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REVIEW ARTICLESerum IgG4 Concentration in IgG4-Related Disease by Shigeyuki Kawa, Markus Skold, David B. Ramsden, Antony Parker, Stephen J. Harding

Background: IgG4-related disease (IgG4-RD) is an immune-mediated and chronic fibroinflammatory condition that affects almost any organ and often involves multiple organs in the same patient. In this review article, we address the clinical utility of measuring serum immunoglobulin G subclass 4 concentration ([IgG4]) in IgG4-RD diagnosis and in disease monitoring.
Methods: We discuss the latest literature on the relevance of [IgG4] to the investigation and management of IgG4RDs. In addition, we discuss the potential role of serum [IgG4] measurements in other inflammatory conditions and cancers.
Results: Increasing awareness of IgG4-RD among clinicians has led to a growing list of organ systems that can be affected by this chronic condition and the development of new organ-specific diagnostic guidelines. Diagnosis of IgG4-RD depends on multiple clinical and laboratory tests, including serology. Quantification of serum [IgG4] is included in all IgG4-RD diagnostic guidelines available to-date. The scientific literature supports the idea that elevated serum [IgG4], typically > 135 mg/dL, identifies patients with a more active form of the disease, which correlates with increased concentrations of inflammatory serum biomarkers and hypocomplementemia, increased number of organs affected by the disease, and more extensive organ involvement. These patients seem more resistant to treatment and experience a shorter time to disease relapse compared to IgG4-RD patients with normal serum [IgG4] at the time of diagnosis.
Conclusions: Despite better understanding of how to diagnose IgG4-RD, monitoring for accurate prediction of disease relapse, which may involve organs not affected at the time of presentation, is poorly understood. Timely diagnosis and early detection of disease relapse is important to avoid delayed treatment and potential organ damage.

DOI: 10.7754/Clin.Lab.2017.170403