Research Journal of Biological Sciences
ISSN: Online 1993-6087ISSN: Print 1815-8846
Abstract
Conventional binary (positive/negative) diagnostic thresholds in serological surveillance frequently overlook sub-threshold antibody reactivity, creating analytical blind spots. This retrospective study evaluated the relationship among serum agglutination test (SAT) antibody titers, visual reaction intensity grades (+1 to +4), and paired serum–milk direct enzyme-linked immunosorbent assay (I-ELISA) outcomes, utilizing archived laboratory records from 270 unvaccinated cattle investigated following abortion or clinical suspicion of brucellosis in Türkiye. Following the exclusion of ambiguous agglutination records (n = 4) and an indeterminate milk ELISA result (n = 1), 266 animals were available for titer stratification and 269 for paired matrix evaluation. Markedly high immunoassay reactivity was detected below the conventional 1:40 diagnostic cutoff: among 102 SAT-negative cattle, I-ELISA positivity was identified in 41.2% (42/102) of serum and 64.7% (66/102) of milk samples. Within the low-titer stratum (1:10–1:20), positivity reached 66.1% (37/56) in serum and 78.6% (44/56) in milk. Reaction grades within low titers demonstrated no monotonic correlation with IgG-specific ELISA positivity, reflecting functional divergence between pentameric IgM-driven lattice formation and monomeric IgG affinity. Paired matrix evaluation revealed significant directional asymmetry: 42 cattle were milk-positive yet serum-negative, compared with only six displaying the reciprocal profile (exact McNemar p = 1.01 × 10 ; observed agreement 82.2% [95% CI: 77.1–86.3%]; Cohen’s kappa κ = 0.534 [95% CI: 0.424–0.644]). Lowering the descriptive SAT threshold from ≥ 1:40 to ≥ 1:10 reclassified 37 immunoassay-reactive cases, moderately increasing crude agreement from 68.8% to 75.6% (95% CI: 70.1–80.3%) and chance-adjusted concordance (κ = 0.417 to κ = 0.464 [95% CI: 0.354–0.574]); however, it concomitantly increased SAT-positive/ELISA-negative discordance from 4 to 23 animals (1.5% to 8.6%). In the absence of definitive bacteriological isolation, asymmetric milk reactivity warrants cautious interpretation, representing either localized intramammary immunoglobulin secretion or analytical matrix interference. These findings suggest that reporting discrete titration endpoints alongside reaction grades and paired matrix screening may provide a valuable methodological framework for refining bovine brucellosis surveillance and control protocols.
How to cite this article:
Ufuk Ülker. Diagnostic Threshold Vulner ability and Matrix Discordance in Bovine Brucellosis Serology: An Advanced Evaluation of Granular Dilution End points and Reaction Grades.
DOI: https://doi.org/10.36478/10.36478/makrjbs.2026.8.15
URL: https://www.makhillpublications.co/view-article/1815-8846/10.36478/makrjbs.2026.8.15