Selected Topics in Pediatric Blood-Banking and Coagulation

Neonatal alloimmune thrombocytopenic purpura

(lack the offending antigen and antibody)

PLASMA COMPONENTS

Fresh frozen plasma (FFP)

factor activity, 200-250 mL volume ●● WBCs non-functional (no cryoprotectant) ●● Leukoreduction and irradiation are

unnecessary ●● It is frozen within 8 hours and preserves

labile factors V and VIII

Uses of FFP

●● Invasive procedure planned in a patient with documented coagulation factor deficiency

replacement fluid for TTP, HUS

Contraindications for FFP

●● Do not give for volume expansion/nutritional support

●● Colloids or protein containing solutions better for volume expansion/nutritional support, as no risk of viral transmission

Cryosupernatant

●● Cryo poor plasma used in patients who are refractory to initial treatment with FFP

●● Lacks large molecular weight Von Willebrand multimers

●● Prepared by removing cryoprecipitate from FFP

Cryoprecipitate

●● Prepared by thawing 1 unit of FFP at 1-6°C and removing the supernatant

●● Contains fibrinogen, factor VIII C, factor VIII VWF, factor XIII

●● Small volume (10-15 mL) allows more rapid replacement of coagulation factors than a single unit of FFP (200 mL)

hemophilia, despite high levels of factor VIII

●● Recombinant or virus-inactivated products remain the first-line therapy for hemophilia

●● Not the “product of choice” for treating Von Willebrand disease

●● Pharmacologic agents (DDAVP) or virusinactivated concentrates (Humate P) are primary therapies for VW disease

HEMOLYTIC DISEASE OF THE NEWBORN (HDN)

jaundice

●● Hydrops fetalis (most severe HDN, often fatal in utero, extra-medullary hematopoiesis in the liver)

Abo HDN

size, and thus cannot cross the placenta ●● Group O moms, Group A or B babies ●● No intervention necessary unless very

severe

Rh HDN

cross the placenta ●● Not manifested in first pregnancy (unless

mother has prior history of transfusion) ●● D-ve moms, D+ve babies ●● Prevention: RhIG-commercially prepared

anti-D (RhoGam)

Lab testing

elevated ●● Increased change in amniotic fluid optical

density at 450 nm (Liley graph)

RhoGam

●● Prevents D antigen recognition in vulnerable moms

●● Obstetric indications → D-ve female at 28 weeks’ gestation, D-ve female within 72 hours of D+ve infant’s birth, D-ve female with pregnancy complications or invasive procedures (e.g., amniocentesis)

●● Dosage: One full dose vial (30 µgm) per 30 mL of D+ve whole blood

●● Kleihauer-Betke test-quantitative test (acid-resistant HbF; fetal RBCs stain brightly)

●● KB% × 5/3 = number of vials required to be injected

EXCHANGE TRANSFUSION

●● Exchange transfusion indicated for HDN, hyperleukocytosis, or sickle cell anemia

●● Purpose of exchange transfusion will determine recommended hematocrit and amount of fresh frozen plasma to be used in reconstituted unit

●● Compatability testing: Mother’s serum may be used for crossmatch

CONGENITAL HEMOGLOBINOPATHIES

Thalassemia

●● Transfusion improves oxygen-carrying capacity of blood

●● To suppress endogenous erythropoiesis that causes bony abnormalities

●● Transfuse every 3-4 weeks at a dose to maintain pre-transfusion Hb of 9.5-10.5 g/ dL and posttransfusion Hb of 13-13.5 g/dL

ABO SELECTION OF BLOOD COMPONENTS

When transfusing whole blood/packed RBCs

When transfusing plasma

SELECTION OF RBCs (IMMUNOLOGICAL CONSIDERATIONS)

●● Everyone can receive “O” RBCs. Most receive group-specific RBCs

●● D-positive individuals can receive D-positive or D-negative RBCs

NEONATES

blood group and maternal blood group ●● For simplicity, many transfusion services

transfuse group O to all neonates ●● Antibody screen must be done prior to

neonatal transfusion either using neonate’s serum or mother’s serum

●● Coagulation system is divided into five components: Vascular endothelium, circulating platelets, coagulation factors, coagulation inhibitors, and fibrinolysis

Vascular endothelium

tion by secreting platelet inhibitors such as prostacyclin PGI2 and nitric oxide, thus preventing platelet adhesion

●❑ It also secretes fibrinolytic proteins such as tissue plasminogen activator tPA and plasminogen activator inhibitor PAI

bogenesis; platelet adhesion stimulated by subendothelial collagen and von Willebrand factor (vWF)

●❑ Tissue factor activates the extrinsic coagulation cascade

●❑ Factors V and VIII are released triggering thrombosis

Platelets

●● Help in thrombosis by platelet adhesion (GP Ib), activation, and aggregation (IIb/IIIa)

●● Platelets cross-link to each other thus stabilizing the fibrin clot

Coagulation proteins

●● Extrinsic (factor VII and tissue factor), intrinsic (contact activation, XII, XI, IX, and VIII),

and the common pathway (X, V, prothrombin, thrombin, fibrinogen, fibrin, stable clot)

●● End result is cleavage of fibrinogen and formation of fibrin clot

●● Thrombin is the gatekeeper of the entire clotting cascade

Coagulation inhibitors

●● Antithrombin III and heparin cofactor II (both members of SERPIN family) inhibit the fact or Xa/thrombin pathway

●● Activated protein C/S prevent thrombogenesis by blocking factor Va and factor VIIIa in the clotting cascade

●● Tissue factor pathway inhibition is done by two serine protease inhibitors TFPI-1 and TFPI-2

Fibrinolysis

●● Process by which a thrombus/clot is removed from intravascular/extravascular site

●● The proteolytic enzyme that aides in this process is plasmin (produced from plasminogen)

HEMORRHAGIC DISEASE OF THE NEWBORN

●● Coagulation factors II, VII, IX, and X are produced in the liver and are dependent on vitamin K

●● After birth, the levels of these factors normally fall very rapidly

●● Unless vitamin K (1 mg intramuscularly) is administered prophylactically to all newborns, there may be risk of hemorrhage

●● Risk factors for vitamin K deficiency are antibiotic treatment, exclusive breastfeeding, conjugated hyperbilirubinemia

THROMBOPHILIA IN NEONATES AND CHILDREN

●● Genetic factors: Factor V Leiden, prothrombin mutation, protein S and C deficiency, antithrombin deficiency

●● Common sites of thrombosis in neonates: Renal veins, vena cava, central lines, catheter sites

should include AT III levels, protein C activity, free and total protein S antigen/activity, factor V Leiden, prothrombin G20210A, MTHFR T677T, fasting homocysteine level

●● If the mother has a history of lupus; perform circulating lupus anticoagulant and anticardiolipin antibodies

MATERNAL THROMBOPHILIA AND EFFECTS ON PREGNANT MOTHER/FETUS

●● Pregnancy is normally a thrombophilic state due to various factors (overall risk of venous thromboembolism in pregnancy is 1:1000)

●● An underlying genetic thrombophilia further enhances the prothrombotic features of pregnancy

●● The high thrombotic risk is caused by antithrombin III (AT III) deficiency, homozygous factor V Leiden, and the combined defect (factor V Leiden + prothrombin G20210A)

●● Uteroplacental circulation is compromised causing fetal growth retardation, fetal death, placental abruption, pre-eclampsia

●● Placenta shows multiple infarcts and fibrinoid necrosis of fetal vessels

INHERITED FACTOR DEFICIENCIES

recessive trait, disease manifested if factor VIII levels between 5% and 50%

●❑ Markedly prolonged aPTT, normal PT, and normal BT

●❑ Reduced factor VIII:C and normal vWF:Ag and ristocetin cofactor

●● Factor IX deficiency (hemophilia B, Christmas disease) ●❑ Clinically indistinguishable from hemo-

philia A ●● Von Willebrand disease

●❑ vWF is a large multimeric glycoprotein synthesized in megakaryocytes and vascular endothelial cells, stored in

Weibel-Palade bodies in endothelial cells and alpha granules of platelets

reduced vWF Ag, decreased ristocetin cofactor, decreased vWF multimers

cord separation, bleeding from umbilical stump, and hemorrhage at circumcision site

●❑ Screening test: Abnormal clot solubility in 5M urea

●● Antithrombin, protein C, and protein S deficiencies

replaced by glutamine ●❑ Bimodal peaks: Neonates and children

11-18 years old ●● Prothrombin gene 20210A mutation

●❑ Glutamine to arginine mutation at prothrombin gene at position 20210A

DISSEMINATED INTRAVASCULAR COAGULOPATHY (DIC)

●● Life-threatening microvascular thrombotic condition caused by a variety of insults

●● Laboratory screening: Prolonged aPTT, PT, elevated D-dimer and decreased fibrinogen, plasma factors, and platelets

THROMBOTIC MICROANGIOPATHIES

Thrombotic thrombocytopenic purpura (TTP)

●● Combination of profound thrombocytopenia, hemolytic anemia, and schistocytosis

●● Presence or absence of fever, neurologic symptoms, and renal failure

●● Primary and acquired TTP is caused by deficiency of ADAMTS13, a plasma metalloprotease that cleaves von Willebrand factor. May also be secondarily caused by drugs, infectious colitis

●● Platelet-rich thrombi noted in heart, pancreas, kidney, adrenal gland, brain, and other organs

●● Fibrin/red cell rich thrombi seen mostly confined to kidney

Stec-HUS

ing Escherichia coli (STEC-HUS) ●● E. coli O157:H7 accounts for 60% of cases

Atypical HUS

alternative complement pathway

Note

●● TTP and HUS are pathologically distinct entities, although they are clinically indistinguishable sometimes

●● Differentiation of TTP from HUS in pediatrics is critical

●● A life-saving treatment (plasma exchange therapy) is available for TTP, but only supportive therapy/renal dialysis for HUS