Pulmonary inflammatory mediators are constant within patients in Chronic Obstructive Pulmonary Disease (COPD) during the stable state.

Elizabeth Sapey, MBBS, BSc1, Diane Griffiths RGN1, Darren Bayley, MPhil1, A Ahmad PhD 1 Paul Newbold, PhD2 and Robert A Stockley, DSc1.

 

1 Lung Investigation Unit,

Birmingham University,

Birmingham,

United Kingdom

B15 2TT

 

2 Research and Development,

AstraZeneca,

Charnwood,

Leicestershire,

United Kingdom.

Little is understood about intra-patient variability in inflammation in stable COPD.  Sputum is diluted by oropharyngeal secretions and by exudation of plasma proteins but the effect of dilution on intra-patient variability has not been assessed.   

Methods:
18 patients with GOLD stage 3 COPD provided sputum and blood on 11 occasions over 4 weeks. Samples were processed to obtain cell counts and concentrations of inflammatory mediators. Salivary contamination was excluded by quantifying the percentage of squamous cells.  Assays were validated to quantify variability in detection of mediators. Exacerbations were excluded using repeated spirometry and validated daily diary cards.

Results:
All sputum samples contained less than 10% squamous cells.  Intra-assay variability in mediator detection was approximately 10%. There was notable intra-patient variability in all inflammatory indices. Significant reductions in variability were achieved by correcting for the sputum:serum albumin ratio. Overall, the mean intra-patient CV across all mediators before correction was 123% (SEM 27.4) and after was 12% (SEM 1.8): p = 0.012. 

Conclusion
There is significant intra-patient variability in measured inflammatory indices in stable COPD. This variability can be reduced by correcting for the sol: serum albumin ratio.  The remaining variability may reflect the intra-assay variation in the detection of mediator concentrations.

 

 

 

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