Serum procalcitonin and infective exacerbations of asthma.

To the Editor

Bafadhel and colleagues report in a recent issue of CHEST (June 2011) that serum procalcitonin levels are high in patients admitted to hospital with pneumonia but not in those admitted with exacerbations of asthma or COPD. We examined the usefulness of serum procalcitonin in patients with moderate to severe exacerbations of asthma due to infections.

We recruited 25 patients (11 men) with confirmed diagnosis of asthma during what was considered an infective exacerbation (increased symptoms as measured by a seven-point Likert scale, increased sputum volume and purulence) that was not severe enough to require hospitalization. None of the patients had radiologic evidence of pneumonia. Spirometry was performed and nasopharyngeal swabs and sputum were obtained for virology, bacterial culture, and quantitative cell counts. Measurements were repeated at 1, 4, and 6 weeks until symptoms had completely resolved. Procalcitonin was measured in serum at the time of exacerbation and at 6 weeks. Procalcitonin was measured in duplicate from 50 μL of serum using a time-resolved amplified cryptate emission technology assay (Kryptor TRACE PCT; Brahms; Berlin, Germany). The lower limit of detection is 0.02 ng/mL, and the assay functional sensitivity was 0.06 ng/mL. All patients gave written informed consent, and the study was approved by the Research Ethics Board of St. Joseph's Healthcare Hamilton.

Test results in 15 subjects (60%) had positive identification of a pathogen; five (20%) were viral (one influenza B, one respiratory syncytial virus, one human metapneumovirus, and one parainfluenza 4 and rhinovirus, human coronavirus NL63), two (8%) were bacterial (Streptococcus pneumoniae and Haemophilus parainfluenzae), and four (16%) were both bacterial and viral (Moraxella and rhinovirus, Streptococcus pneumoniae and human coronavirus NL63, Streptococcus pneumonia and influenza B, and Staphylococcus aureus and parainfluenza 3).

Symptoms and FEV1 improved significantly, and the sputum cell counts returned to normal at 6 weeks (Table 1 ). However, there was no significant difference in procalcitonin levels between the initial measurement and at 6 weeks (Table 1). There were also no differences between patients who had infective vs noninfective exacerbations or those with viral vs bacterial bronchitis.

Table 1

Measurements During an Exacerbation and 6 Weeks Later

Measurement	At Exacerbation	At Resolution (6 wk)	P Value
Symptomsa	3.5 (1.2)	6.0 (7.0)	< .05
FEV1, %	60.6 (25.6)	67.0 (23.0)	< .001
Sputum TCC, 106/g	40 (9.7)	6.0 (1.5)	< .05
Sputum N, %b	72.7 (9.3–98.7)	53.7 (8–93)	< .05
Sputum E, %c	3.7 (0–70)	0.8 (0–10)	.5
Serum procalcitonin, ng/mL	0.08 (0.03)	0.08 (0.02)	.9

Values are given as mean (SD) unless otherwise noted. E = eosinophil; N = neutrophil; TCC = total cell count.

Symptoms of cough, chest tightness, wheeze, and shortness of breath were measured on a seven-point Likert score (7 best, 1 worst).

Median (interquartile range).

Median (minimum-maximum).

Our data confirm the observations of Bafadhel and colleagues that serum procalcitonin is unlikely to be useful to identify infective exacerbations of asthma. Elevated sputum total cell count with predominant neutrophilia is a more reliable indicator of an infective bronchitis.