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The ‘speed bump sign’ is a clinical symptom characterised by aggravated abdominal pain while driving over speed bumps. The speed bump sign is a useful ‘rule-out’ test for diagnosing acute appendicitis. With good accessibility, the speed bump sign may be added as a routine part of taking the history of patients with abdominal pain.
The speed bump sign provided an easy indicator in predicting AA upon the arrival of a patient with abdominal pain at an emergency room. The diagnostic odds ratio (DOR) ratio is a single indicator of how informative a diagnostic test is that is independent of the prevalence of the disease/disorder [11]. Higher DOR may be indicative of better test performance. In the past studies, pooled DORs of various indicators for AA diagnosis have been reported, such as Alvarado score (7.99) [12], Raja Isteri Pengiran Anak Saleha Appendicitis (RIPASA) score (24.66) [12], neutrophil-to-lymphocyte ratio (14.34) [13], procalcitonin (21.4) [14], abdominal ultrasound (6.88) [15], CT (129.6) [8] and MRI (129.6) [8]. CT and MRI are without doubts the most accuracy tool for AA diagnosis.
If a test displays a high sensitivity, it will detect the disease or disorder with confidence; if the results of the test are negative, there is certainty that no disease or disorder is present. Therefore, a high sensitivity test helps to rule out the disease/disorder when the result is negative, which is called the mnemonics of SnNout [16]. On the other hand, the mnemonics of SpPin indicates that a high specificity test helps rule-in a disease/disorder with a high degree of confidence if the result is positive. Based on the pooled estimates, the high sensitivity of increasing pain while driving over speed bumps is a basis for yielding a strong rule-out value to exclude AA. Since 1980, many score systems have been developed for the diagnosis of appendicitis, and the most widely used system is Alvarado score. This system, including eight parameters with clinical symptoms and laboratory data (migration of pain, anorexia, nausea, tenderness over right lower quadrant, rebounding pain, elevated body temperature, leukocytosis and shift of white blood cell count to the left) is considered a reasonable and simple system that can be used easily in clinics or emergency departments [17]. However, the pooled sensitivity of the Alvarado score for the diagnosis of appendicitis is only 69% (95% CI = 67–71%) in a recent meta-analysis [12]. Another system is Raja Isteri Pengiran Anak Saleha Appendicitis (RIPASA) score, which consists of two demographic information (gender and age), five symptoms (right iliac fossa pain, migration of right lower quadrant pain, anorexia, nausea and vomiting and duration of symptoms), five signs (right iliac fossa tenderness, right iliac fossa guarding, rebound tenderness, Rovsing’s sign and elevated body temperature) and two laboratory data (raised white blood cell count and negative urine analysis); it has been considered the most accurate scoring system for AA diagnosis [18]. The pooled sensitivity of the speed bump sign is similar to RIPASA score (94%, 95% CI = 92–95%) [12], indicating the value of the speed bump sign in clinical applications. In addition, unnecessary CT scans can be avoided because of the similar pooled sensitivity between speed bump sign and CT (95%, 95% CI = 93–96%) [19]; consequently, medical cost and radiation exposure can be reduced.
The low specificity (49%) of the speed bump sign indicates that patients do not definitely have AA, although they experience aggravating pain when they pass speed bumps during travel. In fact, the specificity of RIPASA score is also low (55%, 95% CI = 51–59%) [18]. Further examination with high specificity in a case with a positive speed bump sign should be performed.
Speed pump sign can be a good tool for AA screening in the triage of emergency medical services. However, applying likelihood ratios [LR (+) and LR (−)] for clinical judgement may be more useful in daily practice [20]. LR represents how much more likely a diagnostic tool is amongst people who have specific clinical presentation than amongst people who do not have the presentation [20]. The pretest probability of an individual case may rely on a physician’s subjective experience and objective information, such as physical examinations, laboratory tests and image findings. Weighted judgement, or posttest probability in statistics, can be changed following the consideration of LR. Indeed, the results demonstrated that the negative finding of the speed bump sign in a patient with abdominal pain can be applied as a strong hint to exclude the diagnosis of AA. However, probabilities of 28% are still not good enough when the pretest probability is as high as 75% with negative speed sign. Combining with the Raja Isteri Pengiran Anak Saleha Appendicitis (RIPASA) score and speed bump sign may provide higher sensitivity for AA diagnosis. Procalcitonin, an indicator for systemic bacterial infection, provided better pooled specificity than sensitivity for AA diagnosis [14]. Therefore, a new scoring system including both speed bump sign and procalcitonin might be more helpful. Such evidence should be confirmed by future research.
The low specificity (49%) of the speed bump sign indicates that patients do not definitely have AA, although they experience aggravating pain when they pass speed bumps during travel.