Variability of estradiol concentration in normal dogs

Area of Science:

• Veterinary Endocrinology
• Canine Health
• Diagnostic Biomarkers

Background:

• Estradiol measurements are crucial for diagnosing canine endocrine disorders, including atypical Cushing's syndrome.
• Elevated estradiol concentrations in dogs frequently occur without apparent clinical signs of hyperestrogenism, creating diagnostic uncertainty.
• The variability and clinical significance of serum estradiol concentrations in normal dogs remain poorly understood.

Purpose of the Study:

• To quantify the intra- and inter-individual variability of serum estradiol concentrations in healthy, neutered dogs.
• To establish reference ranges for estradiol in a normal canine population.
• To inform the diagnostic interpretation of elevated estradiol levels in canine endocrine testing.

Main Methods:

• Ten healthy, neutered dogs (male and female) were enrolled.
• Serum samples were collected from each dog at 2-hour intervals, four times daily.
• Blood sampling was repeated across three time points: baseline, week 2, and week 6, to assess temporal variations.

Main Results:

• Serum estradiol concentrations exhibited a wide range (44.6–120.3 pg/mL), with a mean of 70.4 pg/mL, often exceeding the laboratory's upper normal limit (69 pg/mL).
• Significant within-dog variability was observed, with mean differences between highest and lowest concentrations ranging from 12.5 to 53.5 pg/mL.
• Mean estradiol concentrations decreased significantly from week 1 (71.4 pg/mL) and week 2 (76.5 pg/mL) to week 6 (63.2 pg/mL).

Conclusions:

• Serum estradiol concentrations in dogs display substantial variability, both within individual dogs and between different dogs.
• Measured estradiol levels frequently surpass established laboratory normal ranges, highlighting the need for careful interpretation.
• Diagnosis of hyperestrogenism or atypical Cushing's syndrome should integrate clinical signs with elevated serum estradiol results.