Ann Lab Med 2019; 39(4): 345-357  https://doi.org/10.3343/alm.2019.39.4.345
The Platelet-to-Lymphocyte Ratio as an Inflammatory Marker in Rheumatic Diseases
Armen Yuri Gasparyan , M.D., Ph.D.1, Lilit Ayvazyan , Ph.D.2, Ulzhan Mukanova , M.D., Ph.D.3, Marlen Yessirkepov , M.D., Ph.D.4, and George D. Kitas , M.D., Ph.D., F.R.C.P.1,5
1Departments of Rheumatology and Research and Development, Dudley Group NHS Foundation Trust (Teaching Trust of the University of Birmingham, UK), Russells Hall Hospital, Dudley, West Midlands, UK; 2Department of Medical Chemistry, Yerevan State Medical University, Yerevan, Armenia; 3Department of Surgical Disciplines, South Kazakhstan Medical Academy, Shymkent, Kazakhstan; 4Department of Biology and Biochemistry, South Kazakhstan Medical Academy, Shymkent, Kazakhstan; 5Arthritis Research UK Epidemiology Unit, University of Manchester, Manchester, UK
Corresponding author: Armen Yuri Gasparyan, M.D., Ph.D. https://orcid.org/0000-0001-8749-6018
Departments of Rheumatology and Research and Development, Dudley Group NHS Foundation Trust (Teaching Trust of the University of Birmingham, UK) Russells Hall Hospital, Pensnett Road, Dudley DY1 2HQ, West Midlands, UK
Tel: +44-(0)-1384-456111, Fax: +44-(0)-1384-244272
E-mail: a.gasparyan@gmail.com
Received: November 14, 2018; Revised: December 12, 2018; Accepted: February 7, 2019; Published online: July 1, 2019.
© Korean Society for Laboratory Medicine. All rights reserved.

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.
Abstract
The platelet-to-lymphocyte ratio (PLR) has emerged as an informative marker revealing shifts in platelet and lymphocyte counts due to acute inflammatory and prothrombotic states. PLR has been extensively examined in neoplastic diseases accompanied by immune suppression and thrombosis, which can be predicted by combined blood cell counts and their ratios. Several large observational studies have demonstrated the value of shifts in PLR in evaluating the severity of systemic inflammation and predicting infections and other comorbidities, in inflammatory rheumatic diseases. The value of PLR as an inflammatory marker increases when its fluctuations are interpreted along with other complementary hematologic indices, particularly the neutrophil-to-lymphocyte ratio (NLR), which provides additional information about the disease activity, presence of neutrophilic inflammation, infectious complications, and severe organ damage in systemic lupus erythematosus. PLR and NLR have high predictive value in rheumatic diseases with predominantly neutrophilic inflammation (e.g., Behçet disease and familial Mediterranean fever). High PLR, along with elevated platelet count, is potentially useful in diagnosing some systemic vasculitides, particularly giant-cell arteritis. A few longitudinal studies on rheumatic diseases have demonstrated a decrease in PLR in response to anti-inflammatory therapies. The main limitations of PLR studies are preanalytical faults, inadequate standardization of laboratory measurements, and inappropriate subject selection. Nonetheless, accumulating evidence suggests that PLR can provide valuable information to clinicians who encounter multisystem manifestations of rheumatic diseases, which are reflected in shifts in platelet, lymphocyte, neutrophil, or monocyte counts. Interpretation of PLR combined with complementary hematologic indices is advisable to more accurately diagnose inflammatory rheumatic diseases and predict related comorbidities.
Keywords: Platelet count, Lymphocyte count, Neutrophil count, Inflammation, Rheumatic diseases, Markers, Platelet-to-lymphocyte ratio



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