Last reviewed and revised February 27, 2013
Have you ever been told you were anemic? Were you advised to take iron? Did it make you feel better?
Anemia is common. By some estimates, up to 30% of the world's population is anemic. It is particularly common among young women (largely attributed to the blood loss during the menstrual cycle) and in places where nutrition is poor, where chronic disease (such as HIV) is common, or where the water is contaminated with lead or copper.
Because anemia is common, you often hear a recommendation to take iron. But anemia is often blamed for symptoms that are unrelated, and iron deficiency is only one cause of anemia — there are many. Read on for the facts and fiction about anemia.
What Is Anemia?
The word "anemia" means there is a reduction in the number of red blood cells. Even though that may seem like a straightforward definition, it's important next to define "reduction" and there are at least two ways to determine what a "low" number of red cells is:
- Less than the number needed to carry on normal bodily function, or,
- Lower than most other healthy people
It is the latter definition that is usually reported; that is, a laboratory defines its normal values by measuring hundreds or even thousands of normal, healthy people's red blood counts and defining the normal range as the values of 95% of that population. The remaining 5% — the very highest and lowest values — are then considered abnormal.
Red cells are important because they carry oxygen throughout the body. There are several ways to measure and report anemia, the most common of which are volume and concentration of hemoglobin (the oxygen-carrying molecule within the red blood cell).
For adult women, the normal volume of red blood cells, called the hematocrit, ranges from approximately 36% to 48% (representing 95% of the healthy female population as above). The volume is a bit higher for men (40% to 52%). The concentration of hemoglobin is normally 11.5 milligrams per deciliter (mg/dl) to 17.5 mg/dl, with some variation depending on your gender and the laboratory testing the blood.
Keep in mind that if your hematocrit or hemoglobin is slightly low, it could be because you are among the normal people whose values fall below the cut-off of normal. Because 95% of normal people's test results fall within the "normal range" (also called reference range), 5% do not, even though they are also healthy.
It's also important to recognize that even if a blood-test result is normal, if it was previously higher, that could be a sign of trouble; in other words, the result might be normal but because it's lower, the person might be "relatively anemic."
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Anemia — Not a Disease
Anemia is not actually a disease; rather, it is a blood-test result. In normal circumstances, the bone marrow produces more than enough red blood cells to carry oxygen to the vital organs of the body. They last about four months in the circulation and are then broken down and removed from the circulation when they get feeble.
While there are several causes of anemia, the two major categories and some common examples include:
- Problems with red blood cell production, when the bone marrow is producing too few cells; examples include iron, vitamin B12 or folate deficiency (because each of these nutrients is needed to make red cells)
- Problems with red blood cell breakdown, when they are being destroyed faster than they can be made; examples include various forms of hemolytic anemia
Another way to think about the causes of anemia is to divide them into disorders that only affect red cells and conditions in which anemia is only one part of the disease. For instance, in "pure red cell aplasia," the bone marrow simply makes too few red blood cells, but in a person with a bleeding ulcer, iron deficiency anemia is a secondary problem and unlikely to improve without ulcer treatment. Similarly, hemolytic anemia may develop by itself (often called "autoimmune hemolytic anemia" because the body's immune system is thought to mistakenly attack the body's own red cells), or it may be part of a body-wide illness such as lupus.
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Possible Anemia Symptoms
When anemia is "significant," it may be associated with fatigue, headaches, palpitations, shortness of breath and even chest pain leading to heart attack (though usually in persons with underlying heart disease). Symptoms tend to be worst during exertion because exercise requires more oxygen delivery to the muscles. If the anemia is severe and getting worse, symptoms may develop even at rest, and include difficulty breathing, confusion or lethargy. If anemia is due to sudden bleeding, there is not just a reduced number of red cells, there is also a sudden reduction in plasma (the fluid portion of blood), leading to low blood pressure with dizziness or even shock and death.
However, none of these symptoms or conditions is likely to be caused by anemia when the anemia is mild. How to define "significant" or "mild" anemia is somewhat arbitrary, but most experts would agree that hematocrit levels of 32 to 35 are unlikely to cause symptoms; less than 28 may cause symptoms, and in between (28 to 32), symptom development is highly variable — that is, some will and some will not have symptoms related to anemia of this mild to moderate severity.
When a person's anemia is moderate or severe, there may be symptoms not only related to anemia, such as fatigue, but also symptoms related to the disease causing the anemia. For example, anemia is common among people with chronic diseases associated with inflammation, such as rheumatoid arthritis (associated with joint pain and stiffness) or Crohn's disease (associated with diarrhea and crampy abdominal pain).
Finally, when anemia is bad enough to cause symptoms, reducing or eliminating the symptoms is certainly important, but finding the cause is also a priority. In fact, it may be impossible to eliminate symptoms related to anemia without figuring out why anemia developed in the first place.
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When There Are No Symptoms
Most people with mild anemia don't know it because they have no symptoms. Fatigue is often said to result from anemia, yet doctors are taught that unless anemia is "significant," it should not cause symptoms. In fact, fatigue is an extremely common and poorly understood symptom and often can be found in people whose blood counts are completely normal. Even when fatigue is associated with mild anemia, symptoms rarely improve even after the anemia resolves.
There are exceptions, however, to these general rules. For example, even with moderate to severe anemia, symptoms may develop so slowly that they are not appreciated, at least until the anemia is treated. In addition, there is some uncertainty in the area of anemia. A review of anemia in the Archives of Internal Medicine pointed out that people with cancer, heart attack, and those requiring dialysis may feel better if their anemia is treated (for instance, with transfusions) than if their red blood cell counts are allowed to remain low, even when the anemia is mild and there are no clear-cut symptoms related to the anemia.
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The Bottom Line
When anemia is discovered, people often assume that it explains their symptoms, especially fatigue. In many cases, perhaps most, this is a myth, because while anemia may cause fatigue, most fatigue is not caused by anemia. In fact, mild anemia rarely causes fatigue; the proof is that symptoms usually persist even when mild anemia has been corrected.
A search for the cause, including vitamin or nutrient deficiency (such as iron), blood loss, red cell destruction, and underlying inflammation are all important steps. Treatment depends on the severity of the anemia and the underlying cause. To assume that every anemia is due to iron deficiency and that all anemias cause symptoms overlooks the complexity and subtlety of this common condition. A doctor or patient making these assumptions could overlook the true cause of the fatigue.
If you are exceptionally tired, see your health care professional for evaluation, especially if there is no obvious reason (such as lack of sleep). And if you are anemic, it could well be unrelated to your symptoms. Keep an open mind — that way, you are less likely to fall victim to common misconceptions about these common problems.
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Robert H. Shmerling, M.D. is associate physician at Beth Israel Deaconess Medical Center and associate professor at Harvard Medical School. He has been a practicing rheumatologist for over 20 years at Beth Israel Deaconess Medical Center. He is an active teacher in the Internal Medicine Residency Program, serving as the Robinson Firm Chief. He is also a teacher in the Rheumatology Fellowship Program.