Immunoglobulin Free Light Chains as a Biomarker of Inflammation and Heart Failure in Myocarditis and Non-Inflammatory Heart Disease

<b>Aim</b>: to study the level of immunoglobulin FLC in patients with myocarditis in comparison with non-inflammatory heart diseases, and FLC's correlation with the severity of CHF. <b>Methods</b>: Ninety-nine patients (41 women, 59.6 ± 14.6 y.o.) were included in the study: 50 patients with myocarditis [confirmed by myocardial biopsy (n = 20) and/or cardiac MRI]; 49 patients with non-inflammatory heart disease. CHF was diagnosed in 66% and 65% of patients, respectively. The levels of FLC were determined using the 'Cloneus S-FLC-K TIA Kit' and 'Cloneus S-FLC-L TIA Kit' reagents. <b>Results</b>: Elevated FLC levels were found in 56% of patients with myocarditis and in 67% of comparison group patients (<i>p</i> > 0.05). Mean FLC kappa levels were 13.4 [11.7; 16.7] and 16.0 [11.3; 23.7] mg/L, FLC lambda 22.7 [16.7; 32.4] and 24.7 [18.1; 39.1] mg/L, FLC kappa/lambda ratio 0.62 [0.50; 0.73] and 0.65 [0.56; 0.76] in myocarditis and comparison groups, respectively; there were no significant differences between groups. Both groups showed correlations of FLC levels with levels of CRP and leukocytes, as well as with glomerular filtration rate, CHF NYHA class, and left ventricular ejection fraction. Only in patients with myocarditis did we observe a significant correlation between both kappa and lambda FLC and NT-proBNP (r = 0.528, <i>p</i> = 0.004, and r = 0.756, <i>p</i> < 0.001) and high-sensitivity troponin (r = 0.829, <i>p</i> = 0.042) levels. <b>Conclusions</b>: Increased FLC level may be considered an important pathogenetic link reflecting both specific mechanisms of myocarditis and severity of CHF. The determination of FLC can be used as an additional diagnostic marker, as well as one predictor of the decompensated course of myocarditis.