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Objective: To determine the value of a commercially available test for measurement of luteinizing hormone (LH) concentrations for its use in distinguishing between ovariectomized and sexually intact bitches., Design: Prospective longitudinal cohort study., Animals: 101 sexually intact bitches and 199 ovariectomized bitches, Procedure: A commercial test kit was used to assay serum samples for LH concentration. A kappa test was used to assess the consistency of test interpretations. Sensitivity, specificity, predictive values, and consistency of test interpretation in the sample population and in 2 theoretical populations of bitches with differing frequencies of ovarian removal were determined., Results: The test had excellent sensitivity (98%) but moderate specificity (78%) because of a high frequency of false-positive test results. This means that a single high serum LH concentration was not a reliable indicator of ovarian removal. However, a single low serum LH concentration was an excellent indicator that a bitch was sexually intact. The LH test results were positive within 10 days after ovarian removal and remained high in bitches from which ovaries had been removed > 5 years previously. Analysis of kappa values consistently revealed excellent agreement in test interpretation within and among evaluators and over a 6-hour time span., Conclusions and Clinical Relevance: A single low LH test result confirms the need for ovariectomy in bitches prior to adoption. The test is applicable to bitches that have been ovariectomized prior to puberty and probably applies over the lifespan of the animal.