Red Cell Disorders Robert E. Richard, MD, PhD Assistant Professor Division of Hematology University...

Red Cell Disorders

Robert E. Richard, MD, PhD

Assistant Professor

Division of Hematology

University of Washington School of Medicine

rrichard@u.washington.edu

faculty.washington.edu/rrichard

Objectives

• Review red blood cell disorders for which transfusions are therapeutic.

• Discuss controversial areas of transfusion therapy in red blood cell disorders.

• Understand the risks related to long term transfusion therapy (non-infectious).

Anemia is operationally defined as a reduction in one or more of the major RBC measurements:

hemoglobin concentration, hematocrit, or RBC count

Keep in mind these are all concentration measures

Definition:

…most accurately measured by obtaining a RBC mass via isotopic dilution methods!

(Please don’t order that test!)

Review red blood cell disordersMarrow Production

Two main approaches that are Two main approaches that are not mutually exclusive:not mutually exclusive:

1. Biologic or kinetic approach.Biologic or kinetic approach.

2. MorphologyMorphology..

Anemia

Production? Survival/Destruction?

The key test is the …..

?

The reticulocyte count(kinetic approach)

• Increased reticulocytes (greater than 2-3% or 100,000/mm3 total) are seen in blood loss and hemolytic processes, although up to 25% of hemolytic anemias will present with a normal reticulocyte count due to immune destruction of red cell precursors.

• Retic counts are most helpful if extremely low (<0.1%) or greater than 3% (100,000/mm3 total).

The reticulocyte count

• To be useful the reticulocyte count must be adjusted for the patient's hematocrit. Also when the hematocrit is lower reticulocytes are released earlier from the marrow so one can adjust for this phenomenon. Thus:

• Corrected retic. = Patients retic. x (Patients Hct/45) • Reticulocyte index (RPI) = corrected retic.

count/Maturation time (Maturation time = 1 for Hct=45%, 1.5 for 35%, 2 for

25%, and 2.5 for 15%.)

• Absolute reticulocyte count = retic x RBC number.

Causes of Anemia (kinetic approach)Decreased erythrocyte production

•Decreased erythropoietin production

•Inadequate marrow response to erythropoietin

Erythrocyte loss

•Hemorrhage

•Hemolysis

First, measure the size of the RBCs:First, measure the size of the RBCs:• Use of volume-sensitive automated blood cell counters, such as the Coulter counter. The red cells pass through a small aperture and generate a signal directly proportional to their volume.• Other automated counters measure red blood cell volume by means of techniques that measure refracted, diffracted, or scattered light• By calculation from an independently-measured red blood cell count and hematocrit:

MCV  (femtoliters) = 10 x HCT(percent) ÷ RBC (millions/µL)

Morphological Approach(big versus little)

Underproduction (morphological approach)

MCV>115• B12, Folate• Drugs that impair

DNA synthesis (AZT, chemo)

• MDS

MCV 100 - 115• Ditto• endocrinopathy

(hypothyroidism)• Epo• reticulocytosis

Underproduction

Normocytic• Anemia of chronic

disease• Mixed deficiencies• Renal failure

Microcytic• Iron deficiency• Thal. trait• Anemia of chronic

disease (30-40%)• sideroblastic anemias

Review red blood cell disorders

Marrow production• Thalassemias• Myelodysplasia• Myelophthisic• Aplastic anemia• Nutritional

deficiencies

Red cell destruction• Hemoglobinopathies• Enzymopathies• Membrane disorders• Autoimmune

• Acquired– Immunological– Toxins – Benzene– Drugs – methotrexate, chloramphenicol– Viruses – EBV, hepatitis

• Hereditary– Fanconi,– Diamond-Shwachman

Review red blood cell disordersMarrow Production - Aplastic Anemia

• All lineages affected.

• Most patients require red cell transfusions.

• Transplant when possible.

• Transfusions should be used selectively to avoid sensitization (no family donors!).

Review red blood cell disordersMarrow Production - Aplastic Anemia

• Preleukemia, most commonly in the elderly.

• Supportive care that involves transfusion therapy is an option.

• Poor response to growth factors

Review red blood cell disordersMarrow Production - Myelodysplasia

Barosi G. Inadequate erythropoietin response to anemia: definition and clinical relevance. Ann Hematol. 1994;68:215-223 (early review)

• Anemia associated with marrow infiltration

• “teardrops”

• Cancer, infections

• Treatment is aimed at the underlying disease

• Supportive transfusions as needed.

Review red blood cell disordersMarrow Production - Myelophthisic

• Elevated reticulocyte count

• Mechanical

• Autoimmune

• Drug

• Congenital

Review red blood cell disordersRed cell destruction

Hemolytic AnemiasHemolytic Anemias

Hemolytic anemias are either acquired or congenital. The laboratory signs of hemolytic anemias include:

1. Increased LDH (LDH1) - sensitive but not specific. 2. Increased indirect bilirubin - sensitive but not specific. 3. Increased reticulocyte count - specific but not sensitive 4. Decreased haptoglobin - specific but not sensitive. 5. Urine hemosiderin - specific but not sensitive.

The indirect bilirubin is proportional to the hematocrit, so with a hematocrit of 45% the upper limit of normal is 1.00 mg/dl and with a hematocrit of 22.5% the upper limit of normal for the indirect bilirubin is 0.5mg/dl. Since tests for hemolysis suffer from a lack of sensitivity and specificity, one needs a high index of suspicion for this type of anemia.

• Hereditary spherocytosis

• Hereditary elliptocytosis

• Hereditary pyropoikilocytosis

• Southeast Asian ovalocytosis

Review red blood cell disordersRed cell destruction – membrane disorders

Review red blood cell disordersRed cell destruction – membrane disorders

• G6PD deficiency

• Pyruvate kinase deficiency

• Other very rare deficiencies

Review red blood cell disordersRed cell destruction – enzymopathies

Sickle Cell Anemia

• Single base pair mutation results in a single amino acid change.

• Under low oxygen, Hgb becomes insoluble forming long polymers

• This leads to membrane changes (“sickling”) and vasoocclusion

Sickle Cell Mutation

+O2

-O2

+O2

-O2

5'

3'Chromosome 16

5' 3'Chromosome 11 G A

CCT GAG GAG

-Pro-Glu-Glu-5 6 7

CCT GTG GAG

-Pro-Val-Glu-5 6 7

A S

Normal (HbA) Abnormal (HbS)

*

Red Blood Cells from Sickle Cell Anemia

OXY-STATE DEOXY-STATE

• Deoxygenation of SS erythrocytes leads to intracellular hemoglobin polymerization, loss of deformability and changes in cell morphology.

Deoxyhemoglobin S Polymer Structure

A) Deoxyhemoglobin S 14-stranded polymer (electron micrograph)

D) Charge and size prevent 6 Glu from binding.

C) Hydrophobic pocket for 6 Val

B) Paired strands of deoxyhemoglobin S (crystal structure)

Dykes, Nature 1978; JMB 1979Crepeau, PNAS 1981 Wishner, JMB 1975

Transfusion in Sickle Cell(Controversy!)

• Used correctly, transfusion can prevent organ damage and save the lives of sickle cell disease patients.

• Used unwisely, transfusion therapy can result in serious complications.

http://www.nhlbi.nih.gov/health/prof/blood/sickle/index.htm

• Simple transfusion – give blood • Partial exchange transfusion - remove

blood and give blood• Erythrocytapheresis – use apheresis to

maximize blood exchange

• When to use each method?

Transfusion in Sickle Cell(Controversy!)

• In severely anemic patients, simple transfusions should be used.

• Common causes of acute anemia: • acute splenic sequestration• transient red cell aplasia • Hyperhemolysis (infection, acute chest

syndrome, malaria).• If the patient is stable and the

reticulocyte count high, transfusions can (and should) be deferred.

Transfusion in Sickle Cell

• In general, patients should be transfused if there is sufficient physiological derangement to result in heart failure, dyspnea, hypotension, or marked fatigue.

• Tends to occur during an acute illness or when hemoglobin falls under 5 g/dL.

Transfusion in Sickle Cell

• Except in severe anemia, exchange transfusion offers many benefits and is our first choice

• Phenotypically matched, leukodepleted packed cells are the blood product of choice.

• A posttransfusion hematocrit of 36 percent or less is recommended.

• Avoid hyperviscosity, which is dangerous to sickle cell patients.

Transfusion in Sickle Cell(exchange transfusion)

Exchange transfusion:1. Bleed one unit (500 ml), infuse 500 ml of saline

2. Bleed a second unit and infuse two units.

3. Repeat. If the patient has a large blood mass, do it again.

Transfusion in Sickle Cell(exchange transfusion)

• A comprehensive transfusion protocol should include accurate records of the patient’s red cell phenotype, alloimmunization history, number of units received, serial Hb S percentages, and results of monitoring for infectious diseases and iron overload.

• Transfusions are used to raise the oxygen-carrying capacity of blood and decrease the proportion of sickle red cells.

Transfusion in Sickle Cell(exchange transfusion)

• Transfusions usually fall into two categories:

episodic, acute transfusions to stabilize or reverse complications.

long-term, prophylactic transfusions to prevent future complications.

Transfusion in Sickle Cell(exchange transfusion)

• episodic, acute transfusions to stabilize or reverse complications.

Limited studies have shown that aggressive transfusion (get Hgb S < 30%) may help in sudden severe illness.

May be useful before general anesthesia.

Vichinsky et al., NEJM 1995

Transfusion in Sickle Cell(exchange transfusion)

– Stroke– Chronic debilitating pain– Pulmonary hypertension– Setting of renal failure and heart failure

Transfusion in Sickle Cell(chronic transfusion therapy)

Controversial uses:– Prior to contast media exposure– Sub-clinical neurological damage– Priapism– Leg Ulcers– Pregnancy

Transfusion in Sickle Cell(chronic transfusion therapy)

Inappropriate uses of transfusion:– Chronic steady-state anemia– Uncomplicated pain episodes– Infection– Minor surgery– Uncomplicated pregnancies– Aseptoic necrosis

Transfusion in Sickle Cell

Thalassemias

• Genetic defect in hemoglobin synthesis synthesis of one of the 2 globin chains ( or )

– Imbalance of globin chain synthesis leads to depression of hemoglobin production and precipitation of excess globin (toxic)

– “Ineffective erythropoiesis”

– Ranges in severity from asymptomatic to incompatible with life (hydrops fetalis)

– Found in people of African, Asian, and Mediterranean heritage

• Dx:– Smear: microcytic/hypochromic, misshapen RBCs -thal will have an abnormal Hgb electrophoresis

(HbA2, HbF)

– The more severe -thal syndromes can have HbH inclusions in RBCs

– Fe stores are usually elevated

Thalassemias

Thalassemias

• The only treatments are stem cell transplant and simple transfusion.

• Chelation therapy to avoid iron overload has to be started early.

Iron overload and chelation

• Can occur in any patient requiring chronic transfusion therapy or in hemochromatosis.

• Liver biopsy is the most accurate test though MRI is being investigated.

• Ferritin is a good starting test.• 120 cc of red cells/kg of body weight is an

approximate point at which to think about iron overload

• Chelator, deferoxamine– 25 mg/kg sq per day over 8 hours.– Supplementation with vitamin C may aid

excretion.– Otooxicity, eye toxicity, allergic reactions.– Discontinue during an infection.

• Oral chelators are in development.

Iron overload and chelation

Conclusions

• Transfuse for any severe anemia with physiologic compromise.

• Decide early whether transfusion will be rare or part of therapy.

• Avoid long-term complications by working with your blood bank and using chelation theraoy.

SELF (9 frozen pints of artists blood, frozen in sculpture)

Mark Quinn