Total protein measurement in canine cerebrospinal fluid: agreement between a turbidimetric assay and 2 dye-binding methods and determination of reference intervals using an indirect a posteriori method.
BACKGROUND
In veterinary clinical laboratories, qualitative tests for total protein measurement in canine cerebrospinal fluid (CSF) have been replaced by quantitative methods, which can be divided into dye-binding assays and turbidimetric methods. There is a lack of validation data and reference intervals (RIs) for these assays.


OBJECTIVE
The aim of the present study was to assess agreement between the turbidimetric benzethonium chloride method and 2 dye-binding methods (Pyrogallol Red-Molybdate method [PRM], Coomassie Brilliant Blue [CBB] technique) for measurement of total protein concentration in canine CSF. Furthermore, RIs were determined for all 3 methods using an indirect a posteriori method.


METHODS
For assay comparison, a total of 118 canine CSF specimens were analyzed. For RIs calculation, clinical records of 401 canine patients with normal CSF analysis were studied and classified according to their final diagnosis in pathologic and nonpathologic values.


RESULTS
The turbidimetric assay showed excellent agreement with the PRM assay (mean bias 0.003 g/L [-0.26-0.27]). The CBB method generally showed higher total protein values than the turbidimetric assay and the PRM assay (mean bias -0.14 g/L for turbidimetric and PRM assay). From 90 of 401 canine patients, nonparametric reference intervals (2.5%, 97.5% quantile) were calculated (turbidimetric assay and PRM method: 0.08-0.35 g/L (90% CI: 0.07-0.08/0.33-0.39); CBB method: 0.17-0.55 g/L (90% CI: 0.16-0.18/0.52-0.61). Total protein concentration in canine CSF specimens remained stable for up to 6 months of storage at -80°C.


CONCLUSIONS
Due to variations among methods, RIs for total protein concentration in canine CSF have to be calculated for each method. The a posteriori method of RIs calculation described here should encourage other veterinary laboratories to establish RIs that are laboratory-specific.
Clinical Laboratory, Vetsuisse Faculty, University of Zurich, Zurich, Switzerland.
B
B
Riond
F
F
Steffen
O
O
Schmied
R
R
Hofmann-Lehmann
H
H
Lutz
D000818:Animals; D002556:Cerebrospinal Fluid Proteins / Q000032:analysis*; D004285:Dogs / Q000134:cerebrospinal fluid*; D005260:Female; D007202:Indicators and Reagents; D008297:Male; D008982:Molybdenum; D009391:Nephelometry and Turbidimetry / Q000662:veterinary; D011748:Pyrogallol; D011933:Reagent Kits, Diagnostic / Q000662:veterinary; D012016:Reference Values; D012394:Rosaniline Dyes
D002556:Cerebrospinal Fluid Proteins; D007202:Indicators and Reagents; D011933:Reagent Kits, Diagnostic; D012394:Rosaniline Dyes; D011748:Pyrogallol; C044659:molybdate; D008982:Molybdenum; C004692:coomassie Brilliant Blue
A posteriori method; canine cerebrospinal fluid; dye-binding method; reference interval; total protein; turbidimetric method