Study limitations Although the main strength of this study was the size of the study population showing only a small percentage of missing values, some limitations in test administration see more and data collection selleckchem cannot be avoided. When comparing hearing threshold levels of construction workers to ISO-1999 standard values, both noise-exposed workers and controls show a deviation of about 10 dB HL at the lower frequencies. This deviation is reported in other studies as well, either in control groups used to analyse hearing ability of construction employees

(Hessel 2000; Hong 2005) or in a general occupational population (Dobie 2007). In this study, some aspects of test administration may have been responsible for this difference. The available audiometric data are retrieved from screening assessments, omitting measurements of bone conduction. Therefore,

www.selleckchem.com/products/acalabrutinib.html we cannot correct for the presence of possible conductive hearing losses (e.g. due to permanent middle ear problems or temporarily conductive losses caused by a cold) that may be responsible for the elevated thresholds at the lower frequencies. Moreover, audiometric measurements are carried out on location in a mobile unit equipped with a soundproof booth. Nevertheless, possible exposure to background noise during the hearing test, which could produce elevated thresholds at 0.5 kHz, and to a lesser extent at 1 kHz (Suter 2002), cannot be ruled out completely. Furthermore, in this study no fixed noise-free period prior to audiometric measurements is defined. However, minimal time between possible occupational noise exposure

and hearing tests was 2–3 h. Guidelines in literature recommend a longer noise-free period, varying from 6 to 14 h (NCvB 1999; May 2000). Consequently, the noise-free period of 2–3 h may not be sufficient to fully recover from a possible temporary threshold shift (TTS) (Melnick 1991; Strasser et al. 2003), and a complete absence of TTS cannot be guaranteed. Moreover, collecting the appropriate data for noise exposure in this large population appears to be another limitation in this study. This study lacks individually measured noise exposure levels. Because construction workers are highly mobile and perform several different tasks, it is extremely difficult to obtain accurate estimates of the individual noise exposure learn more levels. Noise exposure estimations Although regression analyses confirm a significant relationship between noise intensity and PTA-values, the hearing thresholds increase only marginal with increasing noise exposure level. This relationship follows a much flatter curve than predicted by ISO-1999. A previous examination of Dutch industry workers compared single frequency threshold levels to ISO predictions (Passchier-Vermeer 1986) and obtained a similar pattern, suggesting that ISO underestimates hearing loss at lower exposure levels and overestimates hearing loss at higher noise levels.