Assessment of hematological parameters of petrol filling workers at petrol stations in Gondar town, Northwest Ethiopia: a comparative cross-sectional study

A comparative cross-sectional study was conducted among petrol filling workers at Gondar town petrol stations in comparison with apparently healthy blood donors at the University of Gondar comprehensive specialized referral hospital blood bank. Gondar is located in the northwestern part of Ethiopia, in the Amhara region state with 180 km far from Bahir Dar, the capital city of the regional and 727 km from Addis Ababa, the capital city of Ethiopia. Based on the 2007 national census conducted by the Central Statistical Agency of Ethiopia, Gondar town has an estimated total population of 206,987 people of whom 98,085 are males and 108,902 females [19]. There are 17 petrol stations with a total of 81 workers. Of thus workers, 52 are males and 29 are females. The study was done from January to March 2019.

According to the rule of thumb that has been recommended by van Voorhis and Morgan, 30 participants per group are mandatory to detect real differences between groups, which could lead to about 80% power [20]. Therefore, 110 study subjects which comprise 55 petrol filling workers as a case and 55 healthy blood donors as control were recruited into this study. Study participants in both cases and controls were taken from the study population by a convenient sampling technique.

All petrol station workers who were exposed to petrol chemicals at Gondar town petrol stations and all apparently healthy blood donors at the University of Gondar comprehensive specialized referral hospital blood bank during the study period were as the source population for cases and controls, respectively. All petrol filling workers at Gondar town petrol stations and apparently healthy blood donors at the University of Gondar comprehensive referral hospital blood bank who fulfilled the inclusion criteria were included in the study.

All petrol filling workers with age ranges of 18–65 years who were exposed to petrol fo a minimum of one year and all petrol non-exposed apparently healthy blood donors with age ranges of 18–65 years were included in the study. However, individuals who have ever had a history of either chewing chat or smoking cigarette; reactive for human immunodeficiency virus (HIV), hepatitis B virus, and hepatitis C virus; and individuals who had a history of inherited bleeding disorders, hypertension, chronic renal disease, chronic liver disease, and malignancy were excluded from the study. In addition to this, those who were on/taking cytotoxic chemotherapy, radiotherapy, and corticosteroid medications had also been excluded from the study. Moreover, individuals who were with evidence of ill health, in the use of medications, received a blood transfusion in the last 6 months, and donated blood within the last 3 months were excluded.

Definition and classification of hematological parameters were based on the local reference ranges [21]. The normal reference range for different hematological parameters was defined as follows: RBC 3.53–6.93 × 10¹²/l for male and 3.45–6.25 × 10¹²/l for female; hematocrit (Hct) 36.2–58.6% for male and 32.1–56.6% for female; hemoglobin (Hb) 11.5–18 g/dl for male and 11.0–16.0 g/dl for female; mean cell hemoglobin concentration (MCHC) 29.5–34.4% for male 28.5–34.4% for female; and mean cell hemoglobin (MCH) 26.6–33.3 pg for male and 25.8–32.8 pg for female, respectively. On the other hand, parameters such as WBC, absolute neutrophils, absolute lymphocytes, absolute mixed cell, platelet, mean cell volume (MCV), red cell distribution width (RDW), neutrophil %, lymphocyte %, and mixed cell % were defined as 3.2–8.8 × 10⁹/l, 1.6–5.1 × 10⁹/l, 1–3.5 × 10⁹/l, 0.2–1 × 10⁹/l, 128–432 10⁹/l, 85–100 fl; 12–17%, 36–69%, 22–55%, and 0.2–1%, respectively for both adult males and females [21]. Hematological parameters below or above these pre-stated reference ranges were considered as decreased or increased in accordance.

The questionnaire was prepared in English, translated to Amharic language, and then translated back to English to check for consistency. The training was given to data collectors prior to data collection. The data were collected by trained data collectors: experienced nurses and medical laboratory technologists. The process of data collection was closely supervised by investigators.

After data was cleaned and checked for completeness, it was entered in Epi info version of 7.2.0.1 and transferred to SPSS 20.0 for analysis. Normality was checked via visual plots like the Q-Q plot, the statistical method like the Kolmogorov-Smirnov normality test, and the Shapiro-Wilk normality test. Homogeneity of variance was checked by the Levene test. For normally distributed data, the independent t test was used to compare differences in the mean of hematological parameters between cases and controls. For non-normally distributed data, the Mann-Whitney U test was used. To measure the correlation of hematological parameters with duration of exposure to petrol, the Pearson product-moment bivariate correlation for normally distributed data and Spearman’s rank-order correlation analysis for non-normally distributed data were used. The results were summarized in mean ± standard deviation (SD), median, and interquartile range (IQR). The results were presented in tables and texts. P value ≤ 0.05 was considered as statistically significant for all analysis.

The study was conducted after ethical approval was obtained from the Research and Ethical Review Committee of School of Biomedical and Laboratory Sciences, College of Medicine and Health Sciences, the University of Gondar. Support and permission letters were obtained from the Gondar town health office and from each petrol station administrative offices. Moreover, written informed consent was taken from study participants after explaining the purpose, benefits, and possible risks of this study. Participation in the study was purely on a voluntary basis. Study participants who had abnormal hematological results were linked to the University of Gondar comprehensive specialized referral hospital for better medical advice and healthcare services.

A total of 110 age- and sex-matched study participants were included in this study. The median (IQR) age was 28 (22–35) years and 29 (22-34) years for cases and controls, respectively. However, there were no statistically significant differences between case and control subjects in age (P = 0.983). Among 55 cases, the majority 41 (74.5%) were males and 28 (50.9%) were single in their marital status (Table 1).

The magnitude of leukocytosis, leukopenia, and neutropenia among petrol filling workers was 14.5%, 3.6%, and 18.2%, respectively. On the other hand, anemia and neutropenia among healthy controls were reported to be 3.6% and 7.3%, respectively (Table 2).

The mean RBC count and Hb level were significantly higher in petrol filling workers as compared with the control group. On the other hand, the mean MCV value of petrol filling workers has shown a significant decrement compared with healthy controls. Moreover, median HCT, MCHC, platelet count, absolute lymphocytes count, and RDW of petrol filling workers were higher than health controls (Table 3).

Based on the distribution of the hematological parameters, Pearson product-moment and Spearman’s rank-order bivariable correlation analyses were done for normally distributed and non-normally data, respectively (see Additional File 1). Duration of petrol exposure showed a significant positive correlation with RBC count and MCHC value. On the other hand, duration of exposure for petrol had shown a significant negative correlation with MCV result of petrol filling workers. However, other hematological parameters indicated non-significant positive correlations (Table 4). The additional files showed the scatter plot of the bivariate correlation analysis of RBC count, MCV, and MCHC with duration of exposure for petrol (see Additional File 2, Additional File 3, and Additional File 4).