Glomerular filtration rate (GFR) is decreased in human hypothyroid patients, but information about kidney function in canine hypothyroidism is lacking. The objective of this study was to assess GFR in hypothyroid dogs, prior to substitutional therapy and after reestablishment of a euthyroid state.

Hypothyroid dogs (n=14) without gross abnormalities on renal ultrasonography and urinalysis were included. Blood pressure measurement and exogenous serum creatinine clearance (ECC) test were performed before treatment (t0, n=14), one month (t1, n=14) and 6 months (t6, n=11) after supplementing levothyroxine (20µg/kg/day PO) therapy. At t1, response to therapy was monitored by measurement of serum total thyroxine and thyrotropin. If thyroid treatment needed to be adjusted, it was reassessed after one month.

Statistical analysis was performed using a general linear model, results were expressed as mean±SD.

Age at t0 was 6.25±1.4 years, body weight decreased (P<0.05) from 35±18 kg at t0 to 27±14 kg at t6. All dogs remained normotensive throughout the study. Basal serum creatinine also decreased (P<0.05) from 121±37 to 98±20 and 104±28 µmol/L at t0, t1 and t6, respectively. ECC conversely increased (P<0.01), the corresponding values were 1.6±0.4, 2.1±0.4 and 2.0±0.4 mL/min/kg, respectively.

Decreased GFR was observed in hypothyroid dogs. However re-establishment of a euthyroid state increased GFR significantly.

Originally presented at the European College of Veterinary Internal Medicine--Companion Animals Congress, September 2007.