A degenerative left shift (DLS) describes a neutrophil pattern in which there are a larger number of immature granulocytic precursors as compared to mature neutrophils. In cats, bone marrow has a large storage reserve of neutrophils. When the demand for neutrophils exceeds this reserve, the bone marrow releases granulocytic precursors into the blood circulation, resulting in DLS.
This retrospective case-control study of 108 cats with DLS and 322 control cats presenting to a veterinary hospital sought to determine if cats presenting with DLS had an increased risk of euthanasia or death. Disease categories included septic peritonitis, pyothorax, FeLV, wounds, and other. The authors found that cats diagnosed with DLS were 1.57 times more likely to die or be euthanized in hospital when compared to control cats with the same disease. In addition, cats with increased DLS severity were at increased risk for death or euthanasia.
The main conclusion of this retrospective study was that cats presenting to a veterinary medical teaching hospital with a DLS were 1.57 times more likely to die (or be euthanized) in hospital than cats with the same diseases without a DLS. This conclusion should not be over-interpreted, however, because cases were analyzed from medical records created over 15 years. Problems that could arise from such an analysis are variations in technician and pathologist interpretation of cell morphology, possibly incurring misclassification of cells. In addition, the study parameters did not include CBC findings that were collected at any time other than within 24 hours of admission. It is, therefore, a snapshot-in-time that might overlook improvement in the left shift that occurred subsequently, possibly even resolving. Although nice to have for prognostication, because each patient can respond differently, hazard ratios should not be oversold to clients, as doing so can result in earlier death.—Margie Scherk, DVM, DABVP (Feline)
Degenerative left shift as a prognostic tool in cats. Burton AG, Harris LA, Owens SD, Jandrey KE. J VET INTERN MED 28:912-917, 2014.