Chronic abdominal pain; what investigations should you do?

What is the value of sending off a full blood count, C- reactive protein (CRP) and erythrocyte sedimentation rate (ESR) in a child who has chronic abdominal pain? Zeevenhooven J et al [J Pediatr 2020;219:76-82e. https://doi.org/10.1016/j.jpeds.2019.12.017] have investigated the additional value of blood parameters (haemoglobin, C-reactive protein, erythrocyte sedimentation rate) to serum anti-tissue transglutaminase (anti-tTG), faecal calprotectin, and Giardia lamblia when investigating a child with chronic abdominal pain. In a retrospective cohort study of 853 children aged 4–18 years with abdominal pain for greater than 2 months, there were 102 (12%) of patients who had an organic disorder. They compared two strategies: strategy 1 (faecal calprotectin, anti-tTG, G lamblia, and blood parameters) to strategy 2 (faecal calprotectin, anti-tTG, G lamblia) They described six red flag/alarm symptoms. In the presence of one or more alarm symptoms, the sensitivity of strategies 1 and 2 was 92% (95% CI, 83 to 96) and 92% (95% CI, 83 to 96), and the areas under the curve were 0.93 (95% CI, 0.89 to 0.98) and 0.90 (95% CI, 0.84 to 0.97) (p=ns). So to distinguish between a functional and an organic cause for chronic abdominal pain, their conclusion was that the haemoglobin, CRP, …