Background: Cold urticaria (ColdU) is a common type of chronic inducible urticaria. Patients with typical ColdU develop wheals in response to standard cold stimulation tests (CSTs), an ice cube (ICT) or TempTest ®. As of now, the evaluation of CST response is visual and subjective. Validated, robust, and objective test readouts lacking today are needed. Methods: We subjected 63 patients (39 with typical ColdU and 24 with atypical ColdU) and 15 healthy controls (HCs) to TempTest ® CSTs and critical temperature threshold assessments. Blood microcirculation photoplethysmography (PPG) measurements were performed 5 min before and 10 min after the ICT on the volar forearm. Results: PPG amplitudes reflected normal baseline skin blood perfusion in patients with typical or atypical ColdU. Ice cube CSTs induced a marked increase in blood perfusion and PPG amplitudes in typical but not atypical ColdU, with distinct pre-post CST changes in PPG amplitudes in the former. The ratio of post-provocation and baseline PPG amplitudes ( R PPG) in typical ColdU patients exceeded that in atypical ColdU patients and HCs more than 3-fold. Almost all typical ColdU patients (98%), but only 13% of atypical ColdU patients and 7% of HCs had R PPG >3. PPG results matched those of CSTs in 94% of all tested individuals. Conclusion: Photoplethysmographic assessments of CST responses appear accurate and provide objective readouts. PPG may be of use in diagnosing ColdU, distinguishing typical and atypical ColdU, and more precise threshold testing.

Background: The global epidemiology of asthma among COVID-19 patients presents striking geographic differences defining high and low [asthma and COVID-19] co-occurrence prevalence zones (1). The objective of the present study was to compare asthma prevalence among hospitalized COVID-19 patients in major global hubs across the world with the application of common inclusion criteria and definitions. Methods: We built a network of six academic hospitals in Stanford (Stanford University)/USA, Frankfurt (Goethe University), Giessen (Justus Liebig University) and Marburg (Philipps University)/Germany, and Moscow (Clinical Hospital 52 in collaboration with Sechenov University)/Russia. We collected clinical and laboratory data for patients hospitalized due to COVID-19. Comorbidities reported were based on the 2020 International Classification of Diseases-10th Revision codes. Results: Asthmatics were overrepresented among hospitalized COVID-19 patients in Stanford and underrepresented in Moscow and Germany as compared to the prevalence among adults in the local community. Asthma prevalence was similar among ICU and hospital non-ICU patients, which implied that the risk for developing severe COVID-19 was not higher among asthmatics. The number of males and comorbidities was higher among COVID-19 patients in the Stanford cohort, and the most frequent comorbidities among these asthma patients were other chronic inflammatory airway disorders such as chronic obstructive pulmonary disease (COPD). Conclusion: Observed disparity in COVID-19-associated risk among asthmatics across countries and continents is connected to varying prevalence of underlying comorbidities, particularly COPD. Public health policies in the future will need to consider comorbidities with an emphasis on COPD for prioritization of vaccination and preemptive treatment.