LabMed

Drug-Induced Neutropenia

At a Glance

Drug-induced neutropenia is characterized by a decline in absolute neutrophil counts precipitated by exposure to a medication. Neutropenia can occur at any time during the course of treatment but most commonly occurs within the first few weeks after initiation of drug therapy. The clinical consequence of neutropenia is susceptibility to infection proportional to the degree of neutropenia. Although patients with drug-induced neutropenia could present with any infectious disease, the most common presenting symptoms are fever, myalgia, and sore throat.

What Tests Should I Request to Confirm My Clinical Dx? In addition, what follow-up tests might be useful?

Neutropenia is diagnosed by complete blood count (CBC) with differential to determine the absolute neutrophil count (ANC). Hemoglobin/hematocrit and platelet count should be normal.

Bone marrow biopsy may be considered. It will show decreased granulopoiesis with intact erythroid and megakaryocyte production. However, this pattern is not necessarily specific to drug-induced neutropenia, as it can be seen in other causes of neutropenia as well.(Table 1)

Table 1.

Test Results Indicative of the Disorder
Absolute Neutrophil Count
1000-1500/μL [mild]
ANC 500-1000/μL [moderate]
<500/μL [severe]

Are There Any Factors That Might Affect the Lab Results? In particular, does your patient take any medications - OTC drugs or Herbals - that might affect the lab results?

There are many medications that can result in drug-induced neutropenia. The most common are carbimazole, clozapine, dapsone, dipyrone, methimazole, penicillin G, procainamide, propylthiouracil, rituximab, sulfasalazine, and ticlopidine. Other commonly used drugs that cause neutropenia at lower rates include angiotensin converting enzyme (ACE) inhibitors, H2 blockers, non-steroidal anti-inflammatory drugs (NSAIDs), and antiarrhythmic drugs, among others. A complete list of drug-related agranulocytosis case reports can be found at www.adverse-effects.com/documents/case_reports_agranulocytosis.pdf.

Neutropenia is a nonspecific finding, so other causes should be considered, including autoimmune diseases, nutritional deficiencies, infectious diseases, and congenital disorders.

What Lab Results Are Absolutely Confirmatory?

Confirmation of drug-induced neutropenia is made by repeating the CBC and differential after withdrawal of the offending drug. The neutropenia usually resolves within 3 weeks.

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