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Phenol Red Thread Test

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Sourced from published veterinary references. Awaiting credentialed clinical reviewer — our editorial process.

Drug Class

Diagnostic

Routes

TOPICAL (ophthalmic)

Indications

Tear production measurement

Mechanism of Action

pH-sensitive dye thread placed in lower conjunctival fornix. Tears change thread color from yellow to red, measuring tear production in 15 seconds.

Side effects & warnings

Less invasive than Schirmer tear test. Good for exotic species and cats. Normal values differ by species. Not a therapeutic agent.

Species with Phenol Red Thread Test dosing data (2 dose rules)

Cat (Domestic)Dog (Domestic)

Species references:All Cat (Domestic) drugsAll Dog (Domestic) drugs

Evidence levels across 2 dose rules

Moderate×2

Each ExoticRx dose rule is graded by the strength of its primary evidence — see the editorial process.

Backed by a published source

  • · Plumb's Veterinary Drug Handbook, 9th Ed

Sample dosing (2 of 2 cited rules)

A dog/cat sample is shown here. Cited dosing for all 2 species — reptiles, birds, pocket pets, livestock, and equine — is free on the per-species pages above. Pro adds the weight-based calculator for every species.

SpeciesRouteDoseFrequencyEvidenceSource
Dog (Domestic)TOPICAL (ophthalmic)0 1 thread per eyePRN (diagnostic)ModeratePlumb's Veterinary Drug Handbook, 9th Ed
Cat (Domestic)TOPICAL (ophthalmic)0 1 thread per eyePRN (diagnostic)ModeratePlumb's Veterinary Drug Handbook, 9th Ed

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