Retrospective assessment of seasonal allergic symptoms: over-rating but useful

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Abstract
Background The history of the severity of seasonal allergic symptoms is often obtained post‐seasonally as a retrospective assessment. Correct rating is essential when determining the efficacy of pharmaceutical treatment, indications for allergen‐specific immunotherapy (SIT), or inclusion into controlled clinical studies. Objectives To investigate the agreement between in‐ and post‐seasonal ratings of seasonal symptoms, and to investigate whether the effect of SIT could be detected retrospectively. Material and methods Thirty‐five birch pollen‐allergic patients were allocated to SIT or placebo in a double‐blind study. Assessment of severity of symptoms from the nose, eyes and lungs were performed daily during the season 2000, and post‐seasonally 6 months after the season in 1999 and 2000. A four‐point verbal descriptor scale (VDS‐4) was used at all occasions. A mean in‐seasonal symptom rating was calculated for four periods: the day, the week and the 2 weeks with the highest symptoms score, and the arithmetic season (the period covering the mid‐90% of the accumulated pollen count). In‐ and post‐seasonal ratings were compared with Cohen's weighted kappa (κw). Results Agreement between in‐seasonal and retrospective ratings was fair to moderate (κw: 0.30–0.60). Post‐seasonal ratings were most related to symptoms experienced in the week with the highest symptom scores, and least related to the arithmetic season. The post‐seasonal ratings were significantly skewed towards higher symptom scores than the mean of in‐seasonal ratings in periods ≥ 2 weeks. Despite being comparable before intervention, only in the SIT‐treated group was a significant decrease in post‐season ratings of severity of rhinoconjunctivitis apparent (P < 0.05). Asthma scores were not reduced but fewer patients in the SIT group reported lung symptoms (P < 0.001). Conclusion Post‐seasonal assessment of seasonal allergic symptoms generally describes a shorter period than the arithmetic season. Post‐season assessment tends to over‐rate average symptom severity, but appears sufficiently sensitive to detect treatment efficacy.