Evaluation of the Diagnostic Accuracy of Serum Albumin and Globulin in Pyogenic Spondylitis

<b>Background:</b> Serum markers are commonly used to diagnose bone and joint infections; however, their accuracy for diagnosing pyogenic spondylitis remains unproven. This study aimed to validate the diagnostic accuracy of inflammatory, nutritional, and immunological serum markers for spinal infections and identify the most effective combinations. <b>Methods:</b> The retrospective cohort study analyzed 656 patients who visited the hospital for spinal diseases between 1 January 2004 and 31 March 2021; a total of 76 were diagnosed with pyogenic spondylitis. Blood samples were analyzed for serum albumin (Alb), total protein (TP), globulin (Glb), C-reactive protein (CRP), platelet count, white blood cell count, neutrophil count, lymphocyte count, and monocyte count. Combination markers, including albumin-globulin ratio (AGR), CRP-albumin ratio (CAR), CRP-AGR (CAGR), neutrophil-lymphocyte ratio (NLR), and platelet-lymphocyte ratio (PLR), were also evaluated. Receiver operating characteristic curves were used to determine each marker's diagnostic performance. Furthermore, multivariate analysis was performed to examine the odds ratios. <b>Results:</b> Patients with pyogenic spondylitis showed significantly different levels in Alb (<i>p</i> < 0.0001), Glb (<i>p</i> < 0.0001), CRP (<i>p</i> < 0.0001), platelet count (<i>p</i> < 0.0001), WBC count (<i>p</i> < 0.0006), neutrophil count (<i>p</i> = 0.0019), lymphocyte count (<i>p</i> = 0.0085), AGR (<i>p</i> < 0.0001), CAR (<i>p</i> < 0.0001), CAGR (<i>p</i> < 0.0001), NLR (<i>p</i> < 0.0001), and PLR (<i>p</i> < 0.0001). CRP (AUC = 0.80) showed good diagnostic accuracy, while combination markers CAR (AUC = 0.82) and CAGR (AUC = 0.83) had the highest areas under the curve (AUC). Multivariate analysis indicated that decreased age and the presence of comorbidities (including chronic kidney disease, chronic liver disease, malignancy, or diabetes), were independent predictors of early pyogenic spondylitis (OR_age = 0.93, OR_comorbidities = 16.98, p_age = 0.0005, and p_comorbidities = 0.0001). In patients with low-inflammatory pyogenic spondylitis, significant differences were observed in TP (<i>p</i> = 0.0293), Glb (<i>p</i> = 0.0012), CRP (<i>p</i> = 0.0023), platelet count (<i>p</i> = 0.0108), AGR (<i>p</i> = 0.0044), CAR (<i>p</i> = 0.0006), CAGR (<i>p</i> = 0.0004), PLR (<i>p</i> = 0.0192), and NLR (<i>p</i> = 0.0027), with CAGR showing the highest AUC (AUC = 0.70) among them. <b>Conclusions:</b> Serum combination markers (AGR, CAGR, CAR, PLR, and NLR) showed diagnostic value for pyogenic spondylitis, with CAGR achieving the highest accuracy. In low-inflammatory pyogenic spondylitis patients (CRP ≤ 1.0 mg/dL), these markers may aid diagnosis.