Blood eosinophil count and prospective annual asthma disease burden: a UK cohort study.
BACKGROUND
Elevated sputum eosinophil counts predict asthma exacerbations and responsiveness to inhaled corticosteroids but are impractical to measure in primary care. We investigated the relation between blood eosinophil count and prospective annual asthma outcomes for a large UK cohort.


METHODS
This historical cohort study used anonymised medical record data to identify primary care patients with asthma aged 12-80 years with 2 years of continuous records, including 1 year before (baseline) and 1 year after (outcome) their most recent eosinophil count. Negative binomial regression was used to compare outcome exacerbation rates and logistic regression to compare odds of asthma control for patients with blood eosinophil counts of 400 cells per μL or less versus greater than 400 cells per μL, adjusting for age, sex, body-mass index, smoking status, and Charlson comorbidity index. The study is registered at ClinicalTrials.gov, number NCT02140541.


RESULTS
Overall, 20 929 (16%) of 130 248 patients had blood eosinophil counts greater than 400 cells per μL. During the outcome year, these patients experienced significantly more severe exacerbations (adjusted rate ratio [RR] 1·42, 95% CI 1·36-1·47) and acute respiratory events (RR 1·28, 1·24-1·33) than those with counts of 400 cells per μL or less. They also had significantly lower odds of achieving overall asthma control (OR 0·74, 95% CI 0·72-0·77), defined as limited reliever use and no asthma-related hospital attendance or admission, acute course of oral corticosteroids, or prescription for antibiotics. Exacerbation rates increased progressively with nine ascending categories of blood eosinophil count as compared with a reference category of 200 cells per μL or less.


CONCLUSIONS
Patients with asthma and blood eosinophil counts greater than 400 cells per μL experience more severe exacerbations and have poorer asthma control. Furthermore, a count-response relation exists between blood eosinophil counts and asthma-related outcomes. Blood eosinophil counts could add predictive value to Global Initiative for Asthma control-based risk assessment.


BACKGROUND
Teva Pharmaceuticals.
Academic Primary Care, University of Aberdeen, Aberdeen, UK; Research in Real-Life, Cambridge, UK. Electronic address: dprice@rirl.org.
David B
DB
Price
Research in Real-Life, Cambridge, UK.
Anna
A
Rigazio
Department of Clinical Pharmacy, Pharmaceutical Outcomes Research, University of Colorado School of Pharmacy, Aurora, CO, USA.
Jonathan D
JD
Campbell
Center for Genomics and Personalized Medicine Research, Wake Forest School of Medicine, Winston-Salem, NC, USA.
Eugene R
ER
Bleecker
King's College London, London, UK.
Christopher J
CJ
Corrigan
Primary Care and Population Sciences, and NIHR Southampton Respiratory Biomedical Research Unit, University of Southampton, Southampton, UK.
Mike
M
Thomas
University of Pittsburgh Asthma Institute at UPMC, Division of Pulmonary, Allergy and Critical Care Medicine, Pittsburgh, PA, USA.
Sally E
SE
Wenzel
Norwich Medical School, University of East Anglia, Norwich, UK.
Andrew M
AM
Wilson
Respiratory, Global Medical Affairs, TEVA Pharmaceuticals, Frazer, PA, USA.
Mary Buatti
MB
Small
Respiratory, Global Medical Affairs, TEVA Pharmaceuticals, Frazer, PA, USA.
Gokul
G
Gopalan
Research in Real-Life, Cambridge, UK.
Valerie L
VL
Ashton
Research in Real-Life, Cambridge, UK.
Anne
A
Burden
Research in Real-Life, Cambridge, UK.
Elizabeth V
EV
Hillyer
Research in Real-Life, Cambridge, UK.
Marjan
M
Kerkhof
Respiratory Medicine Unit, Nuffield Department of Medicine, University of Oxford, Oxford, UK.
Ian D
ID
Pavord
D000293:Adolescent; D000305:Adrenal Cortex Hormones / Q000627:therapeutic use; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D018927:Anti-Asthmatic Agents / Q000627:therapeutic use*; D000900:Anti-Bacterial Agents / Q000627:therapeutic use; D001249:Asthma / Q000097:blood* / Q000188:drug therapy / Q000473:pathology; D015415:Biomarkers / Q000097:blood; D002648:Child; D015331:Cohort Studies; D017281:Cost of Illness; D018450:Disease Progression; D004804:Eosinophils; D005260:Female; D006801:Humans; D007958:Leukocyte Count; D008297:Male; D008875:Middle Aged; D011237:Predictive Value of Tests; D012044:Regression Analysis; D006113:United Kingdom; D055815:Young Adult
D000305:Adrenal Cortex Hormones; D018927:Anti-Asthmatic Agents; D000900:Anti-Bacterial Agents; D015415:Biomarkers