Table 3A.

Summary of studies and their associations

No	Author (year)	Study design	Types of allergy	Purpose	Sample size and group comparison	Subjects characteristics	Association with ABO blood groups
1	Falsarella et al 25 Country: Brazil Year: 2011	Case control	Allergic rhinitis	To determine if ABO phenotypes are associated with allergic rhinitis.	168 patients and 168 controls	Age: 18–85 years, patients matched by age and gender with controls	The O phenotype was associated with susceptibility to allergic rhinitis for men but not for women (p=0.016; OR= 1.735; 95% CI 1.127 to 2.673).
2	Hamad26 Country: Iraq Year: 2016	Cross sectional	Allergic rhinitis	To determine the prevalence of ABO blood groups and to investigate their association with allergic rhinitis and relate this association with genetics.	109	Age: 18–60 years (female and male)	Group O is the most common and has a high level of risk for developing allergic rhinitis (p=0.049).
3	Topno et al 27 Country: India Year: 2017	Case control	Allergic rhinitis	To study the correlation of ABO phenotypes in patients with allergic rhinitis.	100 patients and 100 controls	Outpatient department Ear, Nose and Throat (ENT) Age: 11–70 years, patients matched by age and gender with controls	The O blood group phenotype is associated with allergic rhinitis (OR 3.63, p=0.006).
4	Kauffmann et al 19 Country: France Year: 1996	Cross sectional	Asthma	To assess the role of all three systems—Lewis, secretor and ABO—in lung function, wheezing and asthma.	228 males	Age: 34–50 years, coal miners	Non-secretor subjects of blood group O have significantly lower lung function and higher prevalence of wheezing and asthma (p<0.01).
5	Ronchetti et al 20 Country: Italy Year: 2001	Case control	Asthma	To analyse the joint phenotype ABO/secretor in a cohort of asthmatic children in an attempt to confirm the association observed in adult subjects.	165 children (109 males and 56 females) 362 newborn infants as controls	Outpatients of a paediatric pulmonary clinic or patients who were admitted to a ward of the same clinic for acute respiratory episodes. Age: 1 month–15 years	O/non-secretor in asthmatic male children was higher than the controls (p<0.025).
6	Chen et al 28 Country: Taiwan Year: 2005	Case control	Asthma	To analyse the histo-blood groups of ABO, Lewis and secretor in a cohort of asthmatic children in Taiwan.	136 asthmatic children and 161 aged-matched controls	Age: 6–13 years	Blood group O/secretors were associated with childhood asthma (OR=2.7, 95% CI 1.126 to 6.033, p<0.02)
7	Saini and Yadav29 Country: India Year: 2014	Case control	Asthma	To investigate the association of ABO and Rh (D) allele frequency in patients with asthma.	180 subjects (120 asthmatics and 60 controls)	Patients matched by age, sex and socioeconomic status with controls	A possible association between blood group O and asthma prevalence was noted (p<0.05).
8	Yaro et al 30 Country: Nigeria Year: 2015	Case control	Asthma	To explore the relationship of blood group type and susceptibility to asthma in Sokoto Metropolis, Nigeria.	200 asthmatic patients and 100 adults (control group)	Individuals attending the Pulmonary Unit of Usmanu Danfodiyo University Teaching Hospital, Specialist Hospital and Maryam Abacha Women and Children Hospital, all in Sokoto metropolis, Nigeria	A possible association between blood group A and asthma susceptibility was noted (p<0.05).
9	Gangopadhyay et al 18 Country: India Year: 2006	Cross sectional	Atopic dermatitis	To evaluate the relationship between atopic dermatitis and the ABO blood group.	30 patients with atopic dermatitis	Patients attending the Dermatology Outpatient Department (OPD) of NRS Medical College, Kolkata, over a period of 1 year Age: 6 month–65 years	Blood group O with atopic dermatitis among patients is less prevalent than among controls (p<0.05). Blood group B is the most prevalent in patients with atopic dermatitis, followed by blood group A.
10	Abid33 Country: Pakistan Year: 2015	Cross sectional	Atopic dermatitis	To determine the prevalence of ABO blood groups and to investigate their association with dust, pollen and skin allergy.	123 young adults (males and females)	Age: 18–21 years	Blood group B is most common and has a high risk level for developing allergies (p=0.0007774).
11	Brachtel et al 34 Country: Germany Year: 1979	Case control	Atopy	To assess the association of atopic disease with blood group with reference to a new population sample and to include polymorphic systems.	239 patients 151 controls	Outpatients of the Dermatological Clinic of the University of Mainz	Higher susceptibility of individuals with blood groups A and B to atopic diseases such as rhinitis, bronchial asthma, dermatitis and many more.