Hyperthyroidism in cats can be one of the simpler diagnoses made by veterinarians. When a geriatric cat is showing signs of weight loss, increased appetite, and hyperactivity, the veterinarian simply needs to test for elevated T4 levels to confirm that the patient is hyperthyroid. But what happens when the disease is not as straightforward?
Understanding Feline Hyperthyroidism
It is common for older cats to have concurrent illnesses such as renal disease, cancer, or enteropathy. Non-thyroidal illness can also artificially decrease T4 levels. In fact, 10% of hyperthyroid cats and more than 30% of cats with early thyroid disease will have a normal T4. In these cases, further diagnostics should be performed to obtain a definitive diagnosis.
The Role of TSH in Thyroid Diagnostics
TSH is the most utilized hormone for diagnosis of thyroid disease in humans but is not as widely performed in veterinary medicine. However, this hormone can give us a lot of information about the status of thyroid function. Due to the negative feedback mechanism of the body, decreased concentrations of TSH indicate that there is an excess of circulating thyroid hormone. Theoretically, TSH could be a great confirmatory test for hyperthyroidism in cats, because it allows us to look at the function of the feedback loop. Historically, the only option for testing TSH has been a chemiluminescent canine assay that can only measure TSH values as low as 0.03 ng/mL. Studies have shown that while cats with undetectable TSH are more likely to be diagnosed as hyperthyroid within a couple years, there are some normal cats with TSH levels lower than 0.03 ng/mL. Therefore, current TSH testing lacks some specificity for diagnosing the disease.
Feline-Optimized TSH Enhances Patient Care
The TRUFORMA In-Clinic Biosensor Testing Platform offers the first and only feline-optimized TSH, changing how we can diagnose and monitor thyroid disease in cats. Using Bulk Acoustic Wave (BAW) technology, TRUFORMA’s feline optimized TSH assay achieves a lower limit of quantification (LLOQ) far below the chemiluminescent assay, at 0.008 ng/mL. This makes TRUFORMA’s assaymore sensitive and specific for diagnosis of hyperthyroidism and thus allows veterinarians to better distinguish between normal cats and hyperthyroid cats. In cats with borderline elevated or high-normal T4 levels due to non-thyroidal illness or early disease, feline-optimized TSH is an excellent confirmatory test.
Validating TRUFORMA's Feline-Optimized TSH Assay
A 2024 study performed by Dr. Mark Peterson, a leading veterinary endocrinology specialist, validates and compares the TRUFORMA feline-optimized TSH assay to the traditional chemiluminescent method used at reference laboratories. It found that because of the very low values that the TRUFORMA assay can detect, veterinarians can diagnose hyperthyroidism earlier in the disease process as well as in cases of subclinical disease. This can lead to the patient receiving treatment sooner, before much of the damage to other body systems occurs.
Screening and Early Detection
TRUFORMA’s feline-optimized TSH assay can also be used as a routine screening test for geriatric felines, the same way we often screen for T4 in these patients. One study found that TSH levels less than 0.03 ng/ml were associated with an increased likelihood of hyperthyroid diagnosis within 14 months. This suggests the assay can be used as a biomarker to determine future risk of disease.
Monitoring Hyperthyroidism Using Feline-Optimized TSH
Screening for and definitively diagnosing hyperthyroidism are not the only utilizations of the TRUFORMA TSH assay. Cats undergoing treatment for hyperthyroidism are at risk of developing iatrogenic hypothyroidism, which can cause a decline in renal function. An elevated TSH in these patients indicates that circulating thyroid hormone levels are too low, and a dosage adjustment or hormone supplementation is needed.
Treating Hyperthyroidism Using Feline-Optimized TSH and Radioactive Iodine
It has also been suggested that TSH testing should be performed prior to administration of radioactive iodine as a treatment for hyperthyroidism. TSH levels greater than 0.03 ng/ml can indicate that the patient is more at risk of developing iatrogenic hypothyroidism after I131 therapy. It is recommended to wait to treat these patients until TSH levels have decreased below 0.03 ng/ml. If that is not possible, they should receive a lower dose of I131.
The Future is Bright with TRUFORMA’s Feline-Optimized TSH Assay
Every veterinarian has heard the adage “cats are not small dogs”. Having access to TRUFORMA’s feline-optimized TSH assay gives vets a better way to screen, diagnose, and monitor cats with hyperthyroidism – the most common endocrinopathy of the feline population. By diagnosing these patients sooner and being able to monitor their therapy closer, we can improve the quality of life for cats and their owners.
