Anemia - Diagnosis

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Diagnosing Megaloblastic Anemia. Very large oval red blood cells indicate megaloblastic anemia. Abnormally shaped neutrophils (certain white blood cells) may also be present. Bone marrow aspiration may need to be performed if the disease is strongly suspected but the diagnosis is not clear.

Determining Vitamin Deficiency. Once megaloblastic anemia has been diagnosed, the doctor will need to determine which vitamin deficiency is causing it. This is extremely important, because if a vitamin B12-deficient patient receives folate replacement only, then irreversible nerve injuries may develop. Even if blood tests for megaloblastic anemia are normal, patients with neurologic and psychiatric abnormalities that have no detectable cause should still be tested for vitamin B12 deficiency.

Deficiencies may be suggested by the presence of other disorders:

• Malnutrition, alcohol abuse, pregnancy, a history of sprue, severe psoriasis, or the use of antiseizure drugs may indicate a folic acid deficiency.
• A history of stomach surgery, eating raw fish (which raises the possibility of tapeworm), inflammatory bowel disease, or hypothyroidism suggests vitamin B12 deficiency.

Often, vitamin B deficiencies cannot be determined by a history or symptoms alone. Blood tests are the primary indicators of both vitamin B12 and folic acid deficiencies, but even blood tests for these vitamins are not always straightforward:

• Folic acid and vitamin B12 levels must always be measured at the same time because each vitamin may affect the other.
• Folate levels may be temporarily low in some people who are not truly deficient.
• Folate levels may temporarily rise in deficient people if they have just eaten foods containing the vitamin.
• Antibiotics can interfere with B12 levels.

Measuring methylmalonic acid and homocysteine, substances in the blood that increase when levels of one or both vitamins are low, improves accuracy.

Tests for Pernicious Anemia. Once a vitamin B12 deficiency has been established and the doctor has not found any intestinal abnormalities or other factors to account for the deficiency, the doctor presumes a diagnosis of pernicious anemia. Pernicious anemia may also be diagnosed through various blood (such as complete blood count) or urine tests.

Pernicious anemia is treated with vitamin replacement, but the condition is easily missed, particularly in patients whose diets are rich in folic acid. Folic acid can mask the early symptoms of pernicious anemia but not cure it. Consequently the disease may persist until serious neurologic symptoms occur. With folic acid now a required additive in many commercial foods, some experts are concerned about an increased incidence in pernicious anemia.

Review Date: 01/17/2007
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital