PLATELET-LYMPHOCYTE RATIO AS A NOVEL SURROGATE MARKER TO DIFFERENTIATE THYROTOXIC PATIENTS WITH GRAVES DISEASE FROM SUBACUTE THYROIDITIS: A CROSS-SECTIONAL STUDY FROM SOUTH INDIA

Objective: Graves disease (GD) and the toxic phase of subacute thyroiditis (SAT) have similar clinical and biochemical presentations, and differentiating them requires sophisticated investigations. Since thyroid hormones have been noted to affect all hematologic cell lines, we have used the platelet lymphocyte ratio (PLR)-an index usually utilized in inflammatory or malignant disorders-to compare patients with and without thyrotoxicosis and to analyze its use in distinguishing between patients with GD and SAT prior to therapy. Methods: This was a cross-sectional study conducted in the Department of Endocrinology, Christian Medical College, Vellore, India. During the study period, 800 patients with features of thyrotoxicosis visited the outpatient clinic. Those who had thyroid radioiodine (I-131) uptake (RAIU) study and complete blood count (CBC) at diagnosis were included (N = 500). Based on the RAIU values, these were divided as GD (n = 354) and SAT (n = 146). Baseline characteristics, thyroid function tests, and components of the CBC and PLR were obtained. The data were compared with a group of 250 matched euthyroid controls. Analyses were performed using SPSS version 21.0 software. Results: PLR showed significant reductions in both GD and SAT patients when compared to euthyroid controls (P =.01), with greater reductions seen in GD than SAT (74.5 +/- 19 vs. 84.4 +/- 26; P =.01). Using receiver operating characteristic analysis of PLR, an optimal PLR cut-off of 70.4 was found to differentiate GD from SAT with a sensitivity of 86% and specificity of 74%. Conclusion: PLR can be used as a novel surrogate marker to differentiate between patients with GD and SAT prior to therapy, especially in resource-limited settings.