Hemolytic Anemias Flashcards
Hemolysis:
means premature destruction of circulating red cells
– Normal red cell survival in circulation is 120 days (3 months)
hemolytic anemia:
is when there is hemolysis and bone marrow cannot compensate
compensated hemolytic anemia:
– Can increase red cell production by 7 times
(reticulocytosis)
– Results in increased erythropoiesis in bone marrow (bone marrow erythroid hyperplasia)
What are the 5 categories of hemolytic diseases?
– Membrane defects (congenital or acquired)
– Metabolic defects (congenital or acquired)
– Hemoglobin Defects (congenital; RARELY acquired)
– Mechanical destruction(congenital or acquired) – Immune Destruction (congenital or acquired)
intravascular hemolysis:
lysis of red cells in the VASCULAR TREE
extravascular hemolysis:
– Phagocytic destruction of red cells by reticuloendothelial (RE) system, i.e. macrophages
– Occurs in spleen, liver, bone marrow
what is released in intravascular hemolysis?
cells destroyed in circulation release LDH and Hgb
the FREE hgb binds to HAPTOGLOBIN
the hemoglobin-haptoglobin complex is CLEARED by hepatocytes
What happens when there is poorly compensated intravascular hemolysis?
serum haptoglobin level goes DOWN (more bound to free hgb)
LDH level goes up (more cells destroyed)
Products of Hgb breakdown go UP
what happens to lab markers in SEVERE intravascular hemolysis?
haptoglobin?
LDH?
- Haptoglobin becomes saturated (very low haptoglobin) – bound to Hgb
- LDH level gets very high
What is hemoglobinemia?
Free Hgb presen in teh blood
(and Hgbx3 – HCT can be > +2)
What is hemoglobinuria?
alpha-beta dimers can be filtered by glomerulus and pass in urine
what is hemosiderinuria:
renal tubular cells take up and metabolize the alpha-beta dimers to form hemosiderin granules
what percent of RBCs are destroyed every day extravascularly in normal adults?
11%!
– Senescent RBCs, abnormally shaped RBCs
– Accelerated in pathologic hemolysis
• intrinsic or extrinsic RBC abnormalities
Where does extravascular hemolysis occur?
Red cells degraded by macrophages in RE system
– spleen, liver, bone marrow
What happens in pathologic extravascular hemolysis?
some free hgb spills into circulation
– Decreased haptoglogin
– Free hemoglobin in severe cases
How is Hgb broken down?
Hgb is broken down to Fe, heme and globin
Fe is recycled/stored in…
RE cells as ferritin or hemosiderin
Heme is broken down to…
bilibrubin
• Transported to liver by albumin
• Conjugated in liver, excreted as bile
• Converted to urobilinogen, urobilin and stercobilinogen by bacterial flora; eliminated in feces
• Some urobilinogen is reabsorbed and excreted in urine
Globin is broken down into…
AA
What are consequences of chronic hemolytic anemia?
- increased indirect (unconj) bilirubin
- erythroid hyperplasia of bone marrow
- splenomegaly
- Fe overload
What hematologic changes are associated with hemolytic anemias?
• Usually normochromic normocytic
– May be macrocytic due to reticulocytosis and/or folate
deficiency
• RBC morphology
– Poikilocytosis (red cell shaped changes) can give clues both to the presence of hemolysis and the cause of hemolysis (if someone notices it on the blood smear)
• Reticulocytosis
– Proportional to severity of anemia and bone marrow ability to
respond
• Erythroblastemia (circulating nucleated red cells)
• Bone marrow changes
– Hypercellular: erythroid hyperplasia – Iron overload
• Chronic hemolytic anemia- aplastic crisis
– Erythroid aplasia with severe exacerbation of anemia – Parvovirus B19 erythroid maturational arrest
reticulocyte ?
polychromatophili red cell that contains RNA
reticulocyte count?
Percentage or absolute number of reticulocytes can be used to assess bone marrow response to blood loss
caveats re reticulocyte count?
– Can be increased with hemorrhage or hemolysis, or erythropoietin therapy, or bone marrow recovery after toxic, nutritional or other insult!
– Don t forget to correct a % reticulocyte count for degree of anemia!
– A reticulocyte response may not occur for up to 72 hours after hemolysis becomes severe enough to cause anemia!
If the bone marrow is fully functional, an increase in erythropoietin caused by acute blood loss or hemolysis will result in increased numbers of circulating reticulocytes within approximately ____ hours
72
Why should we correct %reticulocytes?
If the box on the left represents the normal number and the normal percentage of reticulocytes in a measured volume of blood, the box on the right has a “normal” number of reticulocytes
for volume but the percentage is very high
RPI <2
failed erythropiesis
RPI >3
marrow hyperproliferration or APPROPRIATE response
when counted by an automated machine, how are reticulocytes reported?
as an absolute number in a measured volume of total red cells
what is a leukoerythroblastic reaction and what does it indicate?
• Nucleated red cells and immature granulocytes in blood reported on the leukocyte differential count • Indicates severe marrow stress – Hemolysis – Hemorrhage – Sepsis – Marrow infiltration • Carcinoma • Leukemia/lymphoma • Infection, e.g. granulomas – Early newborn period (physiologic)
what is haptoglobin?
• Produced by liver
• Binds to free hemoglobin so is decreased or absent
in hemolysis
low haptoglbobin is seen in?
– advanced liver disease
– recent massive transfusion
– genetic variant
– Megaloblastic anemias (including B12 or folate deficiency!)
how is haptoglobin an acute phased reactant?
– increased 3-4 x in inflammation, infection, tissue necrosis
(e.g. pneumonia, myocardial infarction)
– Inflammation or infection may mask the expected decrease in haptoglobin caused by hemolysis!
is haptoglobin sensitive or specific for hemolysis?
NOOO!
what is LDH?
Increases due to red cell destruction with leakage of enzymes, including LDH
why is LDH1 more useful than LDH?
LDH is a Nonspecific test
– Increased due to any type of tissue damage
– LDH isoenzymes more useful; LDH1 found predominantly in red cells and myocardium