Objective—To determine and compare sensitivity, specificity,
accuracy, and predictive values of measurement of
serum total protein concentration by refractometry as
well as 5 commercially available kits for the diagnosis of
failure of passive transfer (FPT) of immunity in foals.
Animals—65 foals with various medical problems
and 35 clinically normal foals.
Procedure—IgG concentration in serum was assessed
by use of zinc sulfate turbidity (assay C), glutaraldehyde
coagulation (assay D), 2 semiquantitative immunoassays
(assays F and G), and a quantitative immunoassay
(assay H). Serum total protein concentration was
assessed by refractometry. Radial immunodiffusion
(assays A and B) was used as the reference method.
Results—For detection of IgG < 400 mg/dL, sensitivity
of assay H (100%) was not significantly different from
that of assays C, E, and G (88.9%). Specificity of assays
H (96.0%) and G (95.8%) was significantly higher than
that of assays C (79.4%) and E (78.1%). For detection
of IgG < 800 mg/dL, sensitivities of assays H (97.6%), D
(92.9%), C (81.0%), and G (81.0%) were significantly
higher than that of assay F (52.4%). Specificity of
assays F (100%), G (94.7%), and H (82.8%) was significantly
higher than that of assays C (56.9%) and D
(58.6%). Serum total protein concentration ≤ 4.5 g/dL
was suggestive of FPT, whereas values ≥ 6.0 g/dL indicated
adequate IgG concentrations.
Conclusions and Clinical Relevance—Most assays
were adequate as initial screening tests. However,
their use as a definitive test would result in unnecessary
treatment of foals with adequate IgG concentrations.
(J Am Vet Med Assoc 2005;227:1640–1645)