Screening to Promote Early Detection | 173
three-quarters of persons do not receive regular checkups (El Bcheraoui et al. 2015b). Physical exams often include both screening, such as blood pressure checks, and referrals for screening that takes place elsewhere, such as mammography and colonoscopy. The low uptake of screening may be caused in part by the generally low uptake of physical exams. It is not known, however, whether persons who do not receive regular checkups at primary care clinics get screened at other health facilities. Many Saudi Arabians know little about screening. In a survey of healthy individuals in Riyadh, a significant share of respondents (43 percent) said that screening for colon cancer should begin only after symptoms are evident (which is incorrect, as screening should be done before symptoms are evident) (Zubaidi et al. 2015). Fewer than 20 percent of respondents knew that polyps are a risk factor for colorectal cancer. Only 35 percent of respondents knew that individuals with a family history of colorectal cancer are at increased risk of colorectal cancer. Some persons have an aversion to cancer screening. Fear of pain, fear of discomfort, and fear of discovering disease all appear to be factors suppressing the uptake of colorectal cancer screening (Teixeira et al. 2018).
EFFECTIVENESS OF SCREENING Evidence supporting the implementation of screening programs varies in quality. Some types of colorectal cancer screening, including fecal occult blood tests and flexible sigmoidoscopy, have been shown to improve health outcomes in large randomized control trials (RCTs)—the gold standard of evidence (Lindholm, Brevinge, and Haglind 2008). Low-dose computed tomography (CT) screening is not recommended for the population as a whole, but RCTs in high-risk smokers and former smokers have found that CT screening reduces lung cancer mortality by 20 percent or more (de Koning et al. 2020; National Lung Screening Trial Research Team 2011). Observational studies have shown that other types of screening, such as colonoscopies (Baxter et al. 2012; Zauber et al. 2012), reduce mortality dramatically. There are no RCTs showing that screening for high blood glucose, high blood pressure, or abnormal blood lipids improves long-term health outcomes (Dyakova et al. 2016; Schmidt et al. 2020; Waugh et al. 2013), but it is widely accepted that these screenings increase the likelihood of early diagnosis and that early treatment can improve intermediate outcomes, which in turn should reduce the long-term risk of cardiovascular disease (Gillies et al. 2008; Herman et al. 2015; Kahn et al. 2010; Musini et al. 2019; Siu and US Preventive Services Task Force 2015a, 2015b). Similarly, there is no direct evidence that screening for gestational diabetes improves health o utcomes (Fitria, van Asselt, and Postma 2019). However, screening increases early diagnosis and treatment, and RCTs have shown that treatment (diet modification, glucose monitoring, and insulin if needed) reduces the risk of preeclampsia, shoulder dystocia, and macrosomia (Crowther et al. 2005; Landon et al. 2009; US Preventive Services Task Force 2013), suggesting that screening for gestational diabetes is effective. Evidence of screening effectiveness is strongest for colorectal cancer, high blood sugar, and abnormal blood lipids. Table 8.3 summarizes the recommendations from the United States and other countries for the screenings that are the focus of this chapter. A grade of A indicates that there is high certainty of
