Test description: Serum total triiodothyronine (T3T) measurement.
Comments: Although T3T is a biologically active thyroid hormone, it has limited use in the diagnosis of hypothyroidismdue to the high prevalence of autoantibodies (T3AA), which can cause false results.

• Sample type: Serum
• Species: Canine, Feline, Equine
• Recommended volume: 0.7 mL
• Minimum volume: 0.5 mL
• Container: Tube with a red or yellow cap, without a gel separator
• Fasting: 8 a.m. to 12 p.m.
• Rejection Criteria: Hemolyzed, lipemic, or insufficient sample volume

• Reduced levels may occur in hypothyroidism, but they are not very specific.

• It should always be interpreted in conjunction with T4, TSH, and a clinical evaluation.

Test Method
Radioimmunoassay (RIA) or Chemiluminescent Immunoassay (CLIA).

Test description: Serum total thyroxine (T4T) assay.
Comments: Test primarily indicated for monitoring levothyroxine replacement therapy. On its own, it has limited sensitivity and specificity for diagnosing hypothyroidism, as it is influenced by various non-thyroidal conditions and medications.

• Sample type: Serum
• Species: Canine, Feline, Equine
• Recommended volume: 0.7 mL
• Minimum volume: 0.5 mL
• Container: Tube with a red or yellow cap, without a gel separator
• Fasting: 8 a.m. to 12 p.m.
• Rejection Criteria: Hemolyzed sample, lipemic sample, sample containing a separating gel, or sample with insufficient volume

• Low values: may occur in up to 25% of clinically euthyroid dogs (sick euthyroid syndrome).

• High values: usually related to levothyroxine supplementation.

• It is affected by glucocorticoids, phenobarbital, bromide, and sulfonamides.

Test Method
Radioimmunoassay (RIA)

Test description: Serum total thyroxine (T4T) assay.
Comments: Test primarily indicated for monitoring levothyroxine replacement therapy. On its own, it has limited sensitivity and specificity for diagnosing hypothyroidism, as it is influenced by various non-thyroidal conditions and medications.

• Sample type: Serum
• Species: Canine, Feline, Equine
• Recommended volume: 0.7 mL
• Minimum volume: 0.5 mL
• Container: Tube with a red or yellow cap, without a gel separator
• Fasting: 8 a.m. to 12 p.m.
• Rejection Criteria: Hemolyzed sample, lipemic sample, sample containing a separating gel, or sample with insufficient volume

• Low values: may occur in up to 25% of clinically euthyroid dogs (sick euthyroid syndrome).

• High values: usually related to levothyroxine supplementation.

• It is affected by glucocorticoids, phenobarbital, bromide, and sulfonamides.

Test Method
Chemiluminescence (CLIA)

Test description: Serum free thyroxine (FT4) measurement by equilibrium dialysis, considered the gold standard for assessing the free fraction of the hormone.
Comments: A technique that eliminates interference from binding proteins and autoantibodies (e.g., TgAA), providing more specific and reliable results. Recommended in cases with inconclusive total T4 results or when interfering medications are being used.

• Sample type: Serum
• Species: Canine, Feline
• Recommended volume: 1 mL
• Minimum volume: 0.6 mL
• Container: Tube with a red or yellow cap, without a gel separator
• Fasting: 8 a.m. to 12 p.m.
• Rejection Criteria: Hemolyzed sample, lipemic sample, sample containing a separating gel, or sample with insufficient volume

• Low values: strongly suggestive of true hypothyroidism, and less susceptible to the influence of non-thyroidal illnesses.

• Normal values: help rule out hypothyroidism in patients with low T4 levels due to a concomitant condition.

Test Method
Radioimmunoassay (RIA) after equilibrium dialysis.

Test description: Serum free thyroxine (FT4) assay performed by immunoassay on the Immulite 2000 platform (CLIA).
Comments: A practical technique, validated for dogs, cats, and horses. Although it is influenced by binding proteins and autoantibodies, it is useful as a routine test due to its speed and accessibility, and is especially recommended for therapeutic monitoring.

• Sample type: Serum
• Species: Canine, Feline, Equine
• Recommended volume: 0.7 mL
• Minimum volume: 0.5 mL
• Container: Tube with a red or yellow cap, without a gel separator
• Fasting: 8 a.m. to 12 p.m.
• Rejection Criteria: Hemolyzed sample, lipemic sample, sample containing a separating gel, or sample with insufficient volume

• Low values: may indicate hypothyroidism, but are more susceptible to interference from concomitant diseases and antibodies compared to T4LDE.

• Normal values: suggest that thyroid function is normal.

• It is recommended that results be interpreted in conjunction with free TSH and clinical evaluation.

Test Method
Chemiluminescence (CLIA – Immulite 2000).

Test description: Serum canine thyroid-stimulating hormone (cTSH) assay.
Comments: A pituitary hormone that regulates thyroid function, used in conjunction with T4 (total or free) to diagnose hypothyroidism.

• Sample type: Serum
• Species: Canine
• Recommended volume: 0.7 mL
• Minimum volume: 0.5 mL
• Container: Tube with a red or yellow cap, without a gel separator
• Fasting: 8 a.m. to 12 p.m.
• Rejection Criteria: Hemolyzed sample, lipemic sample, sample containing a separating gel, or sample with insufficient volume

• High values: expected in 80–85% of hypothyroid dogs; high specificity.

• Normal values: do not rule out hypothyroidism (limited sensitivity).

• It should always be interpreted in conjunction with T4 (total or free) and the patient’s medical history.

Test Method
Chemiluminescent Immunoassay (CLIA).

Test description: Detection of serum antibodies against thyroglobulin (TGAA).
Comments: Immunological marker of chronic lymphocytic thyroiditis, the leading cause of primary hypothyroidism in dogs. It can identify predisposed animals before obvious hormonal changes occur.

• Sample type: Serum
• Species: Canine
• Recommended volume: 0.7 mL
• Minimum volume: 0.5 mL
• Container: Tube with a red or yellow cap, without a gel separator
• Fasting: 8 a.m. to 12 p.m.
• Rejection Criteria: Hemolyzed sample, lipemic sample, sample containing a separating gel, or sample with insufficient volume

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• Positive: indicates an active or subclinical autoimmune process, even before T4 levels drop.

• Negative: does not rule out hypothyroidism, since not all cases have detectable antibodies.

• Important in screening and early diagnosis programs.

Test Method
Enzyme-Linked Immunosorbent Assay (ELISA).

Test description: Assessment of the therapeutic response to levothyroxine administration by measuring baseline total T4 (before administration) and post-pill total T4 (4–6 hours after administration).
Comments: Indicated for monitoring dogs undergoing treatment for hypothyroidism, allowing for dose adjustment and evaluation of therapeutic efficacy.

• Sample type: Serum
• Species: Canine and Feline
• Optimal volume: 0.7 mL per cycle
• Minimum volume: 0.5 mL per cycle
• Container: Tube with a red or yellow cap, without a gel separator
• Fasting: 8 a.m. to 12 p.m.
• Rejection Criteria: Samples without a collection time, hemolyzed, lipemic, or of insufficient volume

• Low baseline T4 and adequate post-pill T4: satisfactory therapeutic response.

• Low post-pill T4: may indicate an insufficient dose, poor absorption, or improper administration.

• Very high post-pill T4: suggests an excessive dose.

Test Method
Radioimmunoassay (RIA).

Test description: Combined panel that measures free T4 by equilibrium dialysis (ED) and canine TSH (CLIA).
Comments: Considered one of the most robust combinations for diagnosing hypothyroidism, combining the high specificity of canine TSH with the sensitivity of free T4 by dialysis.

• Sample type: Serum
• Species: Canine and Feline
• Optimal volume: 1.4 mL (0.7 mL per test)
• Minimum volume: 1.0 mL (≥0.5 mL per test)
• Container: Tube with a red or yellow cap, without a gel separator
• Fasting: 8 a.m. to 12 p.m.
• Rejection Criteria: Hemolyzed sample, lipemic sample, sample containing a separating gel, or sample with insufficient volume

• Elevated TSH + low free T4: a diagnosis highly suggestive of hypothyroidism.
• Normal TSH + low free T4: does not rule out hypothyroidism, but may reflect a non-thyroidal illness.
• Elevated TSH + normal free T4: may indicate early-stage thyroid dysfunction.

Test description: Panel combining total T4 (RIE) and free T4 by equilibrium dialysis (RIE).
Comments: A combination used to provide a comprehensive view of thyroid function, allowing for the detection of reductions in total T4 as well as the confirmation of specific changes in the free fraction (T4L).

• Sample type: Serum
• Species: Canine and Feline
• Optimal volume: 1.4 mL (0.7 mL per test)
• Minimum volume: 1.0 mL (≥0.5 mL per test)
• Container: Tube with a red or yellow cap, without a gel separator
• Fasting: 8 a.m. to 12 p.m.
• Rejection Criteria: Hemolyzed sample, lipemic sample, sample containing a separating gel, or sample with insufficient volume

• Low total T4 + low T4LDE: diagnosis of hypothyroidism.

• Low total T4 + normal T4LDE: suggests a non-thyroidal illness (sick-euthyroid syndrome).

• Normal total T4 + low T4LDE: may indicate the onset of thyroid dysfunction or antibody interference with T4T.

Test Method
Radioimmunoassay (RIA).

Test description: Panel that measures total thyroxine (T4T) and canine thyroid-stimulating hormone (cTSH) on the Immulite 2000 platform.
Comments: A practical combination for initial screening of thyroid function. Joint interpretation improves accuracy compared to using each test in isolation.

• Sample type: Serum
• Species: Canine and Feline
• Optimal volume: 1.4 mL (0.7 mL per test)
• Minimum volume: 1.0 mL (≥0.5 mL per test)
• Container: Tube with a red or yellow cap, without a gel separator
• Fasting: 8 a.m. to 12 p.m.
• Rejection Criteria: Hemolyzed sample, lipemic sample, sample containing a separating gel, or sample with insufficient volume

• Low T4T + elevated TSH: suggestive of hypothyroidism.

• Low T4T + normal TSH: may indicate sick euthyroid syndrome.

• Normal T4 and T5 + elevated TSH: may indicate the onset of hypothyroidism.

Test Method
Chemiluminescent Immunoassay (CLIA – Immulite 2000 XPI).

Test description: Panel combining free T4 (CLIA – Immulite 2000) and canine TSH (CLIA).
Comments: Provides a practical overview of thyroid function, although it is more susceptible to interference from binding proteins and antibodies than equilibrium dialysis.

• Sample type: Serum
• Species: Canine and Feline
• Optimal volume: 1.4 mL (0.7 mL per test)
• Minimum volume: 1.0 mL (≥0.5 mL per test)
• Container: Tube with a red or yellow cap, without a gel separator
  
• Fasting: 8 a.m. to 12 p.m.
• Rejection Criteria: Hemolyzed sample, lipemic sample, sample containing a separating gel, or sample with insufficient volume

• Low T4L 2000 + elevated TSH: strongly suggestive of hypothyroidism.

• Low T4L 2000 + normal TSH: may indicate a systemic non-thyroidal disease.

• Normal T4L 2000 + elevated TSH: may indicate early-stage hypothyroidism.

Test Method
Chemiluminescent Immunoassay (CLIA – Immulite 2000 XPI).

Test description: Basic profile for thyroid function screening, including canine TSH and total T4 (CLIA).
Comments: Recommended as an initial evaluation in cases of suspected hypothyroidism; more affordable than comprehensive panels.

• Sample type: Serum
• Species: Canine and Feline
• Optimal volume: 1.4 mL (0.7 mL per test)
• Minimum volume: 1.0 mL (≥0.5 mL per test)
• Container: Tube with a red or yellow cap, without a gel separator
• Fasting: 8 a.m. to 12 p.m.
• Rejection Criteria: Hemolyzed sample, lipemic sample, sample containing a separating gel, or sample with insufficient volume

• Low T4T + elevated TSH: a diagnosis suggestive of hypothyroidism.

• Low T4T + normal TSH: may occur in patients with concomitant non-thyroidal conditions.

• Normal T4 and T5 + elevated TSH: may indicate early-stage thyroid dysfunction.

Test Method
Chemiluminescent Immunoassay (CLIA – Immulite 2000 XPI).

Test description: A screening panel developed by Hormonalle that combines canine TSH (CLIA), total T4 (CLIA), and free T4 by equilibrium dialysis (EDD).
Comments: Enables expanded screening by combining the convenience of CLIA (TSH and T4T) with the high sensitivity and specificity of T4LDE, considered the gold standard.

• Sample type: Serum
• Species: Canine and Feline
• Optimal volume: 2.1 mL (0.7 mL per test)
• Minimum volume: 1.5 mL (≥0.5 mL per test)
• Container: Tube with a red or yellow cap, without a gel separator
• Fasting: 8 a.m. to 12 p.m.
• Rejection Criteria: Hemolyzed sample, lipemic sample, sample containing a separating gel, or sample with insufficient volume

• Elevated TSH + low free T4 and total T4: a diagnosis highly suggestive of hypothyroidism.
• Low T4T + normal T4LDE: indicates sick euthyroid syndrome.
• Normal TSH + low free T4: may indicate a concomitant disease or the onset of dysfunction.

Test description: Standard thyroid panel including free TSH, total T4, free T4 (Immulite 2000), and anti-thyroglobulin antibody (TGAA).
Comments: Provides a comprehensive assessment of thyroid function by combining hormonal markers (CLIA) with the immunological profile (EIE).

• Sample type: Serum
• Species: Canine and Feline
• Optimal volume: 2.8 mL (0.7 mL per test)
• Minimum volume: 2.0 mL (≥0.5 mL per test)
• Container: Tube with a red or yellow cap, without a gel separator
• Fasting: 8 a.m. to 12 p.m.
• Rejection Criteria: Hemolyzed sample, lipemic sample, sample containing a separating gel, or sample with insufficient volume

• Low T4 + high TSH: hypothyroidism.
• Low T4 + normal TSH: may occur in non-thyroidal illness.
• Positive TGAA: indicates autoimmune lymphocytic thyroiditis, even in the early stages.

Test description: Comprehensive hormonal panel combining CLIA-based hormone testing, free T4 by equilibrium dialysis (EDD), and anti-thyroglobulin antibody (TGAA – EIA).
Comments: This is the most comprehensive test in the thyroid panel, combining hormone measurements, free fraction by reference method, and immunological assessment for greater diagnostic accuracy.

• Sample type: Serum
• Species: Canine and Feline
• Optimal volume: 2.8 mL (0.7 mL per test)
• Minimum volume: 2.0 mL (≥0.5 mL per test)
• Container: Tube with a red or yellow cap, without a gel separator
• Fasting: 8 a.m. to 12 p.m.
• Rejection Criteria: Hemolyzed sample, lipemic sample, sample containing a separating gel, or sample with insufficient volume

• Elevated TSH + low T4T and T4LDE: strong diagnosis of hypothyroidism.
• Low T4T + normal T4LDE: suggests sick euthyroid syndrome.
• Positive TGAA: confirms an autoimmune process; useful for early diagnosis and follow-up.

Test description: Measurement of total thyroxine (T4T) in serum following administration of levothyroxine.

Comments: Intended exclusively for monitoring levothyroxine replacement therapy in dogs with hypothyroidism. The sample should be collected at the peak of the drug’s action, generally between 4 and 6 hours after oral administration (unless otherwise clinically indicated).

The purpose of the test is to determine whether the administered dose is appropriate, thereby preventing underdosing or overdosing.

• Sample type: Serum
• Species: Canine
• Recommended volume: 0.7 mL
• Minimum volume: 0.5 mL
• Container: Tube with a red or yellow cap
• Rejection Criteria: Hemolyzed sample, marked lipemia, or insufficient volume

Serum concentrations should be measured based on the exact time of collection following medication administration.

Values below the expected peak may indicate underdosing, a failure in administration, or malabsorption.

Persistently elevated levels may indicate an overdose and a risk of iatrogenic thyrotoxicosis.

Results should always be interpreted in conjunction with clinical signs and therapeutic response.

The following substances interfere with the test: glucocorticoids, phenobarbital, bromide, and sulfonamides.

Test Method

Radioimmunoassay (RIA)

Test description: Serum total thyroxine (T4T) measurement following administration of levothyroxine, performed using an automated method.

Comments: Indicated for monitoring levothyroxine replacement therapy. The sample should preferably be collected between 4 and 6 hours after oral administration of the medication, unless otherwise specified by the attending veterinarian.

It enables therapeutic monitoring using a highly reproducible methodology.

• Sample type: Serum
• Species: Canine
• Recommended volume: 0.7 mL
• Minimum volume: 0.5 mL
• Container: Tube with a red or yellow cap
• Rejection Criteria:
  Hemolyzed sample, marked lipemia, presence of separating gel, or insufficient volume

The interpretation must take into account the exact time of administration and collection.

Values below the therapeutic range at peak concentration suggest a dose adjustment.

High levels may indicate excessive hormone replacement.

The following substances interfere with the test: glucocorticoids, phenobarbital, bromide, and sulfonamides.

Clinical evaluation remains essential for treatment decisions.

Test Method

Chemiluminescent Immunoassay (CLIA) – Immulite 2000

Test description: Assessment of the therapeutic response to levothyroxine administration by measuring baseline total T4 (pre-medication) and post-pill total T4 (4–6 hours after administration) using an automated method.

Comments:

Intended for monitoring dogs undergoing treatment for hypothyroidism, allowing for precise dose adjustment and assessment of therapeutic efficacy. The baseline sample should be collected immediately before administration of levothyroxine.
The second sample should be collected between 4 and 6 hours after oral administration, a time frame corresponding to the expected serum peak.

• Sample type: Serum
• Species: Canine
• Optimal volume: 0.7 mL per cycle
• Minimum volume: 0.5 mL per cycle
• Container: Tube with a red or yellow cap.
• Rejection Criteria: Samples without identification of the time of collection (pre- and post-), hemolyzed samples, samples with marked lipemia, or samples with insufficient volume

Low baseline T4 and post-pill T4 within the expected therapeutic range: Satisfactory therapeutic response.

Low post-pill T4: May indicate insufficient dose, malabsorption, or improper administration.

Very high post-pill T4: Suggests an excessive dose, with a risk of iatrogenic thyrotoxicosis.

The interpretation should always take into account clinical signs, the patient’s clinical course, and potential drug interactions (glucocorticoids, phenobarbital, bromide, sulfonamides).

Test Method

Chemiluminescent Immunoassay (CLIA) – Immulite 2000