Iron deficiency anemia
AssessmentsIron deficiency anemia
Iron deficiency anemia
USMLE® Step 1 style questions USMLE
A 31-year-old woman comes to the clinic because of increasing fatigue and dizziness over the past several months. She started a vegan diet six months ago. Menarche occurred at age 14, and menses occur regularly every 28 days, with heavy and prolonged menstrual bleeding. Family history is non-contributory. Temperature is 36.4°C (97.5°F), pulse is 90/min, respirations are 14/min, and blood pressure is 125/79 mmHg. Physical examination shows conjunctival pallor. Laboratory investigations reveal a hemoglobin level of 10.3 g/dL. Which of the following sets of laboratory values is most likely to be present in this patient?
Iron deficiency anemia exam links
Content Reviewers:Viviana Popa, MD
Contributors:Jahnavi Narayanan, MBBS, Jung Hee Lee, MScBMC
Anemia is a condition where there’s a decrease in the number of healthy red blood cells, or RBCs, in the body.
So, iron deficiency anemia means anemia caused by a deficiency in iron.
Iron deficiency anemia is also the most common type of anemia worldwide.
If we take a close look at our red blood cells, we’ll notice that they’re loaded with millions of copies of the same exact protein called hemoglobin, which binds to oxygen and turns our blood cells into little oxygen transporters, and basically allow us to move oxygen to all the tissues in our body.
If we take an even closer look at those hemoglobin proteins, we’ll find that they’re made of four heme molecules, which have, right in the middle, iron.
This iron molecule is what binds to oxygen, so each hemoglobin molecule can bind four molecules of oxygen.
In addition, iron is also an important part of proteins like myoglobin, which delivers and stores oxygen in muscles; and mitochondrial enzymes like cytochrome oxidase, which help generate ATP.
Normally, when a red blood cell dies, some iron is recycled from it.
But, we also lose about 1 milligram of iron every day - some through the sweat, some in shedded skin cells, and some in shedded cells in the gastrointestinal tract, which get out of the body through feces.
But most of us take in 10-20 mg of dietary iron every day, and absorb about 10% of it, or about 1 or 2 milligrams - so it all evens out at the end of the day!
Now, our diet contains two forms of iron.
The first is heme iron, or iron bound to hemoglobin or myoglobin, which comes from animal products like meat.
Heme iron is in the ferrous, or Fe2+, state.
The other form is non-heme iron, which is free iron molecules in the ferric, or Fe3+, state.
Non-heme iron comes from plant based foods like spinach and beans.
Now, when food is broken down in the stomach, iron is released.
Heme iron is absorbed directly into the duodenal cells, where it is broken down to release Fe2+ molecules.
Non-heme iron, however, needs to be reduced to heme iron first.
So the stomach’s hydrochloric acid activates a group of enzymes in the duodenal cells, collectively called ferri-reductase, which live up to their name by reducing non-heme iron to Fe2+ molecules.
Fe2+ molecules then bind to a protein in the duodenal cells called ferritin, which temporarily stores the iron.
And when iron is needed in the body, some Fe2+ molecules are released from ferritin and transported into the blood, where the enzyme hephaestin converts them back to the Fe3+ state.
Fe3+ molecules then bind to an iron transport protein called transferrin that carries iron to various target tissues and releases them there.
Fe3+ enters these various tissue cells, where there’s some more ferritin that can store them for future use.
Iron deficiency anemia can develop as a result of four main causes: decreased intake, decreased absorption, increased demand, and increased loss.
Decreased intake is the most common cause of iron deficiency anemia worldwide, and it occurs in infants, because breast milk is surprisingly low in iron; and vegetarians, whose iron intake is mostly nonheme iron, which is harder to absorb.
Decreased absorption can also occur when there’s a decrease in stomach acid production, like after a gastrectomy, where a part of the stomach is surgically removed.
Finally, decreased absorption may occur with inflammatory bowel disease or celiac disease, both of which cause inflammation and destruction of duodenal cells.
Next up, increased demand can occur in children and adolescents due to rapid growth and increase in blood volume, which requires them to make more hemoglobin.
Alternatively, it may occur during pregnancy, due to increased iron requirements for fetal development.
Finally, increased iron loss generally occurs in people with chronic slow bleeding, because iron is lost along red blood cells.
This includes females with frequent or heavy menstruation or people with bleeding gastric ulcers, and, most importantly, elderly males with colon cancer, because the tumor can bleed and cause anemia.
In fact, the first symptom of colon cancer is often iron deficiency anemia.
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- "Iron-Deficiency Anemia" ()
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- "Iron Deficiency Anemia" Medical Clinics of North America (2017)
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- "Iron-Deficiency Anemia" New England Journal of Medicine (2015)
- "Iron deficiency anemia" (2007)