Effects of blood contamination of cerebrospinal fluid on western blot analysis for detection of antibodies against Sarcocystis neurona and on albumin quotient and immunoglobulin G index in horses.
OBJECTIVE
To determine effects of blood contamination on western blot (WB) analysis of CSF samples for detection of anti-Sarcocystis neurona antibodies, and on CSF albumin and IgG concentrations, albumin quotient (AQ), and IgG index in horses.


METHODS
Prospective in vitro study.


METHODS
Blood with various degrees of immunoreactivity against S neurona was collected from 12 healthy horses. Cerebrospinal fluid without immunoreactivity against S neurona was harvested from 4 recently euthanatized horses.


METHODS
Blood was serially diluted with pooled nonimmunoreactive CSF so that final dilutions corresponded to 10(-3) to 100 microliters of blood/ml CSF, and WB analysis was performed on contaminated CSF samples. Number of RBC, albumin and IgG concentrations, AQ, and IgG index were also determined.


RESULTS
Antibodies against S neurona were detected in CSF contaminated with 10(-3) microliters of strongly immunoreactive blood/ml. In CSF samples contaminated with 10 microliters of blood/ml, AQ remained within reference range. Volume of blood required to increase IgG index varied among blood samples and was primarily influenced by serum IgG concentrations. Number of RBC in contaminated samples was correlated with volume of blood added, but not with degree of immunoreactivity detected in contaminated CSF samples.


CONCLUSIONS
During collection of CSF from horses, contamination with blood may introduce serum antibodies against S neurona at concentrations sufficient for detection by WB analysis, thus yielding false-positive results. When blood is moderately or strongly immunoreactive, the amount of contaminating albumin may be small enough as to not increase AQ above reference range. In these cases, AQ and IgG index should be interpreted with caution.
Department of Clinical Studies, New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square 19348-1692, USA.
M M
MM
Miller
C R
CR
Sweeney
G E
GE
Russell
R M
RM
Sheetz
J K
JK
Morrow
D000418:Albumins / Q000134:cerebrospinal fluid; D000818:Animals; D000913:Antibodies, Protozoan / Q000097:blood / Q000134:cerebrospinal fluid*; D015153:Blotting, Western / Q000662:veterinary; D004679:Encephalomyelitis / Q000134:cerebrospinal fluid / Q000175:diagnosis / Q000662:veterinary*; D004906:Erythrocyte Count / Q000662:veterinary; D005189:False Positive Reactions; D006734:Horse Diseases / Q000134:cerebrospinal fluid / Q000175:diagnosis*; D006736:Horses; D007074:Immunoglobulin G / Q000097:blood / Q000134:cerebrospinal fluid; D011446:Prospective Studies; D012522:Sarcocystis / Q000276:immunology*; D012523:Sarcocystosis / Q000134:cerebrospinal fluid / Q000175:diagnosis / Q000662:veterinary*; D013048:Specimen Handling / Q000592:standards / Q000662:veterinary
D000418:Albumins; D000913:Antibodies, Protozoan; D007074:Immunoglobulin G