Background: To evaluate the diagnostic accuracy of clinical signs and symptoms, C-reactive protein (CRP) and spirometric parameters and determine their interrelation in patients suspected to have an obstructive airway disease (OAD) in primary care.
Methods: In a cross sectional diagnostic study, 60 adult patients coming to the general practitioner (GP) for the first-time with complaints suspicious for obstructive airway disease (OAD) underwent spirometry. Peak expiratory flow (PEF)-variability within two weeks was determined in patients with inconspicuous spirometry. Structured medical histories were documented and CRP was measured. The reference standard was the Tiffeneau ratio (FEV1/VC) in spirometry and the PEF-variability. OAD was diagnosed when FEV1/VC < or = 70% or PEF-variability > 20%.
Results: 37 (62%) patients had OAD. The best cut-off value for CRP was found at 2 mg/l with a diagnostic odds ratio (OR) of 4.4 (95% CI 1.4-13.8). Self-reported wheezing was significantly related with OAD (OR 3.4; CI 1.1-10.3), whereas coughing was inversely related (OR 0.2; CI 0.1-0.7). The diagnostic OR of CRP increased when combined with dyspnea (OR 8.5; 95% CI 1.7-42.3) or smoking history (OR 8.4; 95% CI 1.5-48.9). CRP (p = 0.004), FEV1 (p = 0.001) and FIV1 (p = 0.023) were related with the severity of dyspnea. CRP increased with the number of cigarettes, expressed in pack years (p = 0.001).
Conclusion: The diagnostic accuracy of clinical signs and symptoms was low. The diagnostic accuracy of CRP improved in combination with dyspnea and smoking history. Due to their coherence with the severity of dyspnea and number of cigarettes respectively, CRP and spirometry might allow risk stratification of patients with OAD in primary care. Further studies need to be done to confirm these findings.