Seasonal Variation in Autoimmune Hemolytic Anemia: A National Database Analysis
Authors: Guntupalli Srinandan , Patel Dhara , Soni Ronak Gajendra kumar , Devarashetty Sindhupriya , Mansour Richard Preston 
Published: October 2019

Abstract
Background:
Autoimmune hemolytic anemia (AIHA) is a decompensated acquired hemolysis caused by host's immune system acting against its own red cell antigens. Serologically, it can be divided to warm hemolytic anemia, cold hemolytic anemia, paroxysmal cold hemoglobinuria and mixed AIHA. Pathogenesis of AIHA comprises of a series of complex interactions between genetics, environmental either conferring to protective or deteriorating effects. Among these, climatic changes appears to be key as it involves many triggers such as viral infections, temperature and other host factors. We reviewed a large national hospitalization database to determine whether rates of autoimmune hemolytic anemia have a seasonal variation over the past decade.
Methods:
We examined the Nationwide Inpatient Sample (NIS), a nationally representative survey of hospitalizations conducted by the Healthcare Cost and Utilization Project in collaboration with participating states. It is the largest all-payer inpatient dataset in the United States and includes a 20% sample of United States community hospitals that approximates 20% of all US community hospitals. The Nationwide Inpatient Sample (NIS) database was used to estimate annual number of hospitalizations from 2000 - 2012. Identification of autoimmune hemolytic anemia related hospitalizations was based on the designation of the prior validated International Classification of Diseases (9th Edition) Clinical Modification (ICD-9-CM) diagnosis code 283 as the principal discharge diagnosis. The frequency of hospitalization per month cumulative over 13 years was calculated and divided by number of days in that month to determine the mean hospitalizations per day for each month. All calculations were carried out using the weighted estimates approximating nationwide population estimates.
Results:
An estimated 48,416 hospitalizations with primary diagnosis of autoimmune hemolytic anemia occurred in the US from 2000 to 2012 as per NIS database. More specifically, the mean number of hospitalizations per day in each month is shown in Fig. 1. The mean number of hospitalizations each day was highest in November (141 per day) and thereafter the hospitalization rate dropped to a nadir in May (122 per day). There was a significant rising trend of admissions from June towards winter months with peaks in November as depicted in the Fig.1. In general, the number of hospitalization was maximum in the winter months and minimum in summer months as demonstrated in Fig.2.
Conclusion:
We identified for the first time in United States an impressive pattern of seasonal variation in hospitalizations for autoimmune hemolytic anemia with a notable increase in winter and fall and a significant drop during summer months. The seasonal pattern may reflect viral or other triggers for immune system activation. Further efforts need to be made to identify triggers and methods to determine the relationship of these variations and reduce this predictive burden on the overall health care system.
Figure. Figure.

Disclosures
No relevant conflicts of interest to declare.