17.3 Platelet, Plasma, and Cryoprecipitate Therapy

17.3 Platelet, Plasma, and Cryoprecipitate Therapy

Quick Answer: One adult platelet dose (1 apheresis or a 4–6 unit whole-blood-derived pool) should raise a stable adult about 30–50 × 10^9/L. The corrected count increment (CCI) uses body-surface area and the platelet dose × 10^11; a 10–60 minute CCI < 5000–7500 on two occasions points to immune refractoriness. ABO-identical platelets are preferred; group O apheresis plasma into a non-O recipient can hemolyze. Give RhIG when D-positive platelets go to a D-negative woman of childbearing potential. TTP needs plasma exchange, not platelets. Vitamin K and 4-factor PCC are preferred for warfarin when available. Cryo dosing is a pool; the bleeding fibrinogen target is often 150–200 mg/dL.

This is June 9, 2026 outline V.B for platelets, plasma, and cryoprecipitate. Product identity and dating are Chapter 4.2. Triggers are 17.1. This section is increment, compatibility, and disease-specific use. If a stem asks CCI, refractoriness, out-of-group hemolysis, RhIG after platelets, TTP, PCC versus plasma, or cryo pools, answer it here.

Expected increment and CCI

A stable adult who is not bleeding, febrile, or splenomegalic should rise about 30–50 × 10^9/L one hour after an adult dose. Children are often dosed 5–10 mL/kg or about 10 mL/kg. Failure to increment is refractoriness, not a reason to keep issuing the same random product blindly.

Corrected count increment (CCI) normalizes the raw increment for body-surface area and dose:

CCI = (post − pre platelet count per µL × BSA in m²) / (platelets transfused × 10^11)

Count the increment in platelets/µL (which equals the increment in × 10^9/L × 1000), multiply by BSA, and divide by how many 10^11 platelets were in the bag. An apheresis unit is typically about 3–4 × 10^11. You need the pre-count, a 10–60 minute post-count, BSA, and the labeled yield. A 24-hour count is a survival check, not the immune-refractory screen.

A 1-hour CCI < 5000–7500 on two sequential, preferably ABO-compatible, transfusions is the usual definition of immune refractoriness. Those cutoffs are published formula conventions, not unpublished ASCP official numbers. Use them as the named method, not as Board-owned statutes.

Immune versus nonimmune refractoriness

Nonimmune consumption is more common: fever, sepsis, DIC, bleeding, splenomegaly, veno-occlusive disease, and some drugs (classically amphotericin). The 1-hour increment may be acceptable and the 24-hour count collapses, or both are poor without HLA antibodies. Treat the cause. HLA-matched platelets will not fix a spleen.

Immune refractoriness is usually HLA class I antibodies, less often HPA (platelet-specific) antibodies, and sometimes high-titer ABO isoagglutinins against A or B on the platelets. Work up with HLA antibody testing and, if needed, platelet crossmatch or an HPA workup. Therapy is HLA-matched or crossmatch-compatible platelets (17.4), ABO-identical units, and stopping random unmatched doses once the diagnosis is made.

Two failed 1-hour CCIs, not one noisy count drawn from the same arm as a running antibiotic, make the diagnosis. Draw the post-count from a different site than the infusion, and know the dose that was actually transfused.

ABO, plasma-incompatible platelets, and RhIG

ABO-identical platelets are preferred because the platelet increment is better (ABO antigens live on platelets) and because plasma isoagglutinins in the bag can hemolyze the recipient’s red cells. The dangerous mismatch is group O apheresis platelets — a large plasma volume with potentially high-titer anti-A or anti-B — given to a group A, B, or AB patient. Whole-blood-derived pools have less plasma per donor, but a pool can still hemolyze. Volume reduction or platelet additive solution reduces the plasma load when out-of-group is unavoidable.

D-positive platelets to a D-negative recipient can immunize because the product contains a small number of residual red cells. The patient who must not make anti-D is a woman of childbearing potential (and, in many services, girls). Give RhIG. A standard 300 µg vial covers far more than one platelet dose; some services use a microdose. D-negative men and women beyond childbearing often receive D-positive platelets without RhIG when D-negative inventory is tight. Do not give RhIG to a D-positive recipient.

Plasma therapy — TTP and warfarin are the exam pair

Plasma replaces soluble factors. Dose is 10–20 mL/kg when the goal is factor replacement. Indications were covered in 17.1; two disease rules dominate the exam.

TTP is a platelet-consumption and ADAMTS13 disease. First-line blood-bank therapy is therapeutic plasma exchange with plasma (FFP or a licensed plasma) to remove autoantibodies and replace ADAMTS13. Platelets are contraindicated except for life-threatening hemorrhage, because they can worsen microvascular thrombosis. Cryo is not an ADAMTS13 dose. Caplacizumab and immunosuppression are clinical adjuncts; the blood bank still has to issue plasma for exchange, not platelets to fix the count.

Warfarin lowers vitamin K–dependent factors (II, VII, IX, X, proteins C and S). If the patient is not bleeding and has time, give vitamin K. If the patient is bleeding or needs immediate reversal and a 4-factor prothrombin complex concentrate (PCC) is available, PCC plus vitamin K is preferred over plasma — less volume, faster INR correction, virally processed. Plasma remains acceptable when PCC is not available or when the patient also needs volume. Do not treat a nonbleeding INR of 2.0 with two FFP to be safe.

Cryoprecipitate dosing

An adult fibrinogen dose is a pool — commonly 5–10 single units (or a pre-pooled product), not one bag. A rough rule is 1 unit per 10 kg, which for a 70 kg adult is 7 units; many trauma packs issue a standard 5- or 10-unit pool and recheck fibrinogen. Each unit should contain ≥ 150 mg fibrinogen (Chapter 4.2), so a 5-unit pool is about 750 mg if every unit meets QC.

In bleeding, a commonly used fibrinogen target is 150–200 mg/dL. Obstetric hemorrhage protocols often aim ≥ 200 mg/dL. These are practice targets, not ASCP official unpublished cutoffs. Recheck the fibrinogen after the pool; one pool may not get a 40 kg blood-loss patient from 80 to 200 mg/dL.

Pathogen-reduced cryoprecipitated fibrinogen complex follows its own circular for thaw dating and dose. Do not overwrite it with the generic 6-hour / 4-hour clock if the stem names the licensed product.

Worked scenario. A 1.8 m² adult receives an apheresis unit labeled 3.6 × 10^11 platelets. Pre-count 6 × 10^9/L; 15-minute post-count 16 × 10^9/L. Increment = 10,000/µL. CCI = (10,000 × 1.8) / 3.6 = 5,000. That sits at the immune-refractory border. Repeat with an ABO-identical unit. If the second 1-hour CCI is again about 5,000, start HLA-matched or crossmatched platelets — do not keep issuing random group O apheresis units into this group A patient.

Exam traps. CCI uses BSA and dose, not a raw 5,000 platelet count. Immune versus nonimmune (sepsis, spleen, DIC). Group O apheresis can hemolyze. RhIG for D-positive platelets to D-negative women of childbearing potential. TTP = plasma exchange, not platelets. Warfarin: PCC + vitamin K when available. Cryo is a pool; target 150–200 mg/dL in bleeding.