Approach to anemia

Definitive guide Posted by Ahmad Azizov on October 11, 2020


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% 
Table 1. Causes and workup of anemias
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




DNA problems

Nutritional deficiency = B12 and Folate 


ETOH abuse

More labs

Low Fe

Low Ferritin

Low Fe

High Ferritin

Normal Fe

Normal Ferritin

Elevated Fe


Elevated LDH 

Decreased haptoglobin 

Elevated total bilirubin and indirect bilirubin

LDH normal 

Haptoglobin normal 

Bilirubin levels normal

Hypersegmented neutrophils = megaloblastic anemia = DNA problems Elevated LFTs 

Fe levels 


Total iron-binding capacity (TIBC)

% saturation

Bone marrow biopsy Blood smear    
Treatment Iron supplementation or other   Find the cause

Find the source of the bleed

Stop the bleed

Transfuse blood

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
    • Transfuse 

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. 

Written by
Ahmad Azizov Member since April 2020
Interested in vascular surgery, surgery, endovascular procedure

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