Development of the immune status questionnaire (ISQ)

Background: The self-assessment of perceived immune status is important, as this subjective observation is leading for individuals to decide whether or not to seek medical help or adapt their lifestyle. Current assessments of perceived immune status are conducted with 1-item ratings [1]. the Immune Function Questionnaire (IFQ) [2], or various self-composed questionnaires. While a 1-item perceived immune functioning score provides no information about which aspects of immune status may be affected, the disadvantage of multiple item scales is that they are time-consuming to complete. This may be a burden to certain patient populations, and limit their use in clinical practice in which quick and cost-effective assessments are sometimes essential. Aim: The aim of the current studies was to develop a short Immune Status Questionnaire (ISQ). Methods: To develop the ISQ, four studies were conducted. Participants were young adults, aged 18 to 30 years old. In Study 1 (n = 295), an adjusted version of the IFQ was administered, which was complemented with the items shortness of breath, skin problems, muscle and joint pain, and the common cold. A stepwise linear regression analysis was conducted to identify those items that had a predictive validity of at least 85% with regard to the sum score of all items. These items were combined to form the ISQ. In Study 2 (n = 569), the ISQ was compared with the 1-item perceived immune functioning score (Donners et al. 2015). In Study 3 (n = 291), the original item scoring was compared to a new Likert scale scoring. Study 4 (n = 52) was conducted to investigate the test-retest reliability of the ISQ. Results: Analysis of the data from Study 1 revealed seven items that together comprised the ISQ (predictive validity of 85%): common cold, diarrhea, sudden high fever, headache, muscle and joint pain, skin problems and coughing. The items are scored on a 5-point Likert scale ranging from 0 to 4. The overall ISQ score ranges from 0 to 28, with higher scores indicating a poorer immune status. Study 2 revealed that the ISQ correlated significantly with the 1-item perceived immune functioning (r = 0.383, p