Restless Legs Syndrome and Related Disorders - Diagnosis

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Diagnosing Iron Deficiency Anemia and Its Causes

Because of the high association between restless legs syndrome and iron deficiency, a test for low iron stores should be part of the diagnostic workup in RLS. There are two steps in making this diagnosis:

• The first step is to determine if a person is actually deficient in iron.
• If iron stores are low, the second step is to diagnose the cause of the iron deficiency, which will help determine treatment.

Determining if Iron Stores are Low: The following findings are important in determining that a person is iron deficient:

• Blood cells viewed under the microscope are pale (hypochromic) and abnormally small (microcytic). These findings suggest iron deficiency, but they can also appear in anemia resulting from chronic disease, and in thalassemia (an inherited blood disorder).
• Hemoglobin and iron levels are low. These findings further suggest iron deficiency, but they can also occur in cases of anemia due to chronic disease.
• Ferritin levels are low. Ferritin is a protein that binds to iron, and low levels typically mean patients do not have enough iron in their bodies. However, normal levels of ferritin in the blood do not always mean a patient has enough iron. For example, pregnant women in their third trimester or patients with a chronic disease may not have enough iron even with normal or high ferritin levels.
• A test that measures a factor called serum transferrin receptor (TfR) is proving to be very sensitive in identifying iron deficiency in some patients, including the elderly with chronic diseases and possibly pregnant women.

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When iron deficiency anemia is diagnosed, the next step is to determine what causes the iron deficiency itself. Menstrual blood loss is a common cause of iron deficiency. Tests to check for an underlying cause of iron deficiency, such as gastrointestinal (digestive tract) bleeding, are particularly important in men, postmenopausal women, and children. [See In-Depth Report #57: Anemia.]

Other Laboratory Tests

Certain laboratory tests may be helpful in determining causes of restless legs syndrome (RLS) or conditions that rule it out. They include:

• Blood glucose tests for diabetes
• Tests for kidney problems
• In certain cases, tests for thyroid hormone, magnesium, and folate levels
• Electromyography (recording the electrical activity of muscles) for neuropathy, radiculopathy (problem with the nerve roots), myelopathy (problem with the spinal cord)
• Central nervous system MRI for myelopathy or stroke