A client with inflammatory bowel disease is taking the immunosuppressant methotrexate. Which laboratory test must be monitored on a regular basis?

Key nursing concept: Monitoring the client receiving methotrexate (MTX)

Methotrexate is an immunosuppressant used not only for inflammatory bowel disease but also for a variety of autoimmune conditions such as rheumatoid arthritis. It is an antimetabolite that inhibits cell division, so it has its strongest effect on rapidly dividing cells. This is how it reduces joint inflammation, but it also suppresses the hematopoietic stem cells of the bone marrow—normal cells that divide rapidly—and can therefore cause myelosuppression.

When myelosuppression occurs, production of all three major blood components—white blood cells, red blood cells, and platelets—declines. A drop in white blood cells (leukopenia) raises the risk of infection; a drop in platelets (thrombocytopenia) raises the risk of bleeding; and a fall in hematocrit (HCT), an index of red blood cells, can produce fatigue and pallor from anemia. In addition, because methotrexate is metabolized by the liver, hepatotoxicity is another major adverse effect. Detecting these toxicities early during therapy is therefore of the highest importance.

Why the complete blood count (CBC)?
The supporting evidence clearly shows that regular monitoring of the complete blood count (CBC) and liver function tests (LFTs) is the standard of care for clients taking methotrexate ^[1]. One study followed clients receiving methotrexate for liver values such as alanine aminotransferase (ALT) and aspartate aminotransferase (AST) along with white blood cell count (WBC), hematocrit (HCT), mean corpuscular volume (MCV), and platelet count (PLT) ^[1]. All of these values are basic parameters included in a CBC and liver function panel.

Another study analyzed changes in hematologic parameters over the first 12 weeks after starting methotrexate and evaluated how those changes correlated with treatment response and disease activity ^[2]. This suggests that beyond simply causing toxicity, changes in blood cell counts themselves can serve as an important predictor of a client's response to the drug. In other words, tracking WBC, platelet, and hemoglobin/hematocrit trends with a CBC provides the evidence base for the nursing interventions needed to detect myelosuppression—a serious adverse effect—early and to adjust the dose or hold the drug when indicated.

Rationale for each option and nursing judgment
* 1. Electroencephalogram (EEG): The main toxicities of methotrexate involve the bone marrow and liver; direct central nervous system toxicity is not a priority monitoring parameter.
* 2. Pulmonary function test (PFT): Methotrexate can rarely cause interstitial pneumonitis, but this test is performed diagnostically when symptoms appear. The top priority for routine follow-up is assessment for myelosuppression and hepatotoxicity.
* 3. Echocardiography: Significant cardiac toxicity has not been reported with methotrexate, so this is not a routine follow-up test.
* 4. Complete blood count (CBC): Correct. It evaluates all blood cell lines produced in the bone marrow and allows early detection of drug-induced myelosuppression. The evidence also identifies WBC, HCT, and PLT as key monitoring parameters ^[1][2].
* 5. Arterial blood gas analysis (ABG): This test evaluates pulmonary gas exchange and acid–base balance and is not related to routine monitoring of methotrexate adverse effects.

Therefore, when caring for a client on methotrexate, the nurse should keep the scheduled blood draws and closely assess whether WBC, platelet, and hemoglobin values fall below normal limits (myelosuppression) and whether AST/ALT are rising (hepatotoxicity). If the WBC falls below 3,000/mm³ or the platelet count falls below 100,000/mm³, the risk of infection and bleeding rises sharply, so the nurse must notify the provider immediately and verify whether the drug should be held.