title: Serum LDH in chronic cough: a potential marker of airway inflammation.
abstract: OBJECTIVE
  Lactate dehydrogenase (LDH) is found in almost all tissues of the body and five different isoenzymes are known (LDH-1 to LDH-5). LDH can be elevated in many pathological conditions. We have observed serum LDH to be increased in patients with chronic cough. We wanted to confirm this finding, study the reproducibility and determine the origin of the LDH.
  
  
  METHODS
  Patients prospectively seen at the Hull Cough Clinic had total and specific LDH isoenzyme levels in serum determined. A subgroup of patients also had a serum creatine phosphokinase (CK) measured. Patients completed cough symptom scores and the Hull Airway Reflux Questionnaire (HARQ). Spirometry was performed.
  
  
  RESULTS
  Eighty-three patients were included. Forty-two percent had LDH values above the reference range and 78% had LDH values in the fourth quartile of the reference range or above. This increase in LDH was predominantly because of a rise in isoenzymes 4 and 5. The increase in LDH was found to be reproducible at 8 weeks. Ten percent had CK values above the normal range. There was no correlation observed between LDH values and the cough scores, HARQ scores or lung function.
  
  
  CONCLUSIONS
  Serum LDH levels are elevated in a substantial proportion of patients with chronic cough. This rise is likely to be due to airway inflammation known to be associated with chronic cough.
authors.affiliation: Division of Cardiovascular and Respiratory Studies, Castle Hill Hospital, University of Hull, Hull York Medical School, Cottingham, UK. sfaruqi@doctors.net.uk
authors.forename: Shoaib
authors.initials: S
authors.lastname: Faruqi
authors.forename: Rachel
authors.initials: R
authors.lastname: Wilmot
authors.forename: Caroline
authors.initials: C
authors.lastname: Wright
authors.forename: Alyn Hugh
authors.initials: AH
authors.lastname: Morice
mesh_terms: D000328:Adult; D000368:Aged; D015415:Biomarkers / Q000097:blood; D016022:Case-Control Studies; D002908:Chronic Disease; D015331:Cohort Studies; D003371:Cough / Q000201:enzymology* / Q000209:etiology / Q000473:pathology*; D003402:Creatine Kinase / Q000097:blood; D005260:Female; D006801:Humans; D007770:L-Lactate Dehydrogenase / Q000097:blood*; D008297:Male; D008875:Middle Aged; D015203:Reproducibility of Results; D012720:Severity of Illness Index; D013147:Spirometry
chemical_list: D015415:Biomarkers; D007770:L-Lactate Dehydrogenase; D003402:Creatine Kinase