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Validation of a decision rule for selective TSH screening in atrial fibrillation
Shawna D Bellew1, Rajat Moman2, Christine M Lohse3
1Mayo Clinic, Department of Emergency Medicine, Rochester, Minnesota.
Insights
Thyroid-stimulating hormone (TSH) testing in emergency department patients with atrial fibrillation (AF) is rarely low. A clinical decision rule for ordering TSH tests in AF patients showed limited accuracy, suggesting selective testing is more appropriate.
Area of Science:
- Cardiology
- Endocrinology
- Emergency Medicine
Background:
- Atrial fibrillation (AF) is a common cardiac arrhythmia.
- Current guidelines suggest thyroid-stimulating hormone (TSH) testing for all AF patients.
- The utility of TSH testing in the emergency department (ED) for AF requires further investigation.
Purpose of the Study:
- To evaluate the diagnostic utility of TSH levels in ED patients diagnosed with AF.
- To externally validate and refine a clinical decision rule for TSH testing in AF patients.
- To assess the prevalence of abnormal TSH levels in this patient population.
Main Methods:
- Retrospective, cross-sectional study of consecutive ED patients with AF.
- Chart review for patient history (stroke, hypertension, thyroid disease) and TSH levels.
- Assessment of the sensitivity and specificity of a clinical decision rule for identifying abnormal TSH.
Main Results:
- Low TSH (<0.3μIU/mL) was found in 2% of 1,458 analyzed patients.
- Elevated TSH (>5μIU/mL) was identified in 11% of patients.
- The clinical decision rule showed 88.9% sensitivity and 27.5% specificity for low TSH; 74.4% sensitivity and 27.3% specificity for any abnormal TSH.
Conclusions:
- Abnormal TSH levels are uncommon in ED patients with AF.
- The existing clinical decision rule for TSH testing in AF patients has suboptimal sensitivity and specificity.
- Routine TSH testing in all AF patients presenting to the ED is not recommended; selective testing in new-onset AF or those with thyroid history is suggested.
Introduction:
Atrial fibrillation (AF) is the most common cardiac dysrhythmia. Current guidelines recommend obtaining thyroid-stimulating hormone (TSH) levels in all patients presenting with AF. Our aim was to investigate the utility of TSH levels for emergency department (ED) patients with a final diagnosis of AF while externally validating and potentially refining a clinical decision rule that recommends obtaining TSH levels only in patients with previous stroke, hypertension, or thyroid disease.
Methods:
We conducted a retrospective, cross-sectional study of consecutive patients who presented to an ED from January 2011 to March 2014 with a final ED diagnosis of AF. Charts were reviewed for historical features and TSH level. We assessed the sensitivity and specificity of the previously derived clinical decision rule.
Results:
Of the 1,964 patients who were eligible, 1,458 (74%) had a TSH level available for analysis. The overall prevalence of a low TSH (<0.3μIU/mL) was 2% (n=36). Elevated TSH levels (>5μIU/mL) were identified in 11% (n=159). The clinical decision rule had a sensitivity of 88.9% (95% CI [73.0-96.4]) and a specificity of 27.5% (95% CI [25.2-29.9]) for identifying a low TSH. When analyzed for its ability to identify any abnormal TSH values (high or low TSH), the sensitivity and specificity were 74.4% (95% CI [67.5-80.2]) and 27.3% (95% CI [24.9-29.9]), respectively.
Conclusion:
Low TSH in patients presenting to the ED with a final diagnosis of AF is rare (2%). The sensitivity of a clinical decision rule including a history of thyroid disease, hypertension, or stroke for identifying low TSH levels in patients presenting to the ED with a final diagnosis of atrial fibrillation was lower than originally reported (88.9% vs. 93%). When elevated TSH levels were included as an outcome, the sensitivity was reduced to 74.4%. We recommend that emergency medicine providers not routinely order TSH levels for all patients with a primary diagnosis of AF. Instead, these investigations can be limited to patients with new onset AF or those with a history of thyroid disease with no known TSH level within three months.
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