Chronic diseases rarely affect a single organ system, and routine blood tests often capture this multisystem burden. This narrative review examines how hematological indices (hemoglobin, red and white cell counts, and derived ratios such as the neutrophil-to-lymphocyte ratio, NLR) relate to biochemical markers (creatinine, glomerular filtration rate, calcium, bicarbonate, and C-reactive protein) in chronic disease, using chronic kidney disease (CKD) as the principal model. Literature from 2023 to 2026 was identified through targeted searches of open-access sources and supplemented with key earlier syntheses. Across studies, declining renal function tracked with lower hemoglobin and red cell counts, lower calcium and bicarbonate, and higher creatinine and inflammatory markers, although associations ranged from very strong (creatinine) to weak (calcium, C-reactive protein). NLR showed a consistent but modest association with mortality in hemodialysis and chronic obstructive pulmonary disease. Interpretation is limited by marked heterogeneity, varying cut-offs, small single-centre samples, and probable publication bias. The evidence supports reading hematological and biochemical results together, while cautioning that correlation does not establish causation or justify new thresholds without standardized validation. Multicentre longitudinal studies are needed.