Veterinarians may be required to determine the gonadal status of an animals in circumstances including:
- After desexing surgery to confirm complete removal of gonadal tissue
- Supposedly desexed bitches and queens exhibiting signs of oestrus (confirmation of "ovarian remnant syndrome")
- Suspected cryptorchid males
- Female cats and dogs with unknown desexing history, particularly stray animals
In intact bitches and queens, or those with functional ovarian remnants, baseline LH is low due to negative feedback from ovarian oestradiol. Serum LH will only be elevated at the natural LH peak preceding ovulation. In fully ovariectomised animals, LH is persistently high due to lack of negative feedback control.
A single low LH value indicates that there is functional ovarian tissue present. If a positive (high) value is recorded, the animal must be retested with a new sample at least 2 hrs after original sampling. This is to differentiate a persistently high value (no functional ovarian tissue present) from the transient pre-ovulatory LH peak (functional ovarian tissue present).
Currently there is no published literature supporting the use of the serum LH assay to distinguish fully castrated from intact male dogs or cats. However, one study has confirmed that fully castrated male dogs have higher LH levels than intact animals. Use of the LH test for male dogs is therefore off-label and not validated, and interpretation remains with the veterinarian if requested.
Serum AMH (Anti- Müllerian Hormone) testing is also available and requires a single blood sample only. In-house methods to assess gonadal status include vaginal cytology (which requires the animal to be in oestrus), or ultrasound (which requires an experienced operator, and may miss small ovarian remnants). Serum progesterone or testosterone can be measured, but interpretation can be hampered by naturally fluctuating levels of each, particularly with stage of cycle in females and with cryptorchidism in dogs. Stimulation with gonadotrophs (hCG or GnRH) may be required to demonstrate functional gonadal tissue.
Serum (minimum volume 2 ml)
Plain (red top) tube
Olson PN, Mulnix JA, and Nett TM. (1992) Concentrations of luteinizing hormone and follicle-stimulating hormone in the serum of sexually intact and neutered dogs. Am J Vet Res 53(5):762-6.
Lofstedt RM & Vanleeuwen (2002) Evaluation of a commercially available luteinising hormone test for its ability to distinguish between ovariectomised and sexually intact bitches. JAVMA 220(9):1331-5