Merck Manual

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Diagnosing Underlying Disorders in Patients With Anemia—Commentary

02/28/18 Evan M. Braunstein, MD, PhD, Johns Hopkins University School of Medicine;

Anemia is one of the more common reasons patients are referred to a hematologist. And although most primary practitioners start the anemia workup appropriately, it’s worth going over a few points about the disorder. Important things to remember include:

  • Anemia is not a diagnosis, but rather an indicator of an underlying disorder.
  • The severity of the anemia doesn’t always match the significance of its cause.
  • Although advanced lab testing is often needed, a thorough history and physical and a peripheral smear can often suggest the diagnosis or at least guide subsequent testing.

Anemia is not a diagnosis

If a patient’s Hb is low (< 14 g/dL for men and < 12 g/dL for women), there must be a reason. Of course, the reasons are numerous and range from relatively benign nutritional disorders to life-threatening malignancies and bone marrow problems. That makes determining the etiology of anemia essential.  

The severity of anemia doesn’t always match the significance of its cause

Anemia usually comes on slowly, often over weeks to months. That means that even anemias caused by serious problems (eg, malignancy), may show up at an early stage, when the anemia is quite mild. Conversely, anemia due to relatively benign causes (eg, heavy menses) can become highly symptomatic if not diagnosed and treated for a prolonged time.

A thorough history and physical plus a peripheral smear should guide the workup

Before ordering a battery of tests on anemic patients, review their H&P for symptoms and signs of

  • Blood loss
  • Malabsorption
  • Nutritional deficiencies
  • Occult malignancy
  • Chronic inflammatory conditions (eg, infection, autoimmune disorders, kidney disease)
  • Hemolysis

When disorders in these categories are severe or chronic enough to cause anemia, they typically also leave clues in the H&P. Some of the manifestations, of course, are part of standard office review of systems. But some details will likely require additional focused questioning and examination.

A brief editorial cannot delve into all the relevant components of H&P, but one element worth mentioning is pica (the urge to chew ice, dirt or other non-food material). Pica is a common symptom of iron deficiency that patients rarely volunteer without being specifically asked.  

Iron deficiency has also been linked to restless leg syndrome (RLS). Everyone with RLS should be tested for iron deficiency and treated if iron stores are low.

Also make sure the evaluation identifies manifestations of disorders that may be worsened by anemia, particularly disorders with inadequate tissue perfusion (eg, coronary or cerebral vascular disease, heart failure) or inadequate oxygenation (eg, COPD). Such patients do not tolerate anemia as well as others.

A peripheral blood smear (assessed by an appropriate expert) is a valuable tool that’s often underutilized and should be done along with the detailed H&P. The smear is a vital test that’s simple, inexpensive and can significantly narrow the differential diagnosis (and thus subsequent testing).

Avoid presumptions

Physicians must at least consider less common causes of anemia, even when a patient matches a common demographic for a particular type of anemia. For example, iron deficiency anemia in a 40-year-old woman is likely caused by heavy periods, but could also be an indicator of celiac disease or a colon malignancy.

It’s also crucial to note that anemia is not a normal consequence of aging. Anemia of the elderly has been debunked. While older patients are more likely to experience symptoms with mild anemia, any anemia should be investigated and the etiology identified.

Discussing anemia with patients

Patients must understand that their anemia always has a cause. Identifying and treating that underlying condition is the key to eliminating the anemia. When patients realize this, they’re better able to monitor and describe their symptoms, follow a treatment plan and work to improve their overall health.

For additional information and education, physicians can refer patients to the discussion of anemia in the consumer version of the Manual.