245. Approach to Anemias

Question 1

How does reticulocyte count help you differentiate types of anemia?

How long do RBCs typically circulate in blood?

Answer 1

High reticulocyte count + anemia = adequate bone marrow response

• bleeding
• hemolytic anemia

Low reticulocyte count + anemia = inadequate bone marrow response

• aplastic anemia
• iron deficiency

RBC circulation: 110-120 days

Question 2

How is the rate of RBC production controlled? What are the steps?

Answer 2

Erythropoietin (EPO): released by kidney in response to low oxygen tension in blood

EPO causes increased RBC production in bone marrow

Low oxygen tension = increased production of HIF (hypoxia-induced transcription factor) = upregulates EPO production

Question 3

What is the definition of anemia?

What times can the typical assumption of anemia not hold true?

Answer 3

Anemia: decrease in concentration of RBC in circulating blood; key: reduction in absolute number/mass of circulating RBCs (measured by Hb, HCT, RBC count, MCV)

Assumption of anemia = low RBC concentration does not hold true when:

• decreased plasma volume (dehydration, V/D, over-diuresis, severe burns artificially raise RBC conc)
• increase plasma volume (pregnancy, CHF, edema artificially lower RBC conc)
• acute blood loss/hemorrhage may give falsely normal or high Hgb/HCT levels due to rapid loss of BOTH RBC and plasma!

Question 4

What is the FICK equation?

How does the body compensate in anemia?

Answer 4

O2 delivery = Blood flow X Hgb Conc X (Arterial O2 Saturation - Venous O2 saturation)

Compensation

• increase CO
• increase production of EPO
• increase in 2,3-DPG (decrease affinity of Hgb for O2 - help deliver O2 to tissue)

Question 5

What are the sx and physical exam findings of anemia?

Answer 5

Signs of hypoxia

• fatigue/decreased exercise tolerance
• lightheadedness, dizziness
• SoB, palpitations, cold intolerance

PE

• pallor of skin and mucosal surfaces (conjunctiva) due to preferential flow to vital organs
• tachycardia, wide pulse pressure, hypotension, systolic flow murmur
• orthostatic hypotension

Question 6

What is the KINETIC approach to causes of anemia?

Answer 6

1. Decrease in RBC production
   - Nutritional: deficient in Iron, B12, folate
   - Suppression of bone marrow: drugs (chemotx), radiation
   - Hormonal: low EPO (kidney disease), hypothyroid
   - Primary bone marrow disorder (aplastic anemia, myelodysplastic syndrome)
   - Chronic inflammatory conditions
2. Increase RBC destruction
   - Acquired Hemolytic Anemia: Autoimmune hemolysis (Coomb’s positive hemolytic anemia - cold IgM Ab mediated RBC destruction), Microangiopathic Hemolysis (DIC, TTP), Infection (Babesiosis, malaria)
   - Inherited: Membrane Defects (Elliptocytosis, spherocytosis), Hemoglobinopathies (Thalassemia, Sickle Cell), Enzyme Deficiency (G6PD deficiency)
3. Blood Loss
   - menorrhagia
   - occult GI blood losses
   - trauma

Question 7

What is the MORPHOLOGIC approach to causes of anemia?

Answer 7

1. Microcytic anemia (MCV < 80)
   - less iron available: iron deficiency, inflammation, Cu deficiency
   - sideroblastic anemia
   - less globin synthesis: hemoglobinopathies (will have high RBC count)
   - less heme synthesis (LEAD poisoning)
2. Macrocytic anemia (MCV > 100)
   - Reticulocytosis
   - Abnormal RBC maturation: myelodysplastic syndrome, leukemias
   - Abnormal nucleic acid metabolism: B12/folate deficiency
3. Normocytic anemia (MCV 80 - 100)
   - primary bone failure (aplastic anemia)
   - chronic inflammatory conditions
   - blood loss

Question 8

What is the Mentzer Index?

Answer 8

Relationship between RBC and MCV
- help differentiate between thalassemia (high RBC count) and other causes of microcytosis (low RBC count)

index: MCV/RBC count
Index < 13 = thalassemia more likely than iron deficiency

Question 9

If RBC parameters are normal, the next step is to:

Answer 9

LOOK AT THE PERIPHERAL BLOOD SMEAR