doctor confused by thyroid blood work

Normal Lab Testing

Thyroid Function Tests (TFTs) are among the most commonly requested lab investigations. For most of the population, interpreting the lab work is fairly straightforward when we look at a combination of TSH, T4 and perhaps T3. Learn more about the routine lab work here.

For a quick review of Basic Thyroid Anatomy and Physiology, please click here.

a full schematic of thyroid physiology, including hypothalamus, anterior pituitary gland, thyroid gland and the hormones TSH, T3 and T4

As doctors, we learn to diagnose thyroid disease through a combination of clinical findings (signs/symptoms) as well as blood tests. Sometimes, the blood work doesn’t make sense. We expect the following:

a schematic showing thyroid metabolism in hypothyroidism, including T3 and T4 and how when they drop, TSH will increase
thyroid physiology involved in hyperthyroidism showing T3 and T4 hormones have increased expression while TSH drops

Confusing Lab Results

Results of thyroid function tests can seem confusing, either because they conflict with the clinical symptoms or because they appear in an unusual pattern with each other [1].

As a Naturopath, a high proportion of my patients fall out of the normal paradigm of thyroid testing; they often have ‘confusing’ results. This article focuses on the common causes of these results.  Establishing a correct diagnosis is very important, and depends on careful clinical assessment, combined with further lab, radiological and genetic testing [2].

How Do Anomalous Thyroid Function Tests Arise?

There are a number of scenarios, each of which we will address below, but they generally fall under one of three categories [1]:

  1. Altered ‘normal physiology’
  2. Genetic defects
  3. Interference in one or more lab assays

Patients and doctors alike must recognize the sources of these anomalous tests and see the pitfalls of relying purely on blood work when making diagnoses or treatment plans. A structured approach to further investigate abnormal lab tests is required to ensure resources are not wasted and make appropriate treatment recommendations.

How Do These “Confusing” Lab Results Present?

Legend:         ↔: normal     ↑increased          ↓decreased

First let’s recap a normal, expected result (this is how most patients will present):


  • This is a healthy, normal thyroid


  • Possible causes: autoimmune thyroiditis (Hashimoto’s, atrophic), post-radioiodine therapy/thyroidectomy, hypothyroid phase of thyroiditis, drugs (amiodarone, lithium, TKI’s, ATD’s), iodine deficiency or excess, neck irradiation, Riedel’s thyroiditis, thyroid infiltration (tumor, amyloid), congenital hypothyroidism [1]


  • Possible causes: Graves' disease, toxic multinodular goiter, toxic adenoma, thyroiditis (post viral, post-partum), drugs (amiodarone), excess Iodine intake, excess thyroxine ingestion, pregnancy-related (hyperemesis gravidarum; hydatidiform mole), congenital hyperthyroidism [1]

The ‘confusing’ results can present in a number of ways.

The causes are listed here, and a brief summary provided further below. More in depth articles may be reached by clicking the links provided.

↓TSH, ↔FT4/FT3

  • Subclinical hyperthyroidism, recent treatment for hyperthyroidism, drugs (pharmaceutical and recreational), NTI (non-thyroidal injury), assay interference [1],[2]

↑TSH, ↔FT4/FT3

  • Subclinical hypothyroidism, poor compliance with thyroxine, malabsorption of thyroxine, drugs, assay interference, NTI (non-thyroidal injury) recovery phase, TSH resistance [1], [2]

↔ or ↓TSH, ↓FT4/FT3

  • NTI (non-thyroidal injury), central hypothyroidism, isolated TSH deficiency, assay interference [1], [2]

↔ or ↑TSH, ↑FT4/FT3

  • Assay interference: FDH (familial dysalbuminemic hyperthyroxinaemia), thyroxine replacement therapy (including poor performance), drugs (amiodarone, heparin), NTI (including psychiatric disorders), neonatal period, TSH-secreting pituitary adenoma, resistance to thyroid hormone, disorders of thyroid hormone transport or metabolism [1], [2]

Common Causes of Confusing Thyroid Lab Work

There are various cases of the above alterations to thyroid blood work. If you every have abnormal thyroid results that DO NOT fall into the usual categories, make sure your doctor is investigating these possible contributing factors.

  1. Drug/Medication Interactions with Thyroid function
  2. Poor Compliance of Thyroxine Therapy
  3. Altered Thyroid Binding Proteins
  4. Non-Thyroidal Illness or Sick Euthyroid Syndrome
  5. Assay Interference
  6. Resistance to TSH or TSHoma


As you can see, there are various reasons thyroid blood test results may come back and not look as expected. They seem confusing, but with deeper analysis, we can investigate any of the above causes of anomalous thyroid rest results.


Interested in learning more?

Read on in our series of articles on Thyroid Health!

About the Author - Dr. Johann de Chickera

man facing camera

Dr. Johann is a fully licensed Naturopathic Doctor. His approach emphasizes the importance of living a healthy lifestyle and improving one’s health naturally. Dr. Johann obtained a Doctor of Naturopathy at the Canadian College of Naturopathic Medicine (CCNM). Education at CCNM is a vigorous four years, with a curriculum involving biomedical sciences, physical diagnosis, clinical nutrition, traditional Chinese medicine and acupuncture, botanical (herbal) medicine, physical medicine, homeopathy and lifestyle management.

While Dr. Johann has a general practice, he focuses on fertility, hormonal imbalances, gut health, and autoimmune disease.

To book in please call us at (519) 442-2206 or click here.

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