Testing: Sputum Eosinophil Count
Airway inflammation; Sputum cell count
Sputum is a respiratory expectorant composed primarily of mucus and does not contain nasopharyngeal secretions or saliva. The sputum eosinophil count refers to the number of eosinophils in sputum, typically expressed as a percentage of the total cell count. Examination of sputum is a noninvasive way to assess for airway inflammation.
Collection and Processing
Sputum can be naturally produced via a productive cough or induced by inhaling bronchial irritants. Protocols for induced sputum typically involve 3 % hypertonic saline administered via nebulizer (AARC 1993; Pavord et al. 1997; National Jewish Health 2010). Oftentimes, patients are pretreated with a bronchodilator. The sample may then be treated with dithiothreitol (DTT), a mucolytic agent, to promote cell dispersion. The sample is centrifuged and subsequently undergoes Wright staining. The differential cell count is then obtained using bright field microscopy.
- AARC clinical practice guideline. Bland aerosol administration. American Association for Respiratory Care. Respiratory care. 1993;38(11):1196.Google Scholar
- Jeffery P. Pathology of asthma compared with chronic obstructive pulmonary disease. In: Adkinson NF, Busse WW, Bochner BS, Holgate ST, Simons FER, Lemanske RF, editors. Middleton’s allergy: principles and practice. 7th ed. St. Louis: Mosby; 2009. p. 921.Google Scholar
- Klion AD and Weller PF. Causes of pulmonary eosinophilia. In: UpToDate, Basow, DS (Ed), UpToDate, Waltham, MA, 2012.Google Scholar
- Moqbel R, Lacy P, Adamko D, Odemuyiwa S. Biology of eosinophils. In: Adkinson NF, Busse WW, Bochner BS, Holgate ST, Simons FER, Lemanske RF, editors. Middleton’s allergy: principles and practice. 7th ed. St. Louis: Mosby; 2009. p. 295.Google Scholar
- National Jewish Health Policy and Procedures. Sputum induction. http://spyderweb.njrc.org/ (2010). Accessed 28 Oct 2012.
- Petsky HL, Kynaston JA, Turner C, Li A, Cates CJ, Lasserson TJ, Chang AB. Tailored interventions based on sputum eosinophils versus clinical symptoms for asthma in children and adults. Cochrane Database Syst Rev. 2009Google Scholar
- Pizzichini E, Pizzichini MMM, Efthimiadis A, Evans S, Morris MM, Squillace D, Gleich GJ, Dolovich J, Hargreave FE. Indices of airway inflammation in induced sputum: reproducibility and validity of cell and fluid-phase measurements. Am J Respir Crit Care Med. 1996;154:308–17.PubMedCrossRefGoogle Scholar