Sample Timing, Diagnosis of Subclinical Thyroid Dysfunction and Mortality in Acute Myocardial Infarction: ThyrAMI1
Salman Razvi1,2, Owain Leng3, Avais Jabbar1,3
1Institute of Genetic Medicine, Newcastle University, Newcastle upon Tyne, UK.
Insights
Blood sample timing significantly impacts diagnosing subclinical thyroid dysfunction (SCTD) in acute myocardial infarction (AMI) patients. Accounting for timing is crucial for accurate SCTD diagnosis and assessing mortality risk in AMI.
Area of Science:
- Endocrinology
- Cardiology
- Clinical Diagnostics
Background:
- Subclinical thyroid dysfunction (SCTD) is common in acute myocardial infarction (AMI) patients.
- The timing of blood sample collection may influence thyroid function test results.
Purpose of the Study:
- To investigate the impact of blood sample timing on the diagnosis of SCTD in AMI patients.
- To evaluate the association between sample timing and mortality in AMI patients with SCTD.
Main Methods:
- Prospective evaluation of thyroid function in 1806 AMI patients.
- Analysis of serum thyrotropin (TSH) levels on admission and at least one week later.
- Logistic regression used to assess the association between sample timing and SCTD diagnosis and mortality.
Main Results:
- Prevalence of subclinical hypothyroidism (SCH) was 17.2% and subclinical hyperthyroidism (SHyper) was 1.2%.
- Diagnosis of SCTD varied significantly by blood sample timing (P < .001 for SCH).
- Mortality risk in SCH patients was elevated only when time period-specific TSH ranges were used (HR: 2.26, P = .04).
Conclusions:
- Blood sample timing is a critical factor in diagnosing SCTD in AMI patients.
- Failure to account for sample timing leads to misclassification of SCTD and loss of prognostic information.
- Accurate diagnosis and prognosis of SCTD in AMI require consideration of blood collection time.
Objective:
The objective of this study was to determine the impact of blood sample timing on the diagnosis of subclinical thyroid dysfunction (SCTD) and mortality in patients with acute myocardial infarction (AMI).
Patients, Design, And Main Outcome Measures:
Patients with AMI had thyroid function evaluated on admission between December 2014 and December 2016 and those with abnormal serum thyrotropin (TSH) had repeat thyroid function assessed at least a week later. The association between sample timing and SCTD was evaluated by logistic regression analysis. Secondary outcomes were confirmation of SCTD on repeat testing and all-cause mortality up to June 2018.
Results:
Of the 1806 patients [29.2% women, mean (± standard deviation) age of 64.2 (±12.1) years] analyzed, the prevalence of subclinical hypothyroidism (SCH) was 17.2% (n = 311) and subclinical hyperthyroidism (SHyper) was 1.2% (n = 22) using a uniform TSH reference interval. The risk of being diagnosed with SCTD varied by sample timing in fully-adjusted models. The risk of SCH was highest between 00.01 and 06.00 hours and lowest between 12.01 and 18.00 hours, P for trend <.001, and risk of SHyper was highest between 12.01 hours and 18.00 hours and lowest between 00.01 hours and 06.00 hours. Furthermore, time of the initial sample was associated with the risk of remaining in a SCH state subsequently. Mortality in SCH patients was not elevated when a uniform TSH reference interval was utilized. However, when time period-specific TSH reference ranges were utilized, the mortality risk was significantly higher in SCH patients with HR (95% CI) of 2.26 (1.01-5.19), P = .04.
Conclusions:
Sample timing impacts on the diagnosis and prognosis of SCH in AMI patients. If sample timing is not accounted for, SCH is systemically misclassified, and its measurable influence on mortality is lost.
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