From the Guidelines
A complete blood count (CBC) should be checked in a patient with depression to rule out underlying medical conditions that can cause or exacerbate depressive symptoms. This is crucial because certain medical conditions, such as anemia, thyroid dysfunction, or infections, can present with symptoms that mimic or worsen depression, and a CBC can help identify these conditions. For instance, anemia, particularly iron, B12, or folate deficiency, can cause fatigue, weakness, and cognitive changes that may be mistaken for depressive symptoms 1. Furthermore, a CBC can provide valuable baseline information before starting certain antidepressants that may affect blood counts, and abnormal results might prompt further testing to rule out underlying medical causes of depression. Some key points to consider when checking a CBC in a patient with depression include:
- Ruling out anemia, which can be suggested by abnormal red blood cell indices, and may manifest as fatigue, weakness, and cognitive changes
- Detecting signs of infection or inflammation that might contribute to mood disturbances
- Providing baseline information before starting certain antidepressants that may affect blood counts
- Prompting further testing, such as iron studies, vitamin B12 levels, or thyroid function tests, if abnormal CBC results are found. It is essential to note that while the US Preventive Services Task Force recommendation statement on screening for depression in adults does not specifically mention the use of CBC in diagnosing depression, it highlights the importance of considering medical conditions that may contribute to depressive symptoms 1. Therefore, checking a CBC in a patient with depression is a reasonable approach to ensure that underlying medical conditions are not missed and to establish a safe foundation for psychiatric treatment.
From the Research
Rationale for Checking CBC in Patients with Depression
- A complete blood count (CBC) can be useful in assessing patients with depression, particularly in relation to inflammatory markers and potential cardiovascular or metabolic comorbidities 2, 3.
- Studies have shown that changes in CBC parameters, such as elevated neutrophil-to-lymphocyte ratio (NLR), platelet-to-lymphocyte ratio (PLR), and monocyte-to-lymphocyte ratio (MLR), may be associated with depression and suicidality severity 2.
- Additionally, patients with depression may be at risk for cardiovascular and metabolic diseases, which can be predicted using CBC components, including white blood cell count, NLR, hemoglobin, and platelet count 3.
Relationship Between CBC and Depression
- Research has found that patients with major depressive disorder (MDD) may have higher WBC counts, neutrophil percentages, and platelet counts, as well as lower lymphocyte percentages, compared to healthy controls 2.
- The NLR, PLR, and MLR have been identified as potential biomarkers for depression and suicidality risk, with higher ratios associated with increased severity of symptoms 2.
Considerations for Patients with Depression
- When treating patients with depression, particularly those with suicidal ideation or attempts, it is essential to consider the potential relationship between CBC parameters and disease severity 2.
- While selective serotonin reuptake inhibitors (SSRIs) are commonly used to treat depression, they may have effects on thyroid function, which can be monitored using CBC parameters 4, 5.
- However, the clinical significance of these effects is unclear, and more research is needed to fully understand the relationship between SSRIs, thyroid function, and depression 4, 5.