The literal definition of anemia is very simple and involves a low hemoglobin value shown on a CBC. On the same CBC test, there is also another value known as the mean corpuscular volume(MCV) that is very useful for the workup of anemias. Based on these two, more labs will be ordered separately which is discussed below.
Pathophysiology and etiologies
When hemoglobin decreases, this is recognized by the kidneys which release erythropoietin (EPO) in order to signal the bone marrow to ramp up red blood cell production.
Picture 1. Red bone marrow plays a role in hematopoiesis. In children (left) most of the skeleton has red bone marrow while in adults (right) it is mostly the axial skeleton
Just like most hematological deficiencies, there are 2 ways to get anemia:
- Excessive destruction
- Hemolysis or hemorrhage
- Hemoglobin levels fall, EPO increases
- Bone marrow will go into overproduction = start to release immature red blood cells
- Reticulocytosis = proportion of reticulocytes (reticulocyte index) greater than 2%
- Insufficient production
- Reticulocytes = <2%
|Types||Microcytic = MCV<80||Normocytic = MCV between 80-100||Macrocytic = MCV>100|
|Labs||Reticulocyte index < 2%||Production||Destruction||Reticulocyte index > 2%|
|Reticulocyte index < 2%||Reticulocyte index > 2%|
|Etiology||Iron deficiency = slow bleeds||Anemia of chronic inflammatory disease (due to IL6 and hepcidin)||Thalassemia||Sideroblastic||
Chronic kidney disease
Nutritional deficiency = B12 and Folate
Elevated total bilirubin and indirect bilirubin
Bilirubin levels normal
|Hypersegmented neutrophils = megaloblastic anemia = DNA problems||Elevated LFTs|
Total iron-binding capacity (TIBC)
|Bone marrow biopsy||Blood smear|
|Treatment||Iron supplementation or other||Find the cause||
Find the source of the bleed
Stop the bleed
|Supplementation or other|
When and if to transfuse
Normal hemoglobin levels are generally levels above 140 g/L. There are a number of factors that go into whether or not a patient needs to be transfused, however, make sure all the necessary lab work has been ordered before the transfusion, to get accurate results. Let's look at a few of them below:
- >100 g/L
- The patient should not be experiencing any symptoms related to anemia
- Between 70 g/L and 100 g/L
- Treat if symptomatic
- No benefit to transfusing past 70 g/L in healthy patients
- Patients who have generally poor health might require a transfusion >70 to be asymptomatic
- <70 g/L
Besides just looking at raw numbers, another factor that matters is the rate of hemoglobin drop. For instance, sickle cell disease patients often have hemoglobin around 60-70 g/L while remaining asymptomatic and will not require a transfusion. Someone with an acute bleed dropping from 140 to 90 g/L will be very short of breath and light-headed and will require a transfusion.
In general, 1 unit of packed red blood cells (PRBCs) should increase the hemoglobin by 10 g/L.
All information provided on this website is for educational purposes and does not constitute any medical advice. Please speak to you doctor before changing your diet, activity or medications.