E
Eccentrocyte
DEFINITION
Erythrocyte damaged by oxidants. Characterized by focal area of fused membranes with eccentric displacement of hemoglobinized cytosol and loss of any central pallor. The collapsed area with fused membranes appears as a clear area at periphery of erythrocyte which is outlined by a barely visible cell membrane.
PHYSIOLOGY
During oxidative damage, hemichromes (oxidized forms of hemoglobin) bind to the band 3 protein of the membrane cytoskeleton. This creates cross-linking and fusion of the erythrocyte cytoskeleton and alters the membrane, with externalizing of antigenic proteins and attachment of autoantibodies. Hemichromes can also precipitate to form Heinz bodies.
CLINICAL APPLICATION
CAUSES OF ABNORMALLY HIGH LEVELS
Ehrlichia Serology
TYPICAL NORMAL RANGE
Reporting differs among reference laboratories. Consult with laboratories for proper interpretation of values.
PHYSIOLOGY
Ehrlichia spp. are rickettsial agents that infect a wide range of host species. Numerous species of Ehrlichia have been shown to infect dogs. E. canis produces an acute disease (canine monocytic ehrlichiosis) from which animals recover, but which typically remains subclinical and may later produce more severe disease. Early (7 days post infection) titers are due to immunoglobulin (Ig)A and IgM; 3 weeks postinfection titers are mostly due to IgG. Most laboratories measure IgG.
CLINICAL APPLICATIONS
CAUSES OF ABNORMALLY HIGH LEVELS
NEXT DIAGNOSTIC STEP TO CONSIDER IF LEVELS HIGH: Evaluate whether the patient’s current signs are consistent with ehrlichiosis, and consider treatment with appropriate antimicrobial therapy. A positive test for ehrlichial DNA via PCR supports active infection and can determine the specific species of Ehrlichia involved.
CAUSES OF ABNORMALLY LOW LEVELS: Infection with different Ehrlichia spp.
NEXT DIAGNOSTIC STEP TO CONSIDER IF LEVELS LOW: If a clinical suspicion for ehrlichiosis persists despite a negative titer to E. canis, titers to other ehrlichial species (e.g., Anaplasma phagocytophilum, formerly E. equi) should be performed, because cross-reactivity does not occur reliably.
SPECIMEN AND PROCESSING CONSIDERATIONS
IMPORTANT INTERSPECIES DIFFERENCES: Serologic tests often use species-specific reagents, and Ehrlichia serologic testing is most often performed on dogs. Check with lab as to appropriateness if testing cats.
PEARLS
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