Between-observer repeatability of sputum differential cell counts. Influence of cell viability and squamous cell contamination

Sputum processing by mechanical dissociation: A rapid alternative to traditional sputum assessment approaches

BACKGROUND

Sputum cytology is currently the gold standard to evaluate cellular inflammation in the airways and phenotyping patients with airways diseases. Sputum eosinophil proportions have been used to guide treatment for moderate to severe asthma. Furthermore, raised sputum neutrophils are associated with poor disease control and impaired lung function in both asthma and COPD and small airways disease in cystic fibrosis. However, induced-sputum analysis is subjective and resource heavy, requiring dedicated specialist processing and assessment; this limits its utility in most clinical settings. Indirect blood eosinophil measures have been adopted in clinical care. However, there are currently no good peripheral blood biomarkers of airway neutrophils. A resource-light sputum processing approach could thus help integrate induced sputum more readily into routine clinical care. New mechanical disruption (MD) methods can rapidly obtain viable single cell suspensions from sputum samples.

AIMS

The aim of this study was to compare MD sputum processing to traditional methods for cell viability, granulocyte proportions and sputum cytokine analysis.

METHODS

Sputum plugs were split and processed using traditional methods and the MD method, and samples were then compared.

RESULTS

The MD method produced a homogeneous cell suspension in 62 s; 70 min faster than the standard method used. No significant difference was seen between the cell viability (p = 0.09), or the concentration of eosinophils (p = 0.83), neutrophils (p = 0.99) or interleukin-8 (p = 0.86) using MD.

CONCLUSION

This cost-effective method of sputum processing could provide a more pragmatic, sustainable means of directly monitoring the airway milieu. Therefore, we recommend this method be taken forward for further investigation.

Assessment of a rapid liquid-based cytology method for measuring sputum cell counts

Differential sputum cell counting is not widely available despite proven clinical utility in the management of asthma. We compared eosinophil counts obtained using liquid-based cytology (LBC), a routine histopathological processing method, and the current standard method. Eosinophil counts obtained using LBC were a strong predictor of sputum eosinophilia (≥3%) determined by the standard method suggesting LBC could be used in the management of asthma.

Eosinophilia in Pulmonary Disorders

Lung disease associated with marked peripheral blood eosinophilia is unusual and nearly always clinically significant. Once recognized, it is generally easy to manage, albeit with long-term systemic corticosteroids. A failure to respond to oral steroids in the context of good compliance suggests a malignant cause for the eosinophilia. An important development is the introduction of antieosinophil therapies, particularly those directed against the interleukin 5 pathway, which is hoped to provide benefit in the full spectrum of eosinophilic lung disease as well as asthma, reducing the burden of side effects and resultant comorbidities.

Short-term reproducibility of the inflammatory phenotype in different subgroups of adult asthma cohort

Inflammatory phenotype classification using induced sputum appears attractive as it can be applied to inflammation-based management of the patients with asthma. The aim of the study was to determine the reproducibility of inflammatory phenotype over time in patients with asthma. In 66 adults asthma was categorized as steroid-naïve (SN, n = 17), mild to moderate (MMA, n = 33), and refractory treated with oral corticosteroids (RA, n = 16). Clinical assessment, skin prick testing, spirometry, and two sputum inductions in 4-6-week interval were done. Inflammatory phenotypes were classified as eosinophilic (EA), consisting of eosinophilic and mixed granulocytic phenotypes, and noneosinophilic (NEA) consisting of paucigranulocytic and neutrophilic phenotypes. During study asthma treatment remained constant. In SN group 25% of patients changed phenotype from EA to NEA and 44% changed phenotype from NEA to EA. In MMA group 26% of patients changed phenotype from EA to NEA and 50% changed phenotype from NEA to EA. In 29% of RA patients inflammatory phenotype changed from EA to NEA and in 22% it changed from NEA to EA. Inflammatory classification, using induced sputum, is not fully reproducible in adults with asthma in short-term evaluation. EA seems to be more stable phenotype across all subgroups whereas NEA remained stable only in RA group.

Reliability of a rapid hematology stain for sputum cytology

Objective:

To determine the reliability of a rapid hematology stain for the cytological analysis of induced sputum samples.

Methods:

This was a cross-sectional study comparing the standard technique (May-Grünwald-Giemsa stain) with a rapid hematology stain (Diff-Quik). Of the 50 subjects included in the study, 21 had asthma, 19 had COPD, and 10 were healthy (controls). From the induced sputum samples collected, we prepared four slides: two were stained with May-Grünwald-Giemsa, and two were stained with Diff-Quik. The slides were read independently by two trained researchers blinded to the identification of the slides. The reliability for cell counting using the two techniques was evaluated by determining the intraclass correlation coefficients (ICCs) for intraobserver and interobserver agreement. Agreement in the identification of neutrophilic and eosinophilic sputum between the observers and between the stains was evaluated with kappa statistics.

Results:

In our comparison of the two staining techniques, the ICCs indicated almost perfect interobserver agreement for neutrophil, eosinophil, and macrophage counts (ICC: 0.98-1.00), as well as substantial agreement for lymphocyte counts (ICC: 0.76-0.83). Intraobserver agreement was almost perfect for neutrophil, eosinophil, and macrophage counts (ICC: 0.96-0.99), whereas it was moderate to substantial for lymphocyte counts (ICC = 0.65 and 0.75 for the two observers, respectively). Interobserver agreement for the identification of eosinophilic and neutrophilic sputum using the two techniques ranged from substantial to almost perfect (kappa range: 0.91-1.00).

Conclusions:

The use of Diff-Quik can be considered a reliable alternative for the processing of sputum samples.

Reproducibility of sputum differential cell counts is not affected by squamous epithelial cells

OBJECTIVE

Induced sputum is used to assess markers of inflammation in asthmatic individuals, and sputum cell differential counts provide an outcome to evaluate the presence, type, and degree of inflammation in the airways. Contamination of sputum slides with squamous epithelial cells (SECs) has been reported to adversely affect the reproducibility of sputum cell differential counts; however, this has not been studied in a controlled manner. Excluding sputum slides because of excessive squamous cell contamination can be problematic resulting in under-powering of studies. The aim of this study is to evaluate the effect of SEC contamination and cell dispersion on the reproducibility of differential counts of sputum cells prepared on glass slides.

STUDY DESIGN

A total of 33 sputum samples were induced from 11 subjects with mild asthma under baseline conditions and following an allergen inhalation challenge. Mucoid and salivary portions of each sample were divided and processed in parallel. To evaluate the effect of increasing the proportion of SEC and to evaluate the effect of increasing the number of leukocytes per high power field (HPF), four slides with varying leukocyte numbers and SEC percentages were prepared from each sample by combining and adjusting the volume of cell suspensions derived from mucous and saliva. The four slides were prepared to fall in the following categories: (A) 50 cells/HPF and <20% SEC; (B) 50 cells/HPF and >20% SEC; (C) 100 cells/HPF and <20% SEC; and (D) 100 cells/HPF and >20% SEC. All slides were blinded and counted twice by an experienced observer, and twice by an inexperienced observer.

RESULTS

The differential cell counts for eosinophils, macrophages, and neutrophils were highly reproducible under all conditions when enumerated by an experienced observer (ICC > 0.9), and furthermore, SEC contamination did not affect ICC when differential counts were enumerated by an inexperienced observer (ICC > 0.8).

CONCLUSION

Our results demonstrate that slides containing SECs, up to 40% in this study, have reproducible differential cell counts.

Inflammatory phenotypes in adult asthma: clinical applications

BACKGROUND

The pattern of granulocyte infiltration can be used to identify different inflammatory phenotypes in asthma. Recognized granulocyte phenotypes using induced sputum are eosinophilic (EA), neutrophilic, mixed granulocytic and paucigranulocytic asthma.

METHODS

The recognition and importance of inflammatory phenotype analysis using induced sputum in adult asthma are reviewed using published literature.

RESULTS

Knowledge of inflammatory phenotype is useful because it relates to treatment response, mechanistic pathways involved in disease pathogenesis and future disease risk. The population attributable risk of asthma because of eosinophilic inflammation is about 50%, and conversely, this means that up to 50% of asthma cannot be attributed to eosinophilic inflammation, and represents asthma associated with non-eosinophilic processes. In these patients, bronchial biopsy shows significantly fewer eosinophils in the bronchial mucosa than subjects with EA. This confirms that non-eosinophilic asthma is a consistent pattern/phenotype in the airway lumen and the airway mucosa. A key aspect of asthma inflammatory phenotype analysis is that it can be applied to individual patients. The underlying principle relates to the association between a clinical response to corticosteroids and the presence of a selective sputum eosinophilia.

CONCLUSIONS

Clinically useful applications of induced sputum analysis are the detection of non-adherence to corticosteroid therapy, assessment of adequacy of inhaled corticosteroid therapy, long-term therapy management in asthma, oral corticosteroid dose adjustment in refractory asthma and assessment of occupational asthma.

Airway biomarkers of the oxidant burden in asthma and chronic obstructive pulmonary disease: current and future perspectives

The pathogenesis of asthma and chronic obstructive pulmonary disease (COPD) has been claimed to be attributable to increased systemic and local oxidative stress. Detection of the oxidant burden and evaluation of their progression and phenotypes by oxidant biomarkers have proved challenging and difficult. A large number of asthmatics are cigarette smokers and smoke itself contains oxidants complicating further the use of oxidant biomarkers. One of the most widely used oxidant markers in asthma is exhaled nitric oxide (NO), which plays an important role in the pathogenesis of asthma and disease monitoring. Another oxidant marker that has been widely investigated in COPD is 8-isoprostane, but it is probably not capable of differentiating asthma from COPD, or even sensitive in the early assessment of these diseases. None of the current biomarkers have been shown to be better than exhaled NO in asthma. There is a need to identify new biomarkers for obstructive airway diseases, especially their differential diagnosis. A comprehensive evaluation of oxidant markers and their combinations will be presented in this review. In brief, it seems that additional analyses utilizing powerful tools such as genomics, metabolomics, lipidomics, and proteomics will be required to improve the specificity and sensitivity of the next generation of biomarkers.

Inflammatory mediators in exhaled breath, induced sputum and saliva

BACKGROUND AND OBJECTIVE

Airway inflammation is assessed to monitor progression, control and treatment of asthma. The collection of exhaled breath condensate (EBC) provides a non-invasive alternative to induced sputum samples for the monitoring of airway inflammation. Both samples can be confounded by salivary contamination. The aim of this study was to compare the levels of inflammatory mediators in samples of EBC, induced sputum and saliva samples from subjects with asthma.

METHOD

EBC, saliva and induced sputum samples were collected from subjects with asthma (n=10). Total protein, IL-8, 8-isoprostane and surfactant protein A (SPA) were assessed in each sample.

RESULTS

Total protein, IL-8, 8-isoprostane and SPA were detected in all sputum samples. Only total protein and SPA were consistently measured in EBC, with levels at least 100-fold lower than those measured in induced sputum. In saliva, total protein, SPA and 8-isoprostane were detected in all samples, with IL-8 detected in 60% of samples.

CONCLUSIONS

Induced sputum is a reliable technique that can be used to assess markers of airway inflammation. While EBC is a simple and inexpensive technique to collect lower airway secretions, the detection of inflammatory mediators is variable, and further work is required to validate this technique to assess inflammatory mediators.

Optimization of the conditions for preservation of induced sputum: influence of freezing on cellular analysis

BACKGROUND

Induced sputum (IS) analysis is a noninvasive, valid, and reproducible method for evaluating airway inflammation. It has been suggested that freezing of IS samples in order to delay analysis is feasible. However, the optimal conditions for preservation of IS samples have not been determined.

OBJECTIVES

To determine optimal freezing conditions of IS samples, ensuring adequate specimen quality for assessment of cell viability, total cell count, and differential cell count.

SUBJECTS AND METHODS

Twenty-one subjects were enrolled: 6 healthy control subjects, 5 patients with allergic rhinitis, 5 patients with mild asthma, and 5 patients with severe asthma. Each came to the laboratory once for IS sampling. Cell plugs were homogenized with dithiothreitol and separated into 12 aliquots. Viability and total and differential cell counts were determined for each aliquot. Bovine serum albumin (BSA) with dimethylsulfoxide (DMSO) was added to half of the aliquots, and fetal bovine serum (FBS) with DMSO was added to the other half. One half of the aliquots containing BSA or FBS were frozen at -20 degrees C, and the other half were frozen at - 80 degrees C. After 3, 7, or 10 days, samples were thawed and total cell counts, viability, and differential cell counts were assessed.

RESULTS

Slide quality and total cell counts did not vary significantly according to freezing duration, temperature, or medium when compared to nonfrozen control samples. With FBS at -80 degrees C, cell viability did not vary significantly between control samples and freezing for 3, 7, and 10 days (59% vs 54%, 59% vs 54%, and 58% vs 54%, respectively; p > 0.05), whereas every other condition showed a significant decrease. Freezing did not affect the eosinophil percentage significantly.

CONCLUSION

Freezing of IS samples in FBS with DMSO at - 80 degrees C allows adequate preservation of IS specimens. Samples can be kept for at least 10 days in those conditions without significantly altering total cell counts, viability, and eosinophil percentage.

Induced sputum in the investigation of airway inflammation of COPD

During the last decade, the method of sputum induction (SI) has offered the opportunity to study inflammation in patients with chronic obstructive pulmonary disease (COPD). This paper reviews methodological aspects of SI and summarizes its uses in the research of inflammation in COPD, including sputum cellularity and soluble markers. SI is a relatively safe, reliable, and reproducible technique, used to investigate different aspects of airway inflammation. Although various methods of induction and processing have been proved safe and highly reproducible, a generally accepted method is needed. Sputum analysis has given evidence for increased numbers of macrophages and neutrophils in COPD patients compared to normal subjects. In some studies, increased numbers of eosinophils have been also reported. Changes in various mediators have been found in sputum supernatant of COPD patients (IL-8, LTB-4 and TNF-a). The clinical usefulness of the method in the follow-up of the disease has not been explored extensively. A number of observations in patients with different clinical characteristics could be proven useful in identifying patterns of inflammation associated with different prognosis. Finally, SI could also guide treatment; such as, sputum eosinophilia in COPD could predict response to inhaled corticosteroids.

Induced sputum is a reproducible method to assess airway inflammation in asthma

To evaluate the reproducibility of induced sputum analysis, and to estimate the sample size required to obtained reliable results, sputum was induced by hypertonic saline inhalation in 29 asthmatic subjects on two different days. The whole sample method was used for analysis, and inflammatory cells were counted on cytospin slides. Reproducibility, expressed by intra-class correlation coefficients, was good for macrophages (+0.80), neutrophils (+0.85), and eosinophils (+0.87), but not for lymphocytes (+0.15). Detectable differences were 5.5% for macrophages, 0.6% for lymphocytes, 5.2% for neutrophils, and 3.0% for eosinophils. We conclude that analysis of induced sputum is a reproducible method to study airway inflammation in asthma. Sample sizes greater than ours give little improvement in the detectable difference of eosinophil percentages.

Sputum processing: a new method to improve cytospin quality

BACKGROUND

Sputum examination is being increasingly used as a non-invasive method for studying airway inflammation. However, the application of sputum still presents some methodological problems and the results of sputum analysis may be substantially flawed by salivary contamination, cell and mucus debris. In addition, much work is needed to deepen the possibility of extensive application of cell and molecular biology techniques to sputum analysis.

OBJECTIVE

In an attempt to improve the technique of sputum processing, we investigated the effect of: (i) 20 and 11 microm filtration in addition to 40 microm on salivary contamination; (ii) Percoll density gradient centrifugation on sputum slides quality; (iii) a culture medium (Minimum Essential Medium containing HEPES 22 mm, pH 7.4: MEM) as washing and suspension solution compared to PBS on cell viability.

METHODS

Induced sputum samples were obtained in 37 asthmatics. 21 samples were processed as selected sputum and 16 samples as entire expectorates. After dithiotreitol (DTT) homogenization, each specimen was aliquoted in two parts of equal volume. One portion was processed with the usual method, the other using a modified method: cell pellet was suspended in sterile MEM, filtered through 40, 20 and 11 microm net filters and separated from the residual debris by Percoll gradient centrifugation.

RESULTS

As compared to the current sputum processing this method resulted in: (i) no selective bronchial cellular loss; (ii) a significant decrease of salivary contamination, particularly in entire expectorates in which squamous cells were reduced from 47 (36) to 15.5% (20) as median values and interquartile range; (iii) a higher proportion of good quality cytospins; (iv) maintenance of cell viability over the time (88% vs. 81% in MEM and PBS, respectively) 1 h after sample collection.

CONCLUSION

In the present study we demonstrated that the proposed method is feasible and makes it possible to overcome most of the technical limits met with the commonly used method, pointing to a potential extension of induced sputum application for more sophisticated techniques.

Measurement of airway inflammation in asthma

Chronic airway inflammation is considered responsible for symptoms and disorders of airway function associated with asthma. This process is the target of anti-inflammatory therapy, so a number of standardized, noninvasive techniques have been developed to assess it. More recent approaches include the measurement of exhaled gases and nonvolatile substances in breath condensate. Results from studies using a wide variety of inflammatory markers have shown group differences between patients with asthma and healthy control subjects, but evidence for the diagnostic use of these markers in individual patients is scarce. Similarly, despite many studies demonstrating some correlation between markers of airway inflammation and a measure of disease control, none has yet convincingly shown a place for the use of these markers in an individual with corticosteroid-treated asthma. However, application of these markers continues to further our understanding of the disease process and provides the potential for more appropriate, customized therapy.

Induced sputum and other outcome measures in chronic obstructive pulmonary disease: safety and repeatability

The forced expiratory volume in 1 sec (FEV1) is the most established outcome measure in chronic obstructive pulmonary disease (COPD). However, changes in FEV1 in response to treatment are small in relation to the repeatability of the measurement and there is increasing interest in other measures including markers of lower airway inflammation in induced sputum, assessment of symptoms and health status using visual analogue scores, and questionnaires. Little is known about the repeatability of these measures or the safety of sputum induction in COPD. We have assessed the safety of sputum induction in 61 subjects with moderate and severe COPD who participated in a placebo-controlled cross-over study The within-subject repeatability of sputum markers of airway inflammation, health status using the chronic respiratory disease questionnaire (CRQ) and symptom visual analogue scores (VAS) were estimated from the data obtained from before and after 2 weeks of treatment with placebo. Sputum induction was performed on 122 occasions and was successful resulting in a cytospin adequate to assess a differential cell count in 95% of inductions. The group mean (SEM) FEV1 was 1.09 (0.05)[41.6 (2.9)% predicted] and the mean (SEM) fall in FEV1 after sputum induction was 120 ml (6) and % fall 10.9% (0.55%). Seven inductions were stopped due to a fall in FEV1 >20% and at a further 13 visits the full sputum induction protocol was not completed due to development of symptoms. The reproducibility of measurements, calculated by the intra-class correlation coefficient, was relatively high for all indices measured (0.4-0.95) with the exception ofthe proportion of lymphocytes (0.15) and epithelial cells (0.3). The ICC for symptom scores and the CRQ domains ranged between 0.87 and 0.96. In conclusion, sputum induction is safe and the cell and fluid phase mediators repeatable in the investigation of airway inflammation in patients with COPD. VAS symptom scores and the CRQ are reproducible outcome measures in COPD.

The use of sputum cell counts to evaluate asthma medications

Total and differential cell counts from hypertonic-induced, dithiothreitol-dispersed sputum provide reproducible measurements of airway inflammatory cell counts, which are responsive to treatment with anti-inflammatory drugs. They have helped to understand the kinetics of inflammatory cell changes in asthma after the reduction of corticosteroids and the subsequent re-introduction of treatment. They have identified that the presence of sputum eosinophilia in asthma, chronic cough and chronic airflow limitation is a predictor of steroid-responsiveness and of lack of 'asthma control'. They can be used to study the dose-response effect of inhaled corticosteroids and may be useful to establish the relative potency of different corticosteroid formulations and delivery devices. Sputum cell counts are also useful to study the potential anti-inflammatory effects of drugs like theophylline, long-acting beta-adrenoceptor agonists, leukotriene antagonists and newer drugs in development. They may be helpful to select add-on therapy to corticosteroids in 'difficult-to-control' asthma.

Induced sputum cell counts in healthy adults

Induced sputum cell counts provide a relatively noninvasive method to evaluate the presence, type, and degree of inflammation in the airways of the lungs. Their interpretation requires a knowledge of normal values from a healthy population. The objective was to examine the total and differential cell counts in induced sputum from a sample of healthy adults. A total of 118 healthy nonsmoking adults were studied. None had asthma or airflow obstruction (negative history, FEV(1) >/= 80% predicted, ratio of FEV(1) to vital capacity [FEV(1)/VC] >/= 80%, methacholine PC(20) >/= 16 mg/ml). Forty-six were atopic. Sputum induction produced an adequate sample in 96 subjects [53 males, mean age (range) 36 (18 to 60) yr]. The expectorate was processed within 2 h; sputum was selected, treated with dithiothreitol, filtered, and examined in a hemocytometer for total cell count and viability and on Wright-stained cytospins for a differential cell count. The mean, median (90th percentile) total cell count was 4.1, 2.4 (9.7) x 10(6) cells/g and cell viability was 69.6, 72.0 (89.7)%. The proportions of eosinophils were 0.4, 0.0 (1.1)%, neutrophils 37.5, 36.7 (64.0)%, macrophages 58.8, 60.8 (86.1)%, lymphocytes 1.0, 0.5 (2.6)%, metachromatic cells 0.0, 0.0 (0.04)%, and bronchial epithelial cells 1.6, 0.3 (4.4)%, respectively. Female gender and atopy were associated with a significant elevation of eosinophils; mean difference between male/female was 0.3% (p = 0.043) and between atopic/nonatopic 0.4% (p = 0.024). This study has identified reference values for total and differential cell counts in induced sputum of healthy adults.

Effect of inhaled ozone on exhaled nitric oxide, pulmonary function, and induced sputum in normal and asthmatic subjects

BACKGROUND

Nitric oxide (NO) may have a role in the pathophysiology of tissue injury in response to inhaled ozone in animals.

METHODS

A double blind, randomised, placebo controlled, crossover study was undertaken to investigate the effects of inhaled ozone in 10 normal and 10 atopic asthmatic volunteers. Subjects were exposed to 200 ppb ozone or clean air for four hours with intermittent exercise, followed by hourly measurement of spirometric parameters and exhaled NO for four hours. Nasal NO and methacholine reactivity were measured and exhaled breath condensate and induced sputum samples were collected four and 24 hours after exposure.

RESULTS

Exposure to ozone caused a fall in forced expiratory volume in one second (FEV(1)) of 7% in normal subjects (p<0.05) and 9% in asthmatic subjects (p<0.005). There was a 39% increase in sputum neutrophils at four hours in normal subjects (p<0.05) and a 35% increase at four hours in asthmatic subjects, remaining high at 24 hours (p<0.005 and p<0.05, respectively). There were no differences between normal and asthmatic subjects. There were no changes in methacholine reactivity, exhaled or nasal NO, nitrite levels in exhaled breath condensate, or sputum supernatant concentrations of interleukin 8, tumour necrosis factor alpha, or granulocyte-macrophage colony stimulating factor in either group.

CONCLUSIONS

Exposure to 200 ppb ozone leads to a neutrophil inflammatory response in normal and asthmatic subjects but no changes in exhaled NO or nitrite levels.