Cushing's pretest score

Structured pretest probability score for canine hyperadrenocorticism. Weights clinical signs and laboratory findings to triage patients into low / moderate / high pretest probability before endocrine testing.

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Clinical background

Hyperadrenocorticism (HAC; Cushing’s disease) is one of the most commonly suspected and most overdiagnosed endocrine diseases in dogs. The clinical signs (PU/PD, polyphagia, abdominal distension, alopecia, panting, muscle weakness) are individually nonspecific and overlap heavily with other diseases (diabetes mellitus, primary kidney disease, atypical liver disease, and simple obesity). The cumulative pretest probability of HAC determines whether further endocrine testing is appropriate, and crucially, how to interpret the results.

Why a pretest score matters

The two principal screening tests for HAC, the LDDST and the urine cortisol:creatinine ratio, both have meaningful false-positive rates in dogs that are stressed, sick with non-adrenal disease, or recently treated with corticosteroids. The ACTH stimulation test has a false-negative rate that increases with PDH severity. None of these tests is reliable in a low-pretest-probability dog: a positive result in a dog without convincing clinical signs is more likely to be a false positive than true HAC.

Conversely, in a dog with multiple convincing clinical signs and supporting laboratory abnormalities, the pretest probability is high enough that even a borderline test result is meaningful, and any negative result should prompt re-testing rather than ruling out the disease.

How the InfusionFox score works

The score weights findings by how strongly each one shifts the pretest probability based on published clinical experience:

• Highly suggestive findings (PU/PD, polyphagia, pendulous abdomen, alopecia, persistent panting, dermatologic signs), each adds points
• Common but less specific findings (lethargy, muscle weakness, recurrent infections), fewer points
• Supporting laboratory findings (elevated ALP, stress leukogram, dilute urine, mild proteinuria), small contribution
• Discriminating findings (hypertension, calcinosis cutis), strong evidence

The numerical score sorts patients into categories, low, moderate, high pretest probability, that drive the interpretation of subsequent testing. The score is not diagnostic on its own: it’s a clinical communication tool to help decide whether endocrine testing is appropriate, and how to interpret the results.

How to use the score in practice

1. Low pretest score → reconsider the differential diagnosis. Investigate alternative causes of the presenting signs. Endocrine screening is unlikely to be helpful and is more likely to mislead than diagnose.
2. Moderate pretest score → screening is appropriate. Choose between LDDST and UCCR based on cost, availability, and patient stress level. A positive result supports the diagnosis; a negative result largely rules it out.
3. High pretest score → screening is essentially confirmatory. A positive result confirms HAC; a negative result should prompt repeat testing (false negatives are more likely than no disease).

The downstream confirmatory test (LDDST is most informative because it can also discriminate PDH from AT in some cases) and adrenal imaging follow once HAC is supported by initial screening.

Limitations

• The score reflects clinical judgment, not strict statistical validation against a reference standard. Use it as a structured way to record your impression, not a substitute for it.
• A high score in a young dog (under 6 years) should prompt extra caution: HAC is rare in young dogs, and the same clinical signs in that age group are more likely to reflect another disease.
• The score does not replace exclusion of iatrogenic HAC. Always confirm there has been no recent topical, ophthalmic, otic, or systemic glucocorticoid administration before pursuing endocrine testing.

Sources

• Behrend EN et al: Diagnosis of spontaneous canine hyperadrenocorticism: 2012 ACVIM Consensus Statement. J Vet Intern Med 2013;27:1292–1304.
• Bennaim M et al: Clinical and laboratory features in dogs with hyperadrenocorticism. J Vet Intern Med 2018.
• Behrend EN: Canine and Feline Endocrinology, 4th ed., Elsevier, 2015.