Anti-Müllerian Hormone (AMH) is present in males from birth. Testosterone is generally measurable in normal intact males starting at one year of age, though levels are often lower than mature stallion levels. Cryptorchid testicles often produce less testosterone than normal testicles. Estrone sulfate is useful for detecting testicular tissue in males three years of age and older. Our laboratory offers a Cryptorchid Panel which includes measurements of AMH, testosterone and estrone sulfate from a single sample. A high value in any of these hormones indicates the presence of testicular tissue. Equivocal levels should be interpreted with view to clinical signs and the other test results. The hCG-response test is recommended in cases where the Cryptorchid Panel results are indeterminate or if there is any question of exogenous steroid use. 

AMH and estrone sulfate are not available for male donkeys.

Anti-Müllerian Hormone (AMH) 

AMH is produced by sertoli cells in the testicle. It is present at birth in males, so can be used to differentiate cryptorchid from gelded before reproductive maturity. It should be used in combination with testosterone and/or estrone sulfate for possible incomplete castrations.

Testosterone Baseline

The testosterone baseline test is useful to assess functionality in normal stallions. It is primarily used for distinguishing fully castrated males from those with retained testicles or testicular remnants. Cryptorchid testicles often produce less testosterone than normal testicles. For accurate diagnosis it is recommended that the hCG-response test be used initially or as follow up to the testosterone baseline test. Horses should be at least 1 year of age.

Estrone Sulfate Baseline

Mature testicular tissue produces estrone sulfate. Horses should be three years of age or older when using this test for diagnosis of cryptorchism. Appropriate reference ranges for cryptorchid males and stallions have been established for our test. This test can be followed by an hCG-response test to confirm the diagnosis.

hCG-Response Test

The hCG response test is the most reliable test for detecting functional testicular tissue. It is useful for assessing testicular function in breeding stallions. It is also useful for distinguishing fully castrated animals from those with retained testicles or testicular remnants. The response test is more accurate than a single baseline in cryptorchid horses because cryptorchid testicles often produce less testosterone than normal testicles. Testosterone response to hCG should be present, but may be decreased in these animals when compared to normal stallions. This test can clarify equivocal Cryptorchid Panel results.

1. Draw a baseline blood sample as described below.
2. Inject 10,000 IU of hCG (human chorionic gonadotropin) intravenously. For miniature horses, inject 2,500 IU of hCG intravenously.
3. Collect an additional sample 2 hours after hCG injection.

Note: GnRH cannot be substituted for hCG when response testing horses.

Guidelines for Sample Collecting and Processing:

1. Collect blood into a plain red-top collection tube.
2. Allow blood adequate time to clot prior to centrifugation to ensure sufficient yield and avoid fibrin formation.
3. After centrifugation, transfer the serum into a vial suitable for shipping or frozen storage. Frozen sample storage is recommended unless samples are being shipped the day taken.
4. Ship samples with cold packs. A frozen specimen is not necessary, but the sample should arrive chilled.