Methodological problems in the measurement of interleukin-33 concentrations in patients with heart failure with a reduced ejection fraction

We have read manuscript entitled “The concentration of interleukin-33 (IL-33) in heart failure with reduced ejection fraction. Anatol J Cardiol 2019; 21: 305-13” with great interest (1). The study included 155 patients with heart failure and 60 healthy individuals to compare IL-33 levels (1). The authors pointed out that blood samples collected from patients on admission were stored at −80 °C until further use; however, they did not mention about blood sample storage time comparison between the patient and the control group. Storage time for blood samples may affect IL33 concentration measurement and change results; for example, variable cytokine concentration levels were seen with different blood storage durations in the previous study (2).