Classification of Anemia
Basic Lab Workup: CBC with indices, examine smear,
platelet count, ferritin level, TSH, BUN/Cr, AST, LDH, indirect bilirubin. Check
reticulocyte count and haptoglobin if hemolysis is suspected strongly.
First, use the MCV (mean corpuscular volume) to determine
whether the anemia is microcytic, normocytic, or macrocytic.
top of page
Causes: The most common cause is iron deficiency anemia.
Step 1: Check for a Low Ferritin:: The definitive test for iron deficiency anemia
is measurement of the serum ferritin level. An iron deficiency
anemia in the presence of a clearly normal or elevated ferritin is very
unlikely. The serum iron, total iron binding capacity and transferrin
saturation cannot distinguish iron deficiency from anemia of chronic
disease. Bone marrow aspirate when negative for iron may be helpful, but
an empiric trial of iron replacement can be a more useful way to deal with
equivocal cases. Increased RDW (red cell distribution width) favors iron
deficiency. Microcytic anemia with increased red blood cell count is
most often Thalassemia trait (MCV/RBC < 13 usually indicates
thalassemia, MCV/RBC >13 is usually iron deficiency).
Microcytosis without anemia is possible in thalassemia trait and in
polycythemia associated with iron deficiency. Anisocytosis and poikilocytosis
are usually present in iron deficiency anemia. In severe cases cigar
shaped cells or elliptocytes may be present. Polychromasia, basophilic
stippling, and target cells are not typical of iron deficiency. Reactive
thrombocytosis is common in iron deficiency anemia.
Evaluation of Microcytic Anemia with Normal Ferritin: Ask yourself
whether the microcytosis is old or new ? If it is old, then it may be a
congenital disorder such as thalassemia. If it is new, then it may be an
acquired non-thalassemic microcytic anemia.
Thalassemic Syndromes: 97% of normal adult
hemoglobin (hemoglobin A) is made up of equal quantities of alpha and beta
globin chains. Thalassemia is defined as a decreased production of
either of the these two globin chains (e.g., alpha-thalassemia and
beta-thalassemia) or a structurally abnormal globin chain (e.g., hemoglobin
E). The abnormal globin causes microcytosis and an abnormal electrophoresis
pattern. The test of choice for investigating thalassemia is
hemoglobin electrophoresis, but remember it does not always detect
thalassemia (see below).
Alpha-Thalassemia: alpha-globin is controlled by 4
genes (2/haploid chromosome). Consider family history and ethnic origin.
Mutation in 4/4 genes causes hydrops fetalis
Mutation in 3/4 genes causes beta chains to form tetramers of hemoglobin
H with severe microcytic anemia. Electrophoresis is abnormal.
Mutation in 2/4 genes causes microcytosis and mild anemia, called
alpha-thalassemia trait. Electrophoresis is normal. PCR and
southern blot tests can show thalassemia trait.
Mutation in 1/4 genes creates a silent carrier with no
microcytosis or anemia.
Beta- Thalassemia: beta-globin is controlled by 2
genes (1/haploid chromosome).
Mutation of 1/2 genes causes beta-thalassemia
trait. Note that in this condition with normal ferritin levels
Hemoglobin A2 will generally go from a normal value of 2% up to 3-6%.
However, if the patient has low iron, then this may not occur. A normal
Hemoglobin A2 level must be accompanied by a normal ferritin level to be
sure you are not accidentally missing a beta-thalassemia trait condition
in which iron is lacking causing a low Hemoglobin A2.
Mutation of 2/2 genes causes symptomatic beta thalassemia.
Electrophoresis will show mostly Hemoglobin F (alpha2,gamma2). A slight
increase in Hemoglobin F may be seen in beta thalassemia trait and
compound heterozygotes. Therefore, electrophoresis will generally be
adequate for evaluating beta-thalassemia with genetic testing only
needed on occasion.
Structurally Abnormal Globin Chain Thalassemia: some
structural hemoglobinopathies can cause a microcytic phenotype due to
decreased globin production. The three examples below can be identified by
Ex: Hemoglobin E, structural
hemoglobinopathy common in SE Asia due to RNA splice mutation.
Ex: Hemoglobin Lepore, due to fusion of a delta and beta-globin
Ex: Hemoglobin Constant Spring, due to a stop codon
mutation resulting in a longer unstable globin messenger RNA.
Non-Thalassemic Conditions Associated with Microcytosis
other than Iron Deficiency: the differential diagnosis of this
includes: Anemia of Chronic Disease and Hereditary or Acquired
Anemia of Chronic Disease: this anemia is usually
normocytic. However, some systemic diseases can result in a microcytic
process, e.g., rheumatoid arthritis, polymyalgia rheumatica, diabetes
mellitus, connective tissue diseases, chronic infection, Hodgkin's
Lymphoma (HL), Castleman disease (CD), renal cell carcinoma (RCC), and
myelofibrosis with myeloid metaplasia (MMM). The first five cause mild
microcytosis, with normal RDW, and normal smear. Diagnosis is made
clinically. Microcytic anemia in the last three is often associated with
systemic symptoms: fever, constitutional symptoms, pruritus (HL),
lymphadenopathy (HL,CD), monoclonal gammopathy (CD), hematuria (RCC),
splenomegaly (MMM, HL, CD), or leukoerythroblastosis (nucleated red
cells on peripheral smear (MMM).
Anemia (MCV 80-100fL)
top of page
Step 1: Rule out readily treatable causes.
Nutritional Anemia: may be related to both iron
deficiency and/or B12/folate deficiency. First, determine a ferritin
and B12/folate levels.
Anemia of Renal Insufficiency:
there will be a normal blood smear with an inappropriately elevated
erythropoietin level. Can be severe when Cr>3 mg/dL, mild to moderate
when Cr 1.5-3.0 mg/dL. Consider hemolysis.
Anemia: look for evidence of red cell destruction with elevated serum
LDH; increased red cell catabolism with increased indirect bilirubin,
decreased level of haptoglobin (serum protein that clears free hemoglobin);
and increased reticulocytes demonstrating increased bone marrow regenerative
action. Therefore, when hemolysis is suspected check: reticulocyte count,
indirect bilirubin, serum LDH, and haptoglobin. None of these tests
are specific. Urinary hemosiderin is absent in extravascular hemolysis, but
present in intravascular hemolysis
Extravascular hemolytic processes: red cell
intrinsic and immune mediated hemolytic anemia.
Intravascular hemolytic processes: microangiopathic processes,
infection associated, and chemical-induced hemolytic anemia.
Diagnosis of Hemolytic Anemia:
Membranopathies (e.g., hereditary spherocytosis-
Enzymopathies (e.g., G6PD deficiency- interacts with sulfa)
Hemoglobinopathy (e.g., sickle cell disease)
Red Cell Extrinsic causes:
Microangiopathic (e.g., TTP/HUS)
Related (e.g., falciparum malaria)
Agent (e.g., spider venom)
Step 2: Normocytic Anemia not associated with Nutritional
deficiency, Renal Insufficiency, or Hemolysis will include: Anemia of Chronic
Disease or Primary Bone Marrow disorder or other causes.
Anemia of Chronic Disease: usually normocytic, but
can be microcytic. Current theory is that it is caused by a
cytokine-mediated inhibition of red cell production or erythropoietin
production or function. Often associated with diabetes mellitus, connective
tissue disease, chronic infections, and malignancy. Serum iron and
transferrin saturation may be low in these conditions, therefore
always check a ferritin level, this is the best test to differentiate
iron deficiency from anemia of chronic disease.
to a Primary Bone Marrow Disorder: check the peripheral smear in these
conditions. Consider a bone marrow biopsy, especially in younger patients
with histories of chemotherapy or abnormal blood smears.
Myelodysplastic Syndrome: look for an increased
RDW, oval macrocytes, hyposegmented neutrophils, or monocytosis.
Bone Marrow Infiltration: think about metastatic cancer and myeloid
metaplasia. Look for nucleated RBC's, immature myeloid cells.
Rouleaux may form in multiple myeloma. Consider lymphoma,
Aplastic Anemia: look for severe anemia with low reticulocyte
count. Look for platelet and white cell abnormalities or low counts which
are common in many bone marrow effecting conditions. Consider pure
red cell aplasia, congenital, idiopathic, paroxysmal nocturnal
hemoglobinuria, Fanconi anemia.
Acute Blood Loss
Anemia (MCV>100 fL)
top of page
Step 1: Rule out drugs that cause macrocytosis.
Consider: alcohol, hydroxyurea, methotrexate,
trimethoprim, zidovidine, 5-fluorouracil. Hydroxyurea can cause
Step 2: Rule out Nutritional Causes of Macrocytic Anemia.
Check for vitamin B12 and folate deficiencies with a B12
level, methylmalonic acid level, folate level, red cell folate level, and
homocysteine level. Folate levels can be altered by recent
dietary intake. Red cell folate levels can be imprecise.
Homocysteine levels will be high in folate deficiency due to impaired
folate dependent conversion of homocysteine to methionine.
Therefore, a normal homocysteine level is good evidence against folate
deficiency. B12 levels may be falsely low during pregnancy, in the
elderly, and when white cell counts are low. The methylmalonic acid level
is a more sensitive and specific test for B12 deficiency. If the
methylmalonic acid level is normal then B12 deficiency is very
unlikely. B12 is a cofactor for converting methylmalonyl coenzyme A
to succinyl coenzyme A, so if methylmalonic acid levels are high then B12
may be low. In this setting, renal insufficiency and certain inborn
errors of metabolism can cause an increased methylmalonic acid level.
a diagnosis of B12 deficiency is made, then you must search for a cause
for it. The first test is a screen for intrinsic factor
antibodies. If it is positive you have diagnosed pernicious
anemia and begin replacement therapy. If it is negative then a Schilling's
test can be performed to help differentiate pernicious anemia from
intestinal malabsorptive disorders. Malabsorptive disorders may include:
tropical sprue, celiac sprue, inflammatory bowel disease, amyloidosis,
intestinal lymphoma, pancreatic insufficiency (creates a lack of pepsin
needed to release food bound B12), bacterial overgrowth, and gastric
atrophy (fail to release acid to allow release of food bound B12).
Step 3: Evaluate for Non-Drug Induced, Non-Nutritional
First, classify whether the macrocytosis is mild (MCV
100-110 fL) or marked (>110).
Marked Macrocytosis: when this is not due
to nutritional deficiency it is nearly always due to a primary bone
marrow disease such as: Myelodysplastic syndrome, Aplastic anemia,
pure red cell aplasia, or large granular lymphocyte disorder.
A bone marrow biopsy is indicated if it will make a difference in
Mild Macrocytosis: First, study the
peripheral smear. Polychromasia (indicates reticulocytosis)
suggests hemolysis. Red cells appearing round or as target cells
suggests liver disease or hypothyroidism.
top of page
Performed in two stages, but stage two is performed only
if stage 1 is abnormal.
In stage 1, patients receives, 1 mg
B12 IM to saturate B12 binding proteins and 1 mcg of radiolabeled crystalline
B12 orally. A 24 hour urine collection is started. This urine is checked
for radioactivity. If >7% of the ingested load of B12 is found in the
urine then the patient has no problem absorbing crystalline B12.
A normal stage 1 rules out pernicious
anemia. Malabsorption may still be a problem. Elderly people
may lack gastric acid due to gastric atrophy or pepsin needed to release
food bound B12. Abnormal stage 1 results suggest either
pernicious anemia or malabsorption. Rarely, bacterial overgrowth or
pancreatic insufficiency may cause abnormal stage 1 results.
In stage 2, patients with abnormal stage 1 results are
given intrinsic factor (60 mg) along with oral B12. If the B12 is
absorbed adequately then pernicious anemia is present. If it does
not correct, then you cannot absolutely rule out pernicious anemia because
the gut epithelium may be abnormal preventing absorption and mimicking
malabsorption. Therefore the best time to do a Schilling's test is after
two weeks of treatment with B12 to assure the absorptive surfaces are
top of page
Iron Deficiency anemia
Antacid Rx or hi gastric pH
Excess Dietary Bran, Tannins, Phytates or Starch
Competition for other metals (e.g. copper or lead)
Loss or dysfunction of eneterocytes
Short Bowel Syndrome or bowel resection
Inflammatory Bowel Disease
Intrinsic Enterocyte decrease
Gastrointestinal Blood Loss
Peptic Ulcer Disease
Milk enteropathy of early childhood
Inflammatory Bowel Disease
Genitourinary Blood Loss
Pulmonary Blood Loss
Other Blood Loss
Poor dietary intake
Non-thalassemic Conditions associated with
Anemia of Chronic Disease
Connective Tissue Diseases
Renal Cell Carcinoma
Myelofibrosis with Myeloid Metaplasia
Blood Loss, Acute
Iron Deficiency Anemia
Anemia of Renal Insufficiency
Red Cell Intrinsic causes
Enzymopathies (Annals Int Med, 1985;
Hexose Monophosphate Shunt deficiencies
Pyruvate Kinase Deficiency
Glucose Isomerase Deficiency
Phosphoglycerate Kinase Deficiency
Lactate Dehydrogenase Deficiency
2,3-DiPhosphoglycerate mutase and Phosphatase Deficiency
Adenylate Cyclase Enzymopathy
Adenosine Deaminase Enzymopathy
Pyrimidine Nucleotidase Deficiency
Sickle Cell Disease
Red Cell Extrinsic causes
Immediate Transfusion Rx
Delayed Transfusion Rx
Anemia of Chronic Disease
Bone Marrow Disorder
Intrinsic to hematopoietic stem cells
Pure Red Cell Aplasia
Other Myeloid Process
Bone Marrow Infiltrating Process
Hydroxyurea, methotrexate, zidovidine,
Large Granular Lymphocyte Disorder
Alcohol or Liver Disease
Hemolytic Anemia- reticulocytosis
Cold agglutinins present
Teferri,A, Anemia in Adults: A contemporary
Approach to Diagnosis. Mayo Clinic Proceedings.
2003;78:1274-80. Plagiarized heavily for
this page !! Thanks.
Andrews,NC, Disorders of Iron Metabolism. NEJM. 1999;341:1986-94.
Valentine,WN,et al, Hemolytic Anemias and Erythrocyte Enzymopathies. Annals
Int Med. 1985;103:245-57.