Lymphocytosis
VeDDRA Code: 165
1,027 adverse event reports referencing this reaction
Species Most Affected
Breeds Most Affected
Associated Drugs
Data Summary
| Metric | Value |
|---|---|
| Total reports referencing reaction | 1,027 |
| Reports with fatal outcome | 245 |
| Case-fatality rate (reported events) | 2390.0% |
| Species observed | 5 |
| Breeds observed | 20 |
| Drugs associated with reaction | 20 |
Source: FDA Center for Veterinary Medicine — Adverse Event Reporting (CVM AER); reaction term coded under VeDDRA 165.
Lymphocytosis Reaction Insights
The FDA Center for Veterinary Medicine database currently lists 1,027 adverse event reports that reference Lymphocytosis as a reaction term, including 245 reports with a death outcome — a 2390.0% case-fatality figure calculated across only those events where this reaction was coded. The reaction is indexed in the openFDA system under VeDDRA code 165, the standardized veterinary dictionary used to normalize clinical signs across submitters. Because reports are voluntary and often describe multiple concurrent signs per animal, the volume here reflects reporting intensity rather than true incidence in the broader pet population.
Lymphocytosis appears most frequently in reports for Dog (853 reports), Cat (162 reports), Horse (8 reports) — with Dog dominating at 853 entries. Within those species, the breeds most often named alongside this reaction are Domestic Shorthair (109), Retriever - Labrador (95), Retriever - Golden (70). These distributions are influenced both by underlying breed popularity and by how veterinarians and owners code a given clinical sign, so they should be interpreted as a reporting fingerprint rather than a pure susceptibility ranking.
The drugs most commonly co-reported with Lymphocytosis are Milbemycin Oxime + Spinosad (123 reports), Afoxolaner (103 reports), Maropitant Citrate (90 reports), Carprofen (72 reports), with Milbemycin Oxime + Spinosad appearing alongside this reaction in 123 submissions. Co-reporting does not establish that any specific product caused the reaction — FDA CVM data captures temporal association only. The value of these aggregates is in flagging which therapeutic classes appear repeatedly alongside a given clinical sign, so owners and veterinarians can ask targeted questions about medications currently in use.
Source: FDA Center for Veterinary Medicine — Adverse Event Reports FDA Center for Veterinary Medicine — Adverse Event Reports Data reflects voluntary submissions and may not represent actual incidence rates
Read our methodology — how this data is sourced, computed, and verified.