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Hematology Pathophysiology: Transfusion Medicine (O’Malley)
RED CELL ANTIGENS AND BLOOD GROUP ANTIBODIES:

Basics:
Over 400 RBC antigens described on surface of RBC
o Abs may form against any of these Ags
o Formation of Abs may occur naturally (people lacking the Ag) or following exposure to blood (ie.
pregnancy, transfusion)
Clinical importance of Abs is determined by temperature of Ag-Ab reaction
o Naturally Occurring Abs (IgM):

Clinically significant if they react in vivo at body temperature (ie. anti-A and anti-B)

Not clinically significant if they only react at cold temperature
o Immune Induced Abs (IgG):

Warm reacting Abs that are always clinically significant

May not fix complement (but can)

Cross the placenta

ABO Blood Group:
Most Important Blood Group for Transfusion: one in which the absence of an Ag is ALWAYS followed by natural
occurrence of corresponding IgM Ab
o Fix complement  intravascular hemolysis
o Abs to A and B blood groups are involved in FATAL transfusion reactions
Genetics of ABO Blood Groups:
o Individual inherits one ABO gene from each parent (2 genes together determine ABO Ags on RBCs)

ABO loci is at cs 9
o Three different genes:

O gene: amorphous allele that adds NO sugar

A and B genes: co-dominant; code for specific transferases that attach the immunodominant
sugar to a precursor substance (H chains)
 A gene: encodes for N acetylgalactosaminyl transferase
 B gene: encodes for galactosyltransferase
Formation of A, B and H Antigens:
o H Chains: required for the placement of A and B antigens onto the RBC

H gene codes for L-fucosyltransferase (adds L-fucose to paragloboside  H chain)

A gene places A antigen on H chain

B gene places B antigen on H chain

O gene is amorphous, and H chains remain unmodified
o A Antigen: N acetyl galactosamine
o B Antigen: galactose
Distribution of ABO Ags:
o A,B an O antigens are expressed on all epithelial cells in the body

Critical in solid organ transplantation (ABO incompatability  hyperacute rejection)
o 80% of the population have the SECRETOR GENE, that also causes the presence of ABO substances in
secretions (ie. saliva, tears, GI secretions)
Naturally Occurring Abs Based on Genotype:
o OO: anti-A and anti-B
o AA or AO: anti-B
o BB or BO: anti-A
o AB: none

Rh Blood Group:
RhD: most important of the Rh Ags (very immunogenic)
o 80% of Whites and 90% of Blacks have D antigen
o 70% of people exposed to the Ag only ONCE will form Abs to it (IgG- do not occur naturally)
o Red cell transfusions are matched for D antigen (IgG Abs implicated in transfusion reactions)
o IgG Abs may cross placenta and cause HDFN
RhCE: less common Rh Ag that occurs through alternate splicing of two proteins encoding for Cc and Ee
o Anti-E/e/C/c are much less common

Other Blood Groups:
Clinical Significance: to be clinically significant, Abs must bind to Ag at 37C
o Many of these Ags are weakly immunogenic and/or have low frequency
-
o Matching ABO and D blood types results in a safe transfusion 98% of the time
Chronically Transfused Patients: may develop multiple clinically significant Abs (may delay availability of blood
for transfusion)
Some Other Clinically Important Blood Groups:
o Kell: occasional frequency (may cause HTR and HDFN)
o Duffy: occasional frequency (may cause HTR and HDFN)
o Kidd: occasional frequency (may cause HTR and HDFN)
o Lutheran: rare frequency (may cause HTR, but NOT HDFN- usually not IgG)
o Lewis: occasional frequency (may cause HTR, nut NOT HDFN- usually not IgG)
BLOOD BANK TECHNIQUES:

Direct and Indirect Coombs Test (Direct and Indirect Antiglobuin Test):
Hemagglutination: ability of RBC Abs to agglutinate cells expressing Ag in question
o IgM Abs: cause hemagglutination directly at room temperature (anti-A and anti-B)
o IgG Abs: require incubation at 37C to bind Ag + addition of antihuman globulin (anti-IgG) to cause
agglutination (IAT)
Indirect Antiglobulin Test (IAT/Indirect Coombs Test):
o Basics: tests for presence of Abs present in patient SERUM to test RBCs
o Process:

Incubate cells with serum for in vitro binding

Wash excess Abs

Add anti-human globulin serum (anti-IgG)  if agglutination occurs, test is (+)
o Use:

Crossmatching the donor’s RBCs with patient’s serum

Detection of Abs to RBCs in the patient’s serum
Direct Antiglobulin Test (DAT/Direct Coombs Test):
o Basics: tests for Abs already bound to patient’s RBCs
o Process:

Wash red cells with saline to remove excess serum

Add anti-human globulin  if agglutination occurs, test is (+)
o Use: for the diagnosis of various hemolytic reactions:

HDFN

AIHA

Drug-induced hemolytic anemia

Hemolytic transfusion reactions

Pretransfusion Testing:
Determination of ABO and Rh Groups:
o ABO Grouping: interpretation of forward and reverse grouping much match

Forward Grouping: patient’s RBCs tested against anti-A and anti-B

Reverse Grouping: patient’s plasma tested against A1 cells and B cells
o Rh Type: determined by testing patient RBC’s with anti-D

Recall that if you are Rh negative, you do NOT have anti-D Abs (unless you have been
exposed to D antigen (+) blood)

Therefore, doing a reverse grouping (ie. testing patient’s plasma against RhD(+) cells) is not
useful
Antibody Screen:
o Basics: patient’s SERUM is incubated with cells expressing all Ags that cause significant Abs

Screening cells (I and II) are ALWAYS O type and have good expression of clinically significant
antigens (ie. Duffy, Kell, Kidd, RhCcEe)
o Results:

Antibody Screen Negative: transfusion of ABO Rh compatible blood to a patient with a
NEGATIVE Ab screen is considered safe (we would expect the crossmatch to be compatible)

Antibody Screen Positive: must do an antibody identification panel with ~14 known cells to
determine the Ab
 Once Ab determined, blood bank units are phenotyped to be negative for
corresponding Ags
Crossmatch:
o Basics: patient’s serum is added to ABO, Rh matched donor RBC
o


Process:

Immediate Spin: ABO compatibility confirmed after centrifugation

Indirect Coombs Test: continuation of crossmatch required if patient determined to have
clinically significant Abs on Ab screen
 Required to determine if unit selected is compatible
Type and Screen:
Should be ordered if transfusion may be needed, but is not very likely
o Examples: C-section, cholecystectomy
Type and Crossmatch:
Should be ordered if transfusion is very likely
COMPLICATIONS OF TRANSFUSION:

Typical Causes of Transfusion Associated Deaths:
Acute hemolysis (ABO-incompatbile blood components; WBIT- wrong blood in tube)
Acute pulmonary edema (TACO, TRALI)
Bacterial contamination of product
o Compromised blood sterilization
o Donor with asymptomatic bacteremia (sometimes seen with Crohn’s disease)
Delayed hemolytic reactions (DHTR)
Anaphylaxis
External hemolysis of RBCs (temperature exceeded 40C)
Damaged blood component (ie. nondeglycerolized, improper solution)
GVHD

Early Complications of Transfusions:
Hemolytic Reactions: ~1/60,000 transfusions
o Classification:

By Mechanism:
 Immune hemolysis (due to Abs)
 Non-immune hemolysis

By Site of Hemolysis:
 Intravascular
 Extravascular

By Onset in Relation to Transfusion:
 Immediate
 Delayed
o Mechanism: occurs when the patient receives RBCs with antigens to which the patient has Abs

Abs bind to Ags on the surface of donor cells, leading to hemolysis of RBCs
 Abs coating RBCs  positive Direct Coombs test
 May be negative if ALL cells coated with Ab have been destroyed

Site of destruction is a function of ability of Ab to activate complement
o Site of Destruction: both types may be LIFE-THREATENING

Intravascular Hemolysis: IgM or IgG Ab that can FULLY activated complement
 Results in destruction of RBC intravascularly
 Formation of intravascular immune complexes and RBC intracellular components
results in:
o Hemoglobinemia and hemoglobinuria
o DIC
o Acute tubular necrosis

Extravascular Hemolysis: Ab does NOT FULLY activate complement (activated up to C3)
 Ig covered RBCs removed from circulation by the RES
 Usually results in MILDER hemolysis, but can also be life-threatening*
o Delayed HTR:

Basics: Abs present at levels below detection by pretransfusion testing

Process: re-exposure to antigen causes an anamnestic response in 3-7 days
 Abs cause accelerated RBC destruction (usually EXTRAVASCULAR)
 Patients present with mild symptoms (usually anemia and jaundice)
o Clinical Features of Severe HTR:

Lumbar (back) and precordial (chest) pain
-
-
-

Fever and chills

SOB

Anxiety

Hypotension (may be masked by anesthesia if it occurs during surgery)

Hemoglobinemia and hemoglobinuria

DIC

Acute tubular necrosis (renal failure)
o Investigation of HTR:

STOP TRANSFUSION IMMEDIATELY*
 Need to push fluids to protect kidneys

Check for clerical errors (ie. WBIT- most common cause of severe HTR)

Send donor unit and post-transfusion blood sample to the blood bank
 Repeat ABO, Rh typing on pre- and post-transfusion samples
 Repeat crossmatch to Coombs
 Perform direct Coombs on post-transfusion sample
 Check for free Hb in plasma and urine
 Check donor unit for bacterial contamination
 Baseline testing for DIC (D-dimers, decreased platelets and fibrinogen)

Send urine to the lab (hemoglobinuria)

Start treatment
o Management of HTR:

Most Severe Consequences of HTR:
 Renal failure
 DIC

Important Management Principles:
 Maintain hydration and diuresis:
o Diuresis at 100/mL per hour (with saline and furosemide)
o Monitor urinary output
 Treat DIC if present:
o Transfuse platelets and FFP
o Treat shock with antihistaminics and steroids (may require vasoporessors
like DA as well)

Management of Delayed HTR:
 Similar to acute HTR, but renal failure occurs less often
o Prevention of HTR:

PREVENTION IS THE KEY:
 Ensure correct sample and patient identification
 Monitor transfusion and stop at the first sign of reaction (ie. fever, pain at
transfusion site)
o No fatal reaction has occurred in patients who received less than 200 mL
of incompatible blood
 AVOID UNNECESSARY TRANSFUSIONS*
Sepsis (Bacterial Contamination):
o Basics: 2nd most common cause of fatal post-transfusion reactions*

More common with platelet transfusions (platelets are stored at room temperature)

Usually due to Gram(+) cocci (ie. Staphylococci)
o Presentation: very high fever OR circulatory collapse w/o fever
o Treatment: immediate broad spectrum antibiotics (may prevent death)
Allergic Reactions:
o Cause: IgE antibodies to donor plasma proteins (most commonly IgA)
o Presentation: can vary in severity from urticaria (hives) to anaphylactic shock (rare)
o Mechanism: transfused allergen reacts with preformed IgE on the surface of mast cells, activating
them (release of histamine  pruritus, bronchospasm, cramping and hypotension)
o Treatment: antihistaminics (ie. Benadryl) or epinephrine to treat anaphylactic shock
o Prevention: washed RBCs prevent repeat reactions
Non-Hemolytic Febrile Reactions:
o Definition: increase in temperature of more than 1C over baseline that occurs during or within 24
hours of transfusion (minimum temperature of 38C)
o

Cause:


Abs to WBCs in the donor unit, OR
Presence of cytokines released by WBC (cause hypothalamus to produce PGE-2 change in
the rate of thermoregulation and fever)
 May be due to release of cytokines during storage or in vivo
o Presentation:

Increase in temperature to at least 38C

Some symptoms in common with HTR and bacterial contamination (need to rule out first)
 Diagnosis of EXCLUSION*
o Prevention: partly prevented by LEUKODEPLETION (removal of WBCs)
Fluid Overload (Transfusion-Associated Circulatory Overload or TACO):
o Signs:

Dyspnea

Headache

Heart failure

JVD
o At Risk Patients:

Patients with low cardiac reserve (elderly, severely anemia, CHF)

Patients with low blood volume (ie. children and infants)
o Prevention: prevented by slow administration of blood

All patients should always be infused a rate that is well tolerated
 Usual rate for NON-BLEEDING patient is 2ml/kg/hour

Patients at risk should be transfused at a lower rate 1ml/kg/hour
 Diuretics may also be useful for these patients to prevent volume overload
 Blood banks may aliquot units upon request
Citrate Toxicity:
o Basics: citrate is used as an anticoagulant in stored blood (binds up Ca++)
o Presentation:

Perioral tingling (give tums to replenish some Ca++)

Severe cases may result in tetany (give Ca++ supplements to prevent)
Hyperkalemia:
o Basics: K+ release from RBCs occurs in storage (ie. issue seen with older blood
o Prevention: patients with low blood volume (ie. children) get the freshest blood
Clotting Abnormalities (Massive Transfusion)
Transfusion Related Acute Lung Injury (TRALI):
o Signs:

Acute respiratory distress (reaction resembles ARDS)

Pulmonary edema (non-cardiogenic)

Hypoxemia

NO changes in cardiac status
o Cause: presence of donor Abs to HLA antigens of the recipient

PE occurs because of microvascular occlusion and capillary leakage

HLA specific Abs are often seen in multiparous females (ie. many pregnancies)
o Diagnosis: TRALI is also a diagnosis of EXLCUSION

BNP Level: may help distinguish between TRALI and TACO
 BNP elevated in TACO, normal in TRALI
Late Complications of Transfusions:
Infections:
o Viral: HIV, CMV (important in immunocompromised patients- prevented by leukodepletion), WNV,
Hepatitis C, Hepatitis B (highest risk- 1/300,000)
o Bacterial: treponema, brucella, salmonella, yersinia enterocolitica (loves both cold temperature of RBC
storage and high iron content)
o Parasites: malaria, toxoplasma
Iron Overload:
o Amount of Iron in One Unit RBC: 250mg
o Mechanism: seen in patients who are CHRONICALLY transfused

Iron accumulates in RES first, and then parenchymal cells of vital organs
o
-
Prevention: administration of iron chelators and methods to decrease the number of transfusions
needed (ie. exchange transfusion for sickle cell disease)
Immune Sensitization: Ab production for future transfusions
o Results in greater difficulty finding matched blood
Transfusion Associated Graft vs. Host Disease (TA-GVHD):
o Mechanism: T lymphocytes of DONOR origin recognize antigenic disparity with the recipient if they are
not destroyed by the recipient (ie. if recipient is immunocompromised)
o Fatality Rate: over 90%
o At Risk Patients: patients with T cell immunity failure (ie. HIV, treatment with chemotherapy)
o Prevention: 100% prevented by irradiation of cellular blood components

Blood bank needs to be informed patients are at risk in order to irradiate
BLOOD PRODUCTS:

General Process of Collection:
One Unit of Blood: 500ml (collected aseptically)
Anticogulation: citrate added to chelate Ca++ and prevent coagulation
Unit Testing:
o ABO and Rh typing
o Ab screen
o Serologic test for syphilis
o Hepatitis B surface antigen
o Hepatitis C antibody
o HIV-I and HIV-II screening and confirmatory test
o HTLV-I and HTLV-II antibodies
o Nucleic acid testing for HIV, HCV and HBV
Preparation of Components: see below
Storage of RBCs: stored at 4C with expiration date of 35-42 days
o Storage Changes to RBCs:

Increased plasma K+ (fresh blood should be used for exchange transfusions of newborns)

Loss of 2,3-DPG (increased affinity of Hb for O2- reversible 24 hours after transfusion)
o Maintenance of ATP Levels: addition of dextrose, adenine and mannitol (critical for cell’s survival)

Component Preparation:
Centrifugation of Whole Blood: 500mL (one unit) centrifuged
o Cellular Components: RBCs, platelets, WBCs

Hard Spin: separation of platelets (top) from RBCs and WBCs (bottom)
o Fresh Plasma: supernatant

Fresh Frozen Plasma: frozen within 8 hours of collection (-18C)
 Cryoprecipitate: thaw FFP at 6C and cold centrifuge
o Factor VIII Concentrate
o Fibrinogen
 Cryosupernatant: supernatant from cold centrifuge
o Albumin
o Immunoglobulins
o Other concentrates

Leukocyte Depletion:
Basics: removal of WBC from blood by filtration before storage
o Defined as less than 5x106 WBC/unit
Function:
o Decreases incidence of febrile reactions
o Prevents CMV transmission
o May prevent alloimmunization to HLA antigens
TYPES OF TRANSFUSIONS:

Autologous Transfusions:
Predeposit: may be used for ELECTIVE surgery
o Basics: patient’s own blood is pre-deposited before patient goes into surgery
o Contraindications: anemia, acute infections
o Limitations: high cost, wasteful (unused blood is discarded), only for elective surgery
-


Hemodilution:
o Basics: blood removed early in the surgical procedure and volume restored with fluids

Only 2 units of blood may be collected at the time of surgery and replaced with saline

If blood is needed, reinfuse the last unit first
Salvage:
o Basics: blood is recovered and reinfused during surgery from a surgical wound
o Limitations: can only be collected during clean surgery (ie. not during abdominal surgery or surgery for
malignancy)
Red Blood Cell Transfusion:
Components: RBC concentrate (300mL) with very little plasma
o Red cells may be washed to remove plasma (increases O2 carrying capacity)
o Most components are leukocyte depleted (100% at DMC)
Indications for Use:
o Key Point: Hb level SHOULD NOT be the trigger for transfusion; the patients SYMPTOMS are the best
indicators for the need to transfuse

Patients with Hb less than 6g/dL would probably benefit from transfusion

Patients with Hb greater than 10 g/dL probably would not benefit
o Unnecessary Transfusions=BAD

Transfusions for anemias that can be corrected by other methods (ie. iron, EPO, B12, folate)
SHOULD BE AVOIDED

All hospitals monitor transfusions

Chart documentation of rationale for transfusion is VERY important
Effects: expected increment of 1g Hb/dL for increase for unit transfused
Platelet Transfusion:
Components Available:
o Random Donor Platelet Unit: from one unit of whole blood

Increases the platelet count by 5000/uL

Given in pools of 5-6 units
o Single Donor Platelet Unit: apheresis platelets (obtained by apheresis)

Increases the platelet count by 30,000-40,000/uL (in a HEALTHY patient; often don’t attain
this goal in patients requiring transfusions)

Given as a single unit
Indications for Use: used to correct thrombocytopenias or functional defects in platelets
o Patient needing major invasive procedure with platelet count <50,000/uL

Want count >100,000/uL if intracranial or intraocular surgery
o Patient bleeding with platelet count <50,000/uL
o Prophylaxis against bleeding for thrombocytopeinia of <5000-10,000/uL
o Patient with qualitative platelet disorder who is bleeding or needs surgery, irrespective of platelet
count
o Patients on platelet inhibitor drugs who are bleeding or have an upcoming emergent surgery
Contraindications:
o TTP/HUS
o HIT
Not Helpful in ITP: have Abs to platelets (would just destroy infused platelets)
Refractoriness to Platelet Transfusions:
o Result: poor platelet count increment post-transfusion
o Causes:

Non-Immune: most common*
 Sepsis
 Hypersplenism
 Some antibiotics and antifungals
 DIC
 Patient’s disease

Immune:
 Anti-HLA antibodies formed by exposure to WBC (ie. transfusion, pregnancy)
 Anti-PMN antibodies
o Prevention of Immune Causes: transfuse HLA compatible platelets or crossmatch

Transfusion of leukodepleted blood prevents the occurrence in the first place





Fresh Frozen Plasma:
Description and Contents: plasma from one unit of blood frozen within 8 hours and stored at -18C
o Contains all coagulation factors
Indications: most OVER-UTILIZED of the blood components* (at least 30% of transfusions are not indicated)
o Correction of coagulation disorders due to:

Multiple factor deficiencies (DIC, massive transfusion, liver failure), OR

Specific factor deficiencies when purified product is not available
o Rapid reversal of Coumadin anticoagulation
o TTP and HUS (plasma exchanges)
Cryoprecipitate:
Description and Contents: thaw FFP at 6C, centrifuge, and store precipitate frozen
o Contains factor VIII and vWF
o Source of fibrinogen (usually 250mg fibrinogen/bag; standards require at least 150mg)
Indications:
o Hypofibrinogenemia (<100mg/dL)
o No longer used for hemophilia A and vWF (recombinant factor VIII and desmopressin are safer)
Albumin:
Use: good volume expander due to its sustained osmotic effect
o Best initial replacement for blood loss
o Replacement of choice for most plasma exchange procedures
Pros: free of infectious agents (pasteurized)
Cons: expensive
Immunoglobulins:
Indications:
o Hypogammaglobulinemias
o Acquired immune disorders (ITP, NAIT)
Specific Immunoglobulins: contain high titers of specific Abs to
o D antigen (Rh immunoglobulin)

Rhogam used in pregnancy for Rh(-) mothers
o Hepatitis B

Given to patients with exposure to Hep B (prevent them from getting it)
o Rubella
Use of Blood Components in Specific Clinical Situations:
Acute Blood Loss: blood volume decreases WITHOUT initial changes in Hb levels
o When blood volume is corrected, Hb drops
o Increased production of new red cells  increased reticulocyte count

Occurs 2 days after blood loss (maximum retic count at 8 days)

Hb will increase by day 7 with iron treatment
o Transfusion should be based on estimated blood loss and symptoms (NOT Hb)
Massive Transfusion: transfusion of one blood volume (10 units of RBCs) in 24 hours
o Accompanied by several features:

Thrombocytopenia (dilutional and predictable)
 75% of platelets with transfusion of one blood volume
 Corrected by platelet transfusion

Coagulopathy (dilutional but less predictable)
 Factors worsening coagulopathy with massive transfusion:
o Hypovolemia
o DIC
o Acidosis
 Corrected by transfusion of FFP based on PT and PTT values

Decreased fibrinogen may require cryoprecipitate (if <100 mg/dl)
HEMOLYTIC DISEASE OF THE FETUS AND NEWBORN (HDFN):

Definition: anemia of the fetus and newborn due to red cell destruction by maternal Abs crossing the placenta

Pathophysiology:
Maternal IgG antibodies to paternal RBC antigen cross the placenta and bind to fetal RBCs
Result is removal of RBCs by the RES system in the fetus and rapid red cell destruction
o Anemia, compensatory increased erythropoiesis, and organ damage (esp. heart failure)

Types:
ABO HDFN: most common type*
o Pathogenesis: due to ABO compatability between mother and fetus (occurs in ~20% of pregnancies)

Only O type mothers produce IgG anti-A an anti-B that can cross the placenta (mothers with
other ABO types onyl produce IgM)

Because the Abs are pre-existing, this form may affect the first pregnancy
o Presentation: usually mild (slight anemia and jaundice)
o Treatment: phototherapy
-




Rh HDFN: less common but more severe*
o Pathogenesis:

RhD negative mother sensitized to D Ag by a first pregnancy with a D positive fetus
 May also be sensitized by abortion, amniocentesis or placental trauma

IgG Ab can cross the placenta in subsequent pregnancies and cause HDFN in RhD + fetus
Other Blood Group HDFN:
o IgG antibodies may form to other blood groups, but it is very rare (anti-K, anti-Fy)
Clinical Features of HDFN:
Severe: intrauterine death from hydrops fetalis (extremely anemic newborn with generalized edema and CHF)
Moderate:
o Severe anemia
o Hepatosplenomegaly
o Increased unconjugated bilirubin

If increased >20mg/dl it can cause KERNICTERUS (deposition of UCB in basal ganglia)

Occurs ONLY AFTER birth, because in utero the mother’s liver conjugates the UCB for the
fetus (protective)
Laboratory Diagnosis:
Cord Blood Testing:
o Anemia (Hb 16g/dl; normal is >20g/dl in newborns)
o Reticulocytosis
o Increased bilirubin
o Direct Coombs test (positive for anti-D)
o Erythroblastosis fetalis (increased number of nucleated RBCs in the peripheral blood)
Mother’s Testing:
o Rh negative
o High titers of anti-D antibodies
Treatment of HDFN:
Exchange Transfusion: newborn replaces his/her blood volume with blood compatible with the mother
o Compatible Blood: always use FRESH (avoid hyperkalemia) O negative RBCs + AB plasma
o Function:

Removes antibodies

Removes bilirubin

Replaces incompatible RBCs with cells compatible with the mother’s serum (prevents further
hemolysis)
Phototherapy + Simple Transfusion: may be used to treat milder HDFN with lower levels of bilirubin
o UV light degrades bilirubin
o Simple transfusion with RBCs compatible with mother’s serum
Prevention of HDFN with Rh Immunization:
Initial Prenatal Visit:
o ABO and Rh typing
o Ab screen (for anti-D Ab)
Rh(-) Mother with No Anti-D Ab:
o 28 Weeks Gestation: RhoGam shot(300 microgram dose)
o Within 72 Hours of Delivery: if the baby is Rh+; dose is determined by amount of fetal maternal
hemorrhage

Rosette Test: Rh + test cells covered with anti-D will rosette around Rh+ cells from the fetus
in the mother’s circulation
 If Negative: give another 300 microgram dose of RhoGam
 If Positive: must perform a Kleihauer Betke quantitative test
o
o
-
-
Relative resistance to hemolysis by cells containing HbF
Allows to count the number of fetal cells

Can also do flow cytometry for HbF as alternative test
o Volume of fetomaternal hemorrhage is calculated from the above
information, allowing dose of RhoGam necessary to be calculated
Rh(-) Mother with Established Anti-D Ab:
o Determine anti-D titer every two weeks during pregnancy (correlates to severity)

>16= critical titer, and you must start planning on delivery if possible
o High titers PLUS history of previously affected baby requires earlier intervention:

Amniocentesis to measure bilirubin levels in amniotic fluid (determine severity of HDFN)
 If levels are increased:
o Begin intrauterine transfusions of the fetus with Rh negative blood
starting at WEEK 24
o Plan on delivery at 25 weeks
o Expect to do an exchange transfusion at birth
Rh Immunoglobulin (RhoGam) Administration in Other Scenarios:
o Should be given when ANY EVENT occurs that might disrupt the integrity of the placenta

Therapeutic abortion

Ectopic pregnancy

Amniocentesis

Trauma to the abdomen
NEONATAL ALLOIMMUNE THROMBOCYTOPENIA (NAIT):

Definition: thrombocytopenia of the fetus and newborn cause by platelet antigen specific IgG Abs of the mother

Mechanism:
Mother lacks a common platelet specific Ag (HPA1 or HPA5)
Sensitization occurs during pregnancy and leads to IgG Abs that can cross the placenta and cause
thrombocytopenia in the fetus (may occur during first pregnancy)

Incidence: very low because platelet specific Ags are either very common or very rare in the population

Presentation:
Fetus/newborn may have severe bleeding, leading to intracranial hemorrhage

Treatment:
Platelet transfusions with:
o Washed platelets transfused from the mother, OR
o Antigen negative platelets obtained from blood supplier
Transfusions may be given intrauterine to the fetus if necessary
Other treatments include:
o IVIg
o Steroids