Which laboratory test is essential for diagnosing atrial fibrillation in an elderly patient?

Thyroid-stimulating hormone (TSH) testing is critical for diagnosing atrial fibrillation, particularly in elderly patients. Atrial fibrillation can often be associated with hyperthyroidism, a condition where the thyroid gland overproduces thyroid hormones, leading to an increase in heart rate and a higher risk of developing arrhythmias, including atrial fibrillation.

Elevated levels of thyroid hormones can cause the heart to become more irritable and lead to the development of this arrhythmia, especially in older adults who may have underlying thyroid dysfunction. Testing TSH levels helps determine if a thyroid disorder is present that could be contributing to the onset of atrial fibrillation.

In contrast, the other laboratory tests listed do not directly address the potential causes or indicators of atrial fibrillation. A complete blood count could provide information about overall health or anemia, but it does not assess cardiac arrhythmias. C-reactive protein is a marker for inflammation and, while it may indicate underlying inflammatory or cardiovascular issues, it is not specific for diagnosing atrial fibrillation. A comprehensive metabolic panel can evaluate electrolyte levels and kidney function but lacks specificity in relation to atrial fibrillation diagnosis.

Thus, testing for thyroid-stimulating hormone is essential in