LUC (large unstained cells) in cats and dogs
LUC, large unstained cells, is a line printed by hematology analyzers that sort white cells with a peroxidase stain. It collects large cells that take up little of that stain. According to the Cornell diagnostic laboratory, these are large or reactive lymphocytes, monocytes or leukemic blasts — in most animals mostly large lymphocytes or monocytes.
What it shows
Some laser-based analyzers, such as the ADVIA, stain white cells for peroxidase — an enzyme found in the granules of neutrophils and eosinophils — and sort them by size and by how strongly they stain. Each usual cell type lands in its own cluster on the machine’s plot, and from these clusters the analyzer builds an automated differential.
Cells that are large but carry little peroxidase do not fit the usual clusters and are reported separately as LUC. In most animals these are mostly large lymphocytes or monocytes; reactive lymphocytes — cells changed by an immune response — land here too. So LUC is not a cell type but a label for large cells the machine could not place more precisely, a bit like a “miscellaneous” shelf.
Higher than reference — what it may be a sign of
- Immune stimulation — reactive lymphocytes appear in the blood in response to antigens. Any disease process can cause this, so the finding is not specific; it is seen more often in young animals.
- More large monocytes — inflammation, infectious or not; in dogs also stress.
- Abnormal cells — telling reactive lymphocytes from tumour cells is a job for an experienced clinical pathologist looking at a smear; when cells cannot be identified, the vet may suggest repeat testing and a check for blood cancers.
- Sample problems — old samples and samples with many platelet clumps can make the automated differential inaccurate.
Lower than reference
The sources describe no clinical meaning for a low LUC; this line matters mainly when it rises. A value of zero or close to it is usually read simply as “no unusual large cells counted”, and the vet looks at the rest of the leukogram.
Look at together with
- Lymphocytes and monocytes — the cell types LUC is usually made of; a rise in LUC with them points in the same direction.
- Total white cell count (WBC) — needed to turn the percentage into an absolute number.
- Neutrophils — inflammation usually shows on them first.
- Analyzer flags and the blood smear — the lab flags the automated differential when something looks unusual and recommends a smear; only the smear shows what the large cells are.
Units and conversion
The absolute count (LUC) is reported as ×10⁹/L (×10^9/л on Russian-language forms); the factor is 1. The percentage (LUC%) is the share of large unstained cells among all white cells. Absolute count = percentage × WBC ÷ 100. As with other white cells, a vet relies on the absolute count: a percentage means little without the total. In the app each row keeps the unit printed on the form.
Reference range
The reference range is on your lab’s form. LUC exists only on analyzers of this type, and the Cornell laboratory notes that its automated differential intervals apply only to automated counts — they cannot be compared with a manual differential. The same laboratory reports that automated counts agree well with manual ones for neutrophils and lymphocytes, but weakly for monocytes and poorly for basophils. So a LUC outside the range is a reason to look at the smear, and a trend across tests from the same lab says more than one value.
Cats and dogs
The sources describe no separate feline rules for LUC; it is read as in dogs. In cats peroxidase-based counts have their own pitfalls: platelet clumps can raise the white cell count, and in rare cats with Heinz bodies in more than half of the red cells the white cell count on one channel of the analyzer can be falsely high. Unusual results in a cat are therefore checked on a smear.
In greyhounds, other sighthounds and Golden Retrievers some eosinophils lack visible granules and contain less peroxidase; on the ADVIA they drift into the monocyte cluster. This is a good example of why peroxidase-based sorting depends on what the cells contain, and why a vet confirms an unexpected automated differential in a dog on a smear.
Add a lab form — Pet Tracker Space recognises the lines, keeps the form’s units and draws each indicator over time with your lab’s reference band.
Sources
- Cornell University Animal Health Diagnostic Center — Hematology testing protocols
- Cornell University Animal Health Diagnostic Center — Reference intervals: Hematology (Advia 2120)
- eClinPath (Cornell University) — WBC counts
- eClinPath (Cornell University) — Normal leukocytes
- eClinPath (Cornell University) — Reactive lymphocytes
- eClinPath (Cornell University) — Individual WBC
This page explains what a lab value means. It is not a diagnosis and not a substitute for your veterinarian — only they can interpret results for your pet.