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Cited by 6Thyroid Disorders and TreatmentsThyroid and Parathyroid SurgeryThyroid Cancer Diagnosis and Treatment

Validity of the Rapid Thyroxine Absorption Test for the Differentiation Between Levothyroxine Non-compliance and Malabsorption in Thyroid-Stimulating Hormone Refractory Hypothyroidism

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Alhassan, Akram A, Alidrisi, Haider A, Mansour, Abbas A·2023·Cureus
DOI 10.7759/cureus.37776PMC PMC10194831
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Abstract

Introduction Thyroid-stimulating hormone refractory hypothyroidism is a common problem. This is due to either non-compliance or malabsorption with levothyroxine (LT4). The study aimed to assess the validity of the rapid LT4 absorption test in the differentiation between LT4 malabsorption and non-compliance. Methods A cross-sectional study was done from January to October 2022 at Faiha Specialized Diabetes, Endocrine, and Metabolism Center, in Basrah, Southern Iraq. Twenty-two patients with thyroid-stimulating hormone (TSH) refractory hypothyroidism were evaluated by rapid LT4 absorption test with measurements of TSH before 1000 μg LT4 intake, and free thyroxine (pmol/l) and total thyroxine before (nmol/l) (baseline TT4 and baseline FT4) and two hours after (2-HR TT4 and 2-HR FT4). The findings were compared with the following four-week-long supervised LT4 absorption test results. Results In the rapid LT4 absorption test, patients with (2-HR FT4 minus baseline FT4 ≤1.28 pmol/l (0.1 ng/dl) or 2-HR FT4 minus baseline FT4 1.28-6.43 pmol/l (0.1-0.5 ng/dl) plus 2-HR TT4 minus baseline TT4<72.08 nmol/l (5.6 µg/dl)), eight out of 10 patients were correctly diagnosed with malabsorption. And in those with (2-HR FT4 minus baseline FT4 ≥6.43 (0.5 ng/dl) or 2-HR FT4 minus baseline FT4 1.28-6.43 (0.1-0.5 ng/dl) plus 2-HR TT4 minus baseline TT4≥72.08 (5.6 µg/dl)), 11 out of 12 patients were correctly diagnosed as non-compliant. This criterion showed 88.8% sensitivity, 15.4% specificity, 80% positive predictive value, and 91.6% negative predictive value for diagnosing LT4 malabsorption. Conclusion The rapid LT4 absorption test showed good diagnostic accuracy in differentiating non-compliance from malabsorption when (2-HR FT4 minus baseline FT4) and (2-HR TT4 minus baseline TT4) were used as criteria.

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  • The levothyroxine absorption test is not standardized, and multiple protocols have been published with differences regarding test dose, formulations, test durations, frequency of blood collections, analyte, metric, and thresholds for normal absorption.

    “So far, the levothyroxine absorption test is not standardized [7-18], and multiple protocols have been published with differences regarding the test dose, formulations, test durations, frequency of blood collections, analyte (total T4, free T4), metric (absolute or relative peak or increment), and thresholds for normal absorption.”

    From Levothyroxine Absorption Test With the Daily Levothyroxine Dose in Patients With “Refractory Hypothyroidism” (2025) · cites this paper as [7]

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Research works printed but not linked: 2

  1. [18][Pseudomalabsorption of levothyroxine: a case report] Arq Bras Endocrinol Metabol Pedrosa W Santana G 308 313 49 2005 16184262
  2. [20]Rapid levothyroxine (Lt4) absorption test for diagnosis of lT4 pseudomalabsorption: case report and proposal of a cutoff point J Endocrinol Diabetes Obes Soares R de Figueiredo R Melo Dantas M 1083 4 2016 https://www.jscimedcentral.com/jounal-article-pdfd/Journal-of-Endocrinology%2C-Diabetes-and-Obesity/endocrinology-4-1083.pdf

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Authors
Alhassan, A. A., Alidrisi, H. A., & Mansour, A. A.
Affiliations
University of Basrah (IQ)
Corresponding author
Alidrisi, Haider A
ORCID
Venue
Cureus
Publisher
Springer Science and Business Media LLC
Published
2023-04-18
Volume
15
Issue
4
Pages
e37776-e37776
ISSN
2168-8184 (ISSN-L)
DOI
10.7759/cureus.37776
PMC
PMC10194831
OpenAlex
W4366262854
Cited by
6
References
26
Citations by year
2026: 3 · 2025: 1 · 2024: 1 · 2023: 1
FWCI
1.23
Type
journal article
Language
en
Open access
Licence
cc-by
Locations
  • Cureus (publishedVersion, cc-by)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
Topics
  • Health Sciences › Medicine › Endocrinology, Diabetes and Metabolism › Thyroid Disorders and Treatments
  • Health Sciences › Medicine › Surgery › Thyroid and Parathyroid Surgery
  • Health Sciences › Medicine › Endocrinology, Diabetes and Metabolism › Thyroid Cancer Diagnosis and Treatment
Keywords
free thyroxine, total thyroxine, diagnostic accuracy, thyroid hormone replacement, sensitivity and specificity, positive and negative predictive value

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