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Causes of Anemia: decreased Hb, decreased Hct, decreased RBCs, decreased…
Causes of Anemia:
decreased Hb, decreased Hct, decreased RBCs, decreased O2 carrying capacity --> tissue hypoxia, cellular injury, and death
Decreased RBC production:
decreased erythropoiesis, decreased reticulocyte count
Inability to use iron
: ACI and IRIDA are characterized by inappropriate hepcidin levels leading to decreased absorption and retention of Fe.
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Anemia of chronic disease
(inflammation): most common form of anemia among hospitalized and chronically ill patients. Usually mild to moderate anemia (Hb 8-11 g/dl). Normo/microcytic. Normal or low retic count.
Common conditions:
chronic infection, connective tissue disorders (ex. Lupus), cancer and lymphoma, major trauma, ulcerative colitis, regional enteritis.
Pathogenesis:
Inflammation stimulates IL-6 production, which in turn promotes hepatic hepcidin expression. Fe recycling becomes inefficient and iron is retained in macrophages (hence increase in ferritin levels). Transferrin saturation decreases and erythropoiesis becomes iron restricted.
Iron-resistant iron deficiency anemia
(IRIDA): Rare autosomal recessive disorder. Lifelong low serum iron and transferrin saturation. Impaired iron absorption and utilization that is unresponsive to oral iron. Mutations in gene for protein that helps decrease transcription of hepcidin.
Other causes of decreased RBC production
Kidney disease
Toxins
Aplastic anemia (note: PNH causes increased risk for aplastic anemia).
Folate and B12 deficiencies
Diagnostics
(a)
serum B12 < 150, total serum homocysteine >15 umol/l or methylmalonic acid > 0.4 umol/l. If serum folate > 4 ng/ml then NOT folate deficiency.
(b)
morphology: macrocytic (megaloblastic), high MCV (<100), low reticulocyte count, hypersegmented neutrophils.
If you suspect B12 or folate deficiency, check for both!
Causes of B12 deficiency
Other causes:
low stomach acid due to antacid use, bacterial overgrowth and consumption of B12, pancreatic insufficiency resulting in lack of proteases to release B12 from binding protein, surgical factors.
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Pernicious anemia:
autoimmune destruction of gastric parietal cells due to anti-IF antibodies (0.1% of general population, 1.9% of those 60+), anti-parietal cell antibodies. Often seen in association with other autoimmune diseases as well as with an increased risk of GI tract malignancy.
Causes of folate deficiency
Diet:
alcoholism, cooking/food processing, depressed patients (not eating)
Malabsoprtion:
Celiac disease, IBD, short bowel syndrome
Drugs (antifolates):
methotrexate, trimethoprim (Bactrim - often used for bladder infections).
Increased requirements:
pregnancy, lactation, chronic hemolysis, exfoliative dermatitis.
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Iron deficiency anemia (IDA)
Causes
Increased demand
Pregnancy
Rapid growth:
infancy and adolescence. Infants triple their weight in the first year of life and must accumulate ~100mg of iron during the first year to keep up with the hemoglobin production.
Blood loss:
GI (malignancy, peptic ulcers, gastritis from NSAIDS or
H. pylori
, hookworm, Meckel's diverticuli, hemorrhoids, vascular malformations, menstrual (avg blood loss 30-40 ml, 15-20 mg Fe), childbirth, trauma, chronic hemoglobinuria (mechanical heart valve,
PNH
).
Inadequate supply
Malabsorption:
increased absorption of heme iron (15%) over non-heme iron, ascorbic acid (Vitamin C) facilitates ferrireduction. Decreased absorption due to plant iron (3%), tannins (tea, coffee), bran/fiber/Ca++, disrupted mucosa (IBD, Celiac disease, surgery), achlorhydria (gastrectomy, antacids, proton pump inhibitors).
Nutritional deficiency:
(a) young children (1-5yo) due to excessive milk intake, prolonged bottle use, picky eaters, (b) teenage girls due to poor diet, worsened by rapid growth and menstrual blood loss, (c) socioeconomic status.
Diagnostics
(a)
biochemical markers: decreased ferritin, decreased serum Fe, decreased transferrin saturation, increased TIBC, increased serum transferrin receptor, increased FEP. No iron in bone marrow aspirate.
(b)
morphology: microcytic, hypochromic RBCs (MCV < 80), occasional elliptocytes (pencil cells), high RDW.
Treatment: (1) correct deficiency and (2) address underlying problem/cause
Folate: oral folate of 400-1000 ug daily
B12: parenteral B12 - intense loading dose followed by monthly maintenance or oral B12 at 1-2 mg/day.
ACI: Erythropoietin, IV iron, RBC transfusion.
Fe:
Reticulocyte count begins to rise in 3 to 4 days, peaking in 5 to 10 days. Hb rises following elevation in retics.
(a)
oral ferrous sulfate (3-6 mg/kg/day elemental Fe [200mg for adults], treat for 2 months beyond correction of anemia to replete stores, side effects include nausea, epigastric discomfort, constipation).
(b)
slow release iron (decrease GI side effects, more expensive, may release Fe below duodenum).
(c)
parenteral iron (IM, IV) which is useful in cases of poor adherence. This option has significant side effects and risk of anaphylaxis.
Increased RBC destruction:
hemolysis, decreased RBC survival, increased erythropoiesis, marrow compensation, increased reticulocyte count
Extrinsic hemolysis
Immune hemolytic anemia
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Autoimmune hemolytic anemia (AIHA)
IgM-mediated (cold):
Mechanism
IgM antibodies to antigens on the RBC. Optimal binding occurs below 37 degrees Celsius. The IgM Ab fix complement. Complement remains bound even after IgM leaves the RBC. Complement-coated RBCs are cleared by C3b receptor-expressing Kuppfer cells in the liver.
Causes
(1) Idiopathic, (2) infection especially with EBV, mycoplasma, (3) lympoproliferative disorders.
Treatment
Avoidance of cold exposure, treat underlying disorder (if present), Rituximab (anti-CD20), plasma exchange as a temporizing measure.
IgG-mediated (warm)
Mechanism
IgG antibodies bind to antigens on the RBC (optimal binding occurs as 37 degrees Celsius. Ab-coated RBCs are cleared by Fc receptor-expressing macrophages in the spleen. Partial phagocytosis results in spherocytes.
Causes
(1) Idiopathic, (2) autoimmune disorders, (3) lymphoproliferative disorders.
Treatment
Corticosteroids, splenectomy, treat underlying disorder (if present), other immunosuppressive agents.
Diagnosis
: Direct antiglobulin test (Coombs). Patient's RBCs are washed and incubated with Coombs reagent (anti-human IgG or anti-human C3). Agglutination indicates a positive test.
Drug-induced immune hemolytic anemia
Causes
Beta-lactam Abx, NSAIDs, quinine/quinidine
Treatment
Withdrawal of causative agent.
Mechanism
Alteration of antigen: Drug (e.g. methyldopa) induces an alteration in a
Neoantigen-mediated: drug (e.g. quinine) binds to a membrane antigen and induces it to change conformation, exposing a neoantigen.
Hapten-mediated: drug (e.g. penicillin) binds directly to the RBC membrane, where it serves as the target antigen.
(2) Hemolytic uremic syndrome (HUS)
(1) Thrombotic thrombocytopenic purpura (TTP)
3) malignant hypertension
(4) vasculitis (inflammation of blood vessels)
(5) disseminated intravascular coagulation (DIC)
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Microangiopathies (MAHA)
Causes
(1) Thrombotic thrombocytopenic purpura (TTP)
(3) Malignant hypertension
(4) Vasculitis (inflammation of blood vessels)
(5) Disseminated intravascular coagulation (DIC)
(2) Hemolytic uremic syndrome (HUS)
Paroxysmal Nocturnal Hemoglobinuria (PNH)
Mechanism
RBC membranes contain glycosyl phosphatidylinositol (GPI) molecules, which anchor extracellular proteins to the RBC surface, such as CD55 and CD59 which limit complement activation of RBC surfaces. PNH is an acquired clonal disorder due to somatic mutations in
PIG-A
, which encodes an enzyme required for the synthesis of GPI. The result is intravascular hemolysis.
Treatment
Iron and folate supplementation, blood transfusion, Eculizumab (C5 terminal complement inhibitor - increased risk for meningococcal infections). Also note increased risk of VTE.
Diagnosis
Flow cytometry for CD55 and CD59 on neutrophils or monocytes (because RBCs without them will likely have already been destroyed)
Infection
Mechanism
RBC membrane injury caused by bacterial toxin. This is seen in Clostridial sepsis. A toxin produced by the bacterium (phospholipase C) destroys the RBC membrane, leading to brisk intravascular hemolysis.
Infestation of RBCs by parasites. Seen in malaria, Babesiosis - infested RBCs are removed by macrophages in the spleen.
Immune hemolysis due to antigen mimicry (mycoplasma pneumoniae, EBV, HSV).
Intrinsic hemolysis
Abnormal RBC membrane
Hereditary spherocytosis (HS)
: defect in one of several proteins that make up the RBC cytoskeleton (commonly spectrin). Abnormal RBCs have shortened lifespan. High reticulocyte count.
Morphology: spherocytes, normocytic, hyperchromic, high reticulocyte count (polychromasia).
RBC enzyme deficiency
G6PD deficiency
: most common red cell enzymopathy, X-linked, mostly males affected. Two common variants - African American males G6PD A-, and Mediterranean/Asian ancestry G6PD B.
Diagnostics: biochemical assay, best tested several months after the acute event.
Treatment: avoidance of triggers; RBC transfusion as needed for acute episodes.
Hemoglobinopathies
Thalassemia:
quantitative problem with hemoglobin synthesis due to abnormalities in synthesis of the global chains (alpha or beta).
Beta-thalassemia
: excess alpha chains resulting in damaging precipitate --> profound anemia.
Diagnostic
: microcytic RBCs, low MCV (<70), hypochromic, presence of target cells, elevated reticulocytes, normal iron, increased HbA2 +/- HbF on hemoglobin electrophoresis.
B thalassemia major (Cooley's anemia): Bo/Bo
Physical
Laboratory
History
B thalassemia intermedia:
Bo/B+, B+/B+. Occasionally nucleated RBCs.
B thalassemia minor (trait)*
: Bo/B, Hb > 10 g/dl, MCV 50-70, 5-7% HbA2.
Alpha-thalassemia
: excess B chains resulting in HbH.
Silent carrier (-a/aa)
a thalassemia trait: -a/-a OR --/aa
HbH disease: --/-a
Hydrops fetalis: --/--
Sickle Cell Disease:
mutation of glutamic acid to valine in the 6th position on the Hb beta chain. HbS molecules aggregate into needle-like structures when deoxygenated, resulting in anemia, RBC damage, and extravascular hemolysis.
Diagnosis: Normocytic, sickle cells, occasional target cells.
Signs and symptoms:
Hemolytic anemias:
jaundice (due to release of bilirubin resulting from breakdown of Hb), splenomegaly, hemoglobinuria (especially with intravascular hemolysis), gallstone disease.
G6PD deficiency:
hemolysis is usually precipitated by an acute event that induces oxidant stress: (1) acute illness, e.g. infection, (2) exposure to certain drugs or chemicals, e.g. napthalene, sulfa antibiotics (also problematic w/ folate deficiency), (3) fava bean ingestion.
IDA:
pallor, weakness, fatigue, headache, irritability, alopecia, dry/rough skin, restless leg syndrome, neurocognitive dysfunction, pagophagia, beeturia, blue sclerae, koilonychia (nails), angular stomatitis.
B12/folate deficiency
Fatigue, appetite loss, venous thrombosis
Neuropsychiatric (if untreated, irreversible): polyneuritis, ataxis/balace, combined sclerosis of spinal cord (specific to B12), neural tube defects (specific to folate) depression, blindness. Subacute combined degeneration affects brain, spinal cord, peripheral nerves -- optic neuropathy, memory loss, visual impairment, weakness, progressive sensory abnormalities, gait impairment.
oral/GI: diarrhea, cheilitis, glossitis (inflammation of the tongue)
Laboratory evaluation:
CBC, reticulocyte count, peripheral blood smear. Specific tests then based upon differential.
If decreased WBC count or platelet count, proceed with bone marrow evaluation.
If normal WBC/platelets: evaluate blood smear for size, color, and shape of RBCs. Classify by MCV - micro, normo, or macro.
Microcytic RBCs:
decreased heme synth (IDA, sideroblastic anemia, severe lead poisoning, ACI) and decreased globin synthesis (thalassemia syndromes).
Pencil cells: check iron studies for IDA
Target cells: check for a thalassemia (decreased globin synthesis).
Normocytic RBCs
Check reticulocyte count
Low retics: marrow not active and the issue is probably a bone marrow disorder or decreased EPO.
High retics: marrow is healthy and compensating for hemolysis or bleeding
All hemolysis: increased LDH, bilirubin (unconjugated), retics; intravascular hemolysis: decreased haptoglobin, increased plasma Hb, hemoglobinuria
Sickle cell anemia
Macrocytic RBCs
: B12, folate deficiencies
if MMA and homocysteine are both elevated then B12
If only homocytsteine elevated, then folate deficiency
