy questions on the SBB exam usually present a clinical deficit and ask which product, and which modification of that product, fixes it. The starting logic never changes: red cells restore oxygen-carrying capacity, platelets restore platelet number or function, plasma restores multiple coagulation factors, and cryoprecipitate restores fibrinogen and a narrow set of other factors.
| Clinical deficit | Best product | Common trap |
|---|---|---|
| Symptomatic anemia or acute blood loss | Red blood cells | Plasma does not correct anemia |
| Thrombocytopenia or platelet dysfunction with bleeding/procedure need | Platelets | Red cells do not correct platelet count |
| Multiple coagulation factor deficiency with bleeding or urgent reversal | Plasma (or factor concentrate/PCC per policy) | Plasma is not a volume expander |
| Hypofibrinogenemia with bleeding (obstetric hemorrhage, DIC, trauma) | Cryoprecipitate (or fibrinogen concentrate) | Platelets do not replace fibrinogen |
| Severe neutropenia with refractory bacterial/fungal sepsis unresponsive to antibiotics | Granulocytes (rare, time-sensitive) | Granulocytes are not a substitute for antimicrobial therapy |
Dosing and expected response
Quantifying the expected response is what separates specialist-level questions from generalist ones.
Red blood cells. One adult RBC unit (roughly 250-300 mL) is expected to raise hemoglobin approximately 1 g/dL (hematocrit approximately 3%) in an average-sized adult without ongoing loss. A rise smaller than expected after appropriate dosing should prompt investigation for occult bleeding, hemolysis, or a dilutional/consumptive process, not simply another unit ordered reflexively.
Platelets. A single apheresis platelet unit contains roughly 3 x10^11 platelets and is the dose-equivalent of pooling 4-6 whole-blood-derived (random-donor) platelet units. In an average adult without ongoing consumption, this dose raises the platelet count by roughly 30-60 x10^9/L. When the response is inadequate, calculate the corrected count increment (CCI):
A CCI below roughly 5,000-7,500 at 1 hour, or below roughly 4,500 at 18-24 hours, on repeated ABO-compatible transfusions defines platelet refractoriness. The exam expects you to split the differential: immune causes (HLA Class I alloantibodies, less commonly HPA alloantibodies) versus nonimmune causes (fever, sepsis, DIC, splenomegaly, amphotericin B, some antibiotics). Immune refractoriness is managed with HLA-matched or crossmatch-compatible platelets; nonimmune causes are managed by treating the underlying consumptive process.
Plasma. Typical dosing is 10-15 mL/kg, which raises most coagulation factor levels by roughly 20-30% — generally enough to support hemostasis for factors with a hemostatic threshold in that range.
Cryoprecipitate. Dosing targets a fibrinogen increase; a standard pool (commonly 4-6 units, or an equivalent pathogen-reduced pooled product) is a typical adult dose for hypofibrinogenemic bleeding, with the exact rise dependent on baseline fibrinogen, plasma volume, and consumption.
Special processing and modifications
Modifications solve specific problems — they are not interchangeable, and the exam tests that distinction directly.
| Modification | Purpose | Key indications |
|---|---|---|
| Irradiation | Prevents transfusion-associated graft-versus-host disease by inactivating donor lymphocytes | HSCT recipients, intrauterine transfusion, congenital cellular immunodeficiency, purine-analog chemotherapy (e.g., fludarabine), directed donations from blood relatives, HLA-matched/crossmatched platelets |
| Leukoreduction | Removes most donor white cells | Reduces febrile nonhemolytic reactions, HLA alloimmunization, and CMV transmission risk; increasingly performed pre-storage as a universal practice |
| Washing | Removes residual donor plasma proteins | Recurrent severe/anaphylactic allergic reactions, IgA deficiency with anti-IgA, neonatal exchange transfusion |
| CMV-seronegative selection | Provides serologically CMV-negative product | Alternative or adjunct to leukoreduction for intrauterine transfusion, low-birth-weight neonates, CMV-negative pregnant patients, and CMV-negative transplant candidates |
| Volume reduction | Concentrates the product into a smaller volume | Neonates and patients with cardiac or renal compromise who cannot tolerate standard volumes |
| Frozen deglycerolized RBCs | Extends storage of rare phenotypes | Preserves rare units for years frozen; requires deglycerolization and has a short post-processing outdate (commonly 24 hours in an open system) |
A frequent exam trap: leukoreduction and washing are not interchangeable. Leukoreduction removes white cells and lowers febrile/HLA/CMV risk; it does not meaningfully remove plasma proteins, so it will not fix a severe allergic reaction. Washing removes plasma proteins but is not a validated substitute for irradiation against graft-versus-host disease.
Massive transfusion component strategy
Beyond individual dosing, mass-casualty and major hemorrhage settings increasingly use ratio-based component therapy (near 1:1:1 RBC:plasma:platelet) or low-titer group O whole blood (LTOWB) where available, both intended to approximate the composition of whole blood and limit dilutional coagulopathy, before transitioning to viscoelastic-guided (TEG/ROTEM) targeted component replacement once results are available.
Newer platelet processing: additive solution and pathogen reduction
Two processing trends show up increasingly on specialist-level exams. Platelet additive solution (PAS) replaces most of the donor plasma surrounding apheresis platelets with a nutrient/buffer solution, which reduces plasma-protein exposure (lowering allergic and febrile reaction rates) while preserving platelet count and function — a distinct mechanism from washing, which is performed on demand rather than at collection. Pathogen-reduction technology (for example, amotosalen/UV or riboflavin/UV treatment) inactivates residual white cells, bacteria, and many viruses in platelets and plasma; in some jurisdictions a validated pathogen-reduction step is accepted in place of routine bacterial culture and, in certain systems, in place of gamma irradiation for GVHD prevention specifically in that treated component. The exam expects you to recognize pathogen reduction as a distinct safety strategy from irradiation and leukoreduction, not a universal replacement for every modification.
Granulocyte concentrates
Granulocyte transfusion is a narrow, time-critical therapy reserved for severely neutropenic patients with bacterial or fungal infection that is progressing despite appropriate antimicrobial therapy, most often in the setting of anticipated marrow recovery (post-chemotherapy or post-transplant). Donors are typically mobilized with corticosteroids or growth factor (G-CSF) to increase collection yield. Because the product's entire value is its white cell content, granulocytes are never leukoreduced, are always irradiated to prevent GVHD from the very high lymphocyte content, and must be transfused as soon as possible after collection since granulocyte function declines rapidly during storage.
A patient's platelet count fails to rise appropriately after two ABO-compatible apheresis platelet transfusions, with a corrected count increment (CCI) consistently below 5,000 at 1 hour post-transfusion. What should be investigated first?
Which patient most clearly requires irradiated cellular blood components to prevent transfusion-associated graft-versus-host disease?
A patient has a documented severe recurrent allergic reaction to plasma proteins despite antihistamine premedication. Which modification is most appropriate for future RBC transfusions?
Match each component modification with its primary purpose.
Match each item on the left with the correct item on the right