Hematoidin crystals in sputum smears: Cytopathology and clinical associations

There has been limited correlation of hematoidin crystals (HC) in sputum with clinical and diagnostic characteristics, partly because they are difficult to recognize. The aim of this study was, therefore, to assess these relationships in a consecutive cohort of sputum samples from patients submitted to a cytology laboratory.

Adequate sputum samples from 489 individuals were enrolled in this study. These were fixed in ethanol, stained by the Papanicolaou method and examined microscopically. The normality of the distribution of the continuous variable (age in years) was examined using the Shapiro-Wilk normality test. As the data were not normally distributed, Kendall rank correlation was used to correlate age with the presence of HC. The Pearson's Chi-square test was used to determine if the proportion of cases with the presence of HC was different among the categorical data variables. A univariate binary logistic regression was used to determine the variables most strongly associated with HC presence. The results include odds ratios, 95% confidence intervals, Wald χ² statistics, and corresponding P values, with statistical significance assumed at P ≤ 0.05. Analyses were performed using IBM SPSS Statistics 22.

The presence of HC in sputum was associated with increasing age (P < 0.01), current smoking (P < 0.001), chronic occupational exposure to dust (P = 0.001), and hemoptysis (P < 0.001). These crystals were most prevalent in patients with a diagnosis of carcinoma (93.9%), bronchiectasis (48%), silicosis (16.0%), and chronic obstructive pulmonary disease (0.8%). Crystals were not found in patients with acute bronchitis, asthma, or lung infections, including viral and bacterial pneumonia.

There are clear associations linked to the finding of HC in sputum that may be helpful in pointing to a specific diagnosis, such as the possibility of underlying carcinoma.