Rheumatoid arthritis (RA) is a chronic inflammatory autoimmune disease primarily affecting synovial joints, characterized by persistent inflammation, progressive joint destruction, and systemic manifestations that can lead to irreversible deformity and functional disability if inadequately managed. Its pathophysiology involves genetic predisposition, environmental triggers, and immune dysregulation, culminating in synovial hyperplasia, pannus formation, and cartilage and bone erosion (Scherer et al., 2020). RA is a significant global health concern, affecting 0.5–1% of the world's population (Almutairi et al., 2021; Shi et al., 2025), and approximately 0.28–0.75% of the adult Indian population (Malaviya et al., 1993).

Lactate dehydrogenase (LDH), a ubiquitous cytoplasmic enzyme catalyzing the reversible conversion of lactate to pyruvate, has gained attention as a biomarker of RA disease activity, with elevated levels reflecting increased cellular turnover, tissue damage, and metabolic demands of chronic inflammation (Patel et al., 2018). The interplay between these biomarkers underscores the multifaceted nature of RA, offering valuable insights into disease pathophysiology, activity assessment, and treatment monitoring, thereby supporting improved diagnostic and therapeutic strategies.

Despite growing evidence supporting the role of homocysteine and LDH in RA pathophysiology, their combined utility as disease activity markers—particularly in relation to disease duration, joint involvement pattern, and treatment status—remains underexplored in the Indian population. The present study was therefore undertaken to evaluate serum homocysteine and LDH levels in RA patients at a tertiary care centre and assess their association with clinico-demographic variables.

MATERIALS AND METHODS

This was an observational cross-sectional study conducted at the Department of Biochemistry in collaboration with the Department of Medicine, Gandhi Medical College and Hamidia Hospital, Bhopal, over a duration of 18 months. The study included 127 subjects of either sex, diagnosed with Rheumatoid Arthritis within the previous 5 years as per the 2010 ACR/EULAR criteria (Aletaha et al., 2010; Kay & Upchurch, 2012), aged 18 years or above, attending the Medicine OPD. Patients with any other autoimmune disease, other types of arthritis, conditions requiring frequent blood transfusions, or those who were pregnant or lactating were excluded.

The sample size was calculated using the formula n = z²p(1−p)/d², with a 95% confidence level (z = 1.96) and 5% precision. Ethical clearance was obtained from the Institutional Ethics Committee of Gandhi Medical College, and written informed consent was obtained from all participants in their preferred language.

Blood specimens were collected by venepuncture from the antecubital vein, allowed to clot, and serum was separated by centrifugation at 3000 rpm for 15 minutes. All biochemical analyses were performed in the Biochemistry laboratory following NCCLS standards. Serum Lactate Dehydrogenase (LDH) was estimated by the IFCC-recommended kinetic UV method using a Beckman Coulter AU5800 Series analyzer. The method is based on LDH-catalyzed conversion of L-lactate to pyruvate with simultaneous reduction of NAD⁺ to NADH, measured spectrophotometrically at 340 nm; normal reference range: 140–280 U/L. Rheumatoid Factor (RF) was quantified by latex-enhanced immunoturbidimetry on the Beckman Coulter AU5800 analyzer; values ≤14 IU/mL are considered normal.

RESULTS

A total of 127 RA patients were enrolled. The majority were female (60.6%; F:M ratio ~1.5:1), and the predominant age group was 41–60 years (52.8%). Regarding disease duration, 44.1% had early RA (<8 weeks), 36.2% had intermediate duration (8–16 weeks), and 19.7% had longer duration (>16 weeks). Small joint involvement was predominant (87.4%), and most patients (83.5%) were on methotrexate therapy (Table 1).

All 127 patients had serum LDH levels above the normal range (140–280 U/L), with a mean of 447.80 ± 93.71 U/L. The majority (34.6%) showed levels 50–100% above normal (Table 2). Males had significantly higher mean LDH than females (470.40 ± 85.31 vs. 433.12 ± 96.49 U/L; p = 0.028) (Table 4), though categorical distribution by gender was not significant (p = 0.062). Age group differences in LDH were not statistically significant (ANOVA p = 0.250) (Table 3).

Disease duration showed a strong inverse relationship with LDH activity: patients with <8 weeks duration had the highest mean LDH (532.32 ± 67.42 U/L), followed by the 8–16 weeks group (390.43 ± 45.94 U/L) and the >16 weeks group (364.00 ± 37.86 U/L), with highly significant differences (F = 118.806; p <0.001) (Table 5). Small joint involvement was associated with significantly higher LDH (462.79 ± 89.69 U/L) compared to large joint involvement (343.75 ± 39.48 U/L; p <0.001) (Table 6). Patients not on methotrexate had higher mean LDH (485.71 ± 71.38 U/L) than those on treatment (440.28 ± 96.03 U/L; p = 0.042) (Table 7).

Table 1. Demographic and clinical profile (n = 127)

Table 2. Serum LDH elevation categories (n = 127)

Normal range: 140–280 U/L. All 127 patients had LDH above normal. Overall mean ± SD: 447.80 ± 93.71 U/L.

Table 3. Mean serum LDH by age group (ANOVA)

F = 1.346; p = 0.250 (not significant)

Table 4. Mean serum LDH by gender (t-test)

*Statistically significant (p < 0.05)

Table 5. Mean serum LDH by disease duration (ANOVA)

*Statistically significant (p < 0.05). LDH decreases as disease duration increases.

Table 6. Mean serum LDH by joint involvement (t-test)

*Statistically significant (p < 0.05)

Table 7. Mean serum LDH by methotrexate use (t-test)

*Statistically significant (p < 0.05). Categorical chi-square: p = 0.074 (not significant).

DISCUSSION

Rheumatoid arthritis (RA) is a chronic systemic autoimmune inflammatory disease primarily affecting synovial joints, leading to progressive joint destruction, disability, and premature mortality if untreated. As a multisystem disorder, RA also involves cardiovascular, pulmonary, and ocular systems (Chauhan et al., 2023; Smolen et al., 2018). This study evaluated serum levels of lactate dehydrogenase (LDH) and homocysteine as biochemical biomarkers in RA patients, examining their clinical significance in relation to disease activity, demographic variables, disease duration, joint involvement pattern, and methotrexate (MTX) usage.

4.1 Age and Gender Distribution

Among 127 enrolled RA patients, the majority (70.9%) were middle-aged (31–60 years), with the largest group in the 41–50 years range (27.6%). This is consistent with Indian epidemiological studies (Misra et al., 2024), though contrasting with global data reporting peak incidence at 65–69 years (Black et al., 2023). The discrepancy likely reflects India's younger demographic profile, earlier disease onset due to genetic and environmental factors, and tertiary care referral patterns.

Female patients predominated (60.6%; F:M ratio ≈1.5:1), consistent with RA's well-established female predisposition (global F:M ratio 2.45:1) (Black et al., 2023). The moderately lower ratio observed may reflect regional genetic influences, differential healthcare-seeking behaviour, or hormonal variation. Female predominance and middle-aged peak are attributed to autoimmune mechanisms, estrogen fluctuations during perimenopause/menopause affecting immune regulation, and MTHFR C677T polymorphism influencing inflammatory pathways (Chaabane et al., 2018; Chauhan et al., 2023).

4.2 Disease Duration and Joint Involvement

Most patients had early RA (<8 weeks: 44.1%; 8–16 weeks: 36.2%), with 80.3% having disease duration ≤16 weeks. Small joint involvement was predominant (87.4%), reflecting the classic symmetric polyarthritis of RA involving MCP, PIP, and MTP joints (Malaviya et al., 1993). These findings reflect the impact of the 2010 ACR/EULAR classification criteria (Aletaha et al., 2010), which emphasise early disease features, enabling timely intervention within the critical therapeutic window to prevent irreversible joint damage.

4.3 Methotrexate Usage

Methotrexate was being used by 83.5% of patients, consistent with current evidence-based guidelines positioning MTX as the anchor conventional synthetic DMARD in RA management owing to its favourable efficacy, safety, and cost-effectiveness (Smolen et al., 2023). This high adoption rate confirms appropriate standard-of-care implementation in the present cohort.

4.4 Serum Lactate Dehydrogenase (LDH) Activity

All 127 RA patients had elevated serum LDH above the normal reference range (140–280 U/L), with a mean of 447.80 ± 93.71 U/L. Yang et al. (2024) identified key genes in LDH-related lactate metabolism regulating macrophage function in RA. Souto-Carneiro et al. (2020) demonstrated 2.6–3.7-fold higher lactate production in RA CD8+ T cells, with overexpression of LDHA across all subsets. These findings indicate metabolic reprogramming toward aerobic glycolysis (Warburg effect) as a driver of systemic LDH elevation in RA (Gupta, 2022). Conversely, Patel et al. (2018) found no proportional rise in serum LDH relative to disease severity (CDAI and DAS28-CRP), suggesting limitations of total serum LDH as a standalone severity marker.

The pathophysiological basis includes: (i) metabolic reprogramming of immune cells (synovial fibroblasts, T cells, B cells, macrophages) toward aerobic glycolysis with increased lactate and LDH release; (ii) pro-inflammatory cytokines (TNF-α, IL-1β) increasing cellular membrane permeability promoting LDH leakage; and (iii) chronic synovial inflammation perpetuating cellular activation, proliferation, and apoptosis with ongoing LDH release (Souto-Carneiro et al., 2020; Gupta, 2022).

4.5 Age and Gender Variations in LDH

Mean serum LDH was highest in the 21–30 age group (498.33 ± 78.95 U/L), possibly reflecting more aggressive early-onset disease, and lowest in the ≤20 age group (394.00 ± 75.03 U/L). However, ANOVA showed no statistically significant difference across age groups (F = 1.346, p = 0.250), indicating LDH elevation is a consistent feature of RA irrespective of age. Males had significantly higher mean LDH (470.40 ± 85.31 U/L) compared to females (433.12 ± 96.49 U/L) (t = −2.225, p = 0.028). This may be attributed to higher baseline muscle mass and differing muscle fibre composition in males, alongside gender-specific hormonal influences on inflammatory cell activation (Gupta, 2022).

STRENGTHS AND LIMITATIONS

The universal elevation of serum LDH across all 127 patients, with statistically significant associations with gender (p = 0.028), disease duration (p <0.001), joint involvement (p <0.001), and methotrexate usage (p = 0.042), supports its utility as a consistent inflammatory marker in RA. However, LDH lacks diagnostic specificity, being elevated in hemolysis, hepatic disease, malignancy, and myocardial injury. LDH isoenzyme profiling was not performed, limiting mechanistic interpretation. LDH levels were not correlated with validated disease activity scores such as DAS28 or CDAI, and the cross-sectional design precludes causal inference.

CONCLUSION

Serum lactate dehydrogenase (LDH) emerged as a consistently elevated and clinically significant biomarker in patients with rheumatoid arthritis, reflecting the underlying metabolic and inflammatory burden of the disease. The highest LDH levels were observed in patients with early-stage disease, small joint involvement, and those not receiving adequate disease-modifying therapy, indicating a strong association between LDH elevation and active inflammatory processes. The significantly greater elevation noted in male patients further suggests the influence of biological and hormonal factors on inflammatory cellular injury.

These findings support the incorporation of serum LDH into routine biochemical assessment as a simple, responsive, and cost-effective indicator for evaluating disease activity, monitoring therapeutic response, and identifying patients with high inflammatory burden, particularly during the early and clinically active stages of rheumatoid arthritis. Future studies should incorporate LDH isoenzyme profiling, correlation with validated disease activity scores, and longitudinal follow-up to further delineate its prognostic utility.

ACKNOWLEDGEMENTS
We sincerely thank the Departments of Biochemistry and Medicine, Gandhi Medical College, Bhopal, for their guidance and support throughout this study, including cooperation in patient recruitment. We are grateful to the Central Clinical Laboratory, Hamidia Hospital, for biochemical analysis, the Institutional Ethics Committee, GMC Bhopal, for ethical approval, and the Department of Preventive and Social Medicine, GMC Bhopal, for statistical support. No external funding was received for this research.

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