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Haematological Tracking of Thyroid Status During Methimazole Therapy and After Treatment Interruption in Hyperthyroid
Andrei Răzvan Codea1, Alexandra Biriș1, Sidonia Gog-Bogdan2
1Department of Internal Medicine, Faculty of Veterinary Medicine, University of Agricultural Sciences and Veterinary Medicine Cluj-Napoca, Calea Mănăştur 3-5, 400372 Cluj-Napoca, Romania.
Insights
Hematocrit (Hct) and mean corpuscular volume (MCV) can help monitor feline hyperthyroidism treatment. Rising Hct or MCV in treated cats may indicate a loss of therapeutic control, prompting further evaluation.
Area of Science:
- Veterinary Medicine
- Endocrinology
- Internal Medicine
Background:
- Feline hyperthyroidism is a common endocrine disease in older cats.
- Thyroxine (TT4) monitoring is often expensive and inaccessible.
- Alternative monitoring methods are needed for cost-effectiveness.
Purpose of the Study:
- To investigate the correlation between hematocrit (Hct), hemoglobin (Hgb), mean corpuscular volume (MCV), alanine aminotransferase (ALT), and total thyroxine (TT4) in hyperthyroid cats.
- To assess the utility of Hct and MCV as potential indicators of therapeutic control during methimazole treatment.
- To establish cut-off values for Hct to predict treatment response.
Main Methods:
- Prospective study of 43 cats with primary hyperthyroidism.
- Measurements of Hct, Hgb, MCV, ALT, and TT4 at baseline and at 1, 3, and 6 months.
- Statistical analyses included correlations, linear mixed-effects models, and ROC analysis.
Main Results:
- Strong correlations were observed between TT4 and Hct, MCV, Hgb, and ALT, which intensified over time.
- Within-cat analyses showed Hct and MCV tracked TT4 levels during treatment.
- ROC analysis identified Hct ≥ 35.2% at 2 months as an optimal cut-off (AUC=0.972) for predicting treatment status.
Conclusions:
- Hct and MCV can serve as valuable indicators of TT4 levels in hyperthyroid cats undergoing treatment.
- Changes in Hct or MCV may signal a loss of therapeutic control, warranting TT4 re-evaluation.
- These parameters offer a more accessible and cost-effective adjunct to hormonal monitoring.
Abstract:
Background: Feline hyperthyroidism is the most prevalent endocrine disorder of older cats; TT4 monitoring is costly and often inaccessible. Methods: Forty-three cats with primary hyperthyroidism were followed prospectively at baseline (T0) and at 1, 3 and 6 months (T1, T2, T3). Hct, Hgb, MCV, ALT and TT4 were measured at each visit. Per-timepoint correlations, repeated-measures correlation (rmcorr), linear mixed-effects models, and Friedman and ROC analyses were performed. Results: TT4 correlated with Hct (r = 0.875 at T1 to 0.943 at T3), MCV (0.907 to 0.964), Hgb (0.836 to 0.946) and ALT (0.919 to 0.981), intensifying progressively. Within individual cats, Hct (rmcorr r = 0.873) and MCV (rmcorr r = 0.881) tracked TT4, and for Hct, the within-cat coefficient exceeded the between-cat coefficient. All primary parameters and ALT changed significantly from T0 to T1 (all p < 0.001). ROC analysis identified Hct ≥ 35.2% at T2 as the optimal cut-off (AUC = 0.972, 95% CI 0.914-1.000; sensitivity 96.7%, specificity 92.3%). Conclusions: Hct and MCV tracked TT4 within individual cats during methimazole therapy and returned toward pre-treatment values after discontinuation. A rising Hct or MCV in a treated cat may signal loss of therapeutic control and prompt TT4 re-evaluation, without replacing hormonal monitoring.
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