ecallenHow TRUFORMA’s Feline-Optimized TSH Test Prevented Unnecessary Treatment
A Case Study by Kristin Marzin, DVM
Accurate thyroid testing is crucial for feline health, but traditional methods can sometimes lead to misdiagnosis. This case study highlights how TRUFORMA’s innovative feline-optimized TSH test played a pivotal role in preventing unnecessary treatment and ensuring proper patient care.
History and Physical Examination Findings
At the Oregon Veterinary Specialty Hospital’s Feline Radioiodine Center, a neutered 6-year-old male domestic shorthair feline presents with suspected hyperthyroidism. Upon examination, the patient was noted to be overweight, with a body condition score (BCS) of 7/9. They have also gained weight over the past couple of years. While at the time of the first visit the patient is asymptomatic, they have a history of:
- Emergency room visit two years prior for hypersalivation, agitation, and polydipsia
- Elevated total T4 (5.0 mcg/dl) found at ER visit
- Persistent elevation of total T4 in subsequent wellness visits
The patient’s littermate had the same presentation to the ER and bloodwork also indicated a T4 elevation, but he had additional signs of hyperthyroidism and therefore was treated with methimazole. Considering the mild starting total T4 value, higher doses than expected of methimazole were required to lower the normal range by the primary veterinarian. The littermate was then treated with I131, but there was concern that this may not have been curative, as total T4 improved but remained elevated despite positive clinical response. Scintigraphy is not available in the state of Oregon and could not be pursued for either patient.
Diagnostic Findings and Interpretation
At the time of the ER visit, the only abnormal lab finding for the patient was elevated total T4 (5.0 mcg/dl, reference range 0.8-4.7 mcg/dl).
At subsequent visits in the next couple of years, the T4 remained slightly elevated at 4.8 mcg/dl and 4.4 mcg/dl (reference range 0.8-4.0 mcg/dl). At one of these time points (total T4 4.4 mcg/dl), the free T4 measured >100 (reference range 10-50). The patient gained weight and maintained an overweight body condition after the ER visit. At these visits, there were no other significant laboratory findings.
Thyroid Testing at the Feline Radioiodine Center
On presentation to Dr. Decker, additional thyroid testing was performed.
- Total T4 remained elevated at 5.7 mg/dl (reference range 0.8-4.4 mcg/dl).
- A feline-optimized TSH performed using the TRUFORMA Diagnostic System was within normal limits at 0.016 ng/ml (reference range 0.01-0.3 ng/ml).
- A free T4, T3, and chemiluminescent canine TSH were also all within normal limits.
Expert Interpretation of Feline Thyroid Test Results
With the patient’s lack of clinical signs and all laboratory testing other than total T4 showing normal results, it was suggested that the patient’s elevation in total T4 was either spurious or normal for this patient. Since the patient had such a long history of reliably high total T4 values, Dr. Decker concluded that the elevation in T4 was likely a normal variation for this patient, and he was not diagnosed as hyperthyroid. Since the patient’s littermate had exhibited similar lab work and did not respond well to medical management for hyperthyroidism, it was suggested that this could be an inherited anomaly.
Treatment and Outcome
No treatment was initiated for this patient. Dr. Decker recommended the patient return for routine thyroid monitoring every 6-12 months, or sooner if clinical signs develop. Thyroid monitoring tests would include a total T4, feline-optimized TSH, T3, and free T4.
“It is important to treat the cat and not just the number, but be sure you are getting the best numbers possible,” Dr. Decker stated upon conclusion of this case. This can be achieved by thorough thyroid testing, which should include TRUFORMA’s feline-optimized TSH assay.
Reflecting on a Complex Thyroid Case
This case shows the importance of thyroid testing in cats beyond just a total T4. Initiating therapy for hyperthyroidism in this case could have had potentially dangerous effects for the patient since he is not truly hyperthyroid. A feline-optimized TSH, only able to be performed on the TRUFORMA system, helped Dr. Decker reach the appropriate diagnosis and clinical decision for this patient, and will allow her to monitor him closely in the event he truly becomes hyperthyroid.
