Content continues after advertisement

Differential Diagnosis: Increased or Decreased Total Thyroxine

Shanna Hillsman, LVMT, University of Tennessee

M. Katherine Tolbert, DVM, PhD, DACVIM (SAIM), Texas A&M University

Endocrinology & Metabolic Diseases

|September 2018|Peer Reviewed|Web-Exclusive

Sign in to Print/View PDF

Following are differential diagnoses, listed in order of likeliness, for patients presented with increased or decreased total thyroxine (T4).

Increased Total Thyroxine

  • Hyperthyroidism
    • Functional benign adenomatous hyperplasia
    • Functional thyroid carcinoma
    • Thyroxine oversupplementation
    • Dietary causes
  • Analytical error (eg, false positive)

Decreased Total Thyroxine

  • Nonthyroidal illness (eg, euthyroid sick syndrome)
  • Hypothyroidism
    • Lymphocytic thyroiditis
    • Thyroid atrophy
    • Iatrogenic secondary to radioactive iodine therapy
    • Methimazole therapy
    • Thyroid neoplasia
    • Sulfonamides
    • Congenital
  • Hyperadrenocorticism
  • Drug effects
    • Phenobarbital
    • Potassium bromide
    • Carprofen
    • Clomipramine
    • Glucocorticoids
    • Propranolol
  • Analytical error


For global readers, a calculator to convert laboratory values, dosages, and other measurements to SI units can be found here.

All Clinician's Brief content is reviewed for accuracy at the time of publication. Previously published content may not reflect recent developments in research and practice.

Material from Clinician's Brief may not be reproduced, distributed, or used in whole or in part without prior permission of Educational Concepts, LLC. For questions or inquiries please contact us.


Clinician's Brief:
The Podcast
Listen as host Alyssa Watson, DVM, talks with the authors of your favorite Clinician’s Brief articles. Dig deeper and explore the conversations behind the content here.
Clinician's Brief provides relevant diagnostic and treatment information for small animal practitioners. It has been ranked the #1 most essential publication by small animal veterinarians for 9 years.*

*2007-2017 PERQ and Essential Media Studies

© 2023 Educational Concepts, L.L.C. dba Brief Media ™ All Rights Reserved. Terms & Conditions | DMCA Copyright | Privacy Policy | Acceptable Use Policy