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We read with great interest the recent publication by Lin et al,1 which reported diarrhoea as the most common GI symptom in patients with COVID-19. Diarrhoea as a symptom of COVID-19 has been commonly observed,2 3 but the cause remains unknown.
Diarrhoea occurs from excessive production of serotonin (5-hydroxytryptamine, 5-HT) in the GI tract.4 Ninety-five per cent of 5-HT is produced and released from the enterochromaffin cells within the epithelium of the GI tract. 5-HT localised to the GI tract is a key modulator of GI peristalsis.5 We hypothesised that plasma 5-HT levels are increased in patients with COVID-19 with diarrhoea.
Table 1 summarises the COVID-19 severity, interleukin 6 (IL-6), IgM/IgG antibodies, fever, GI symptoms, plasma 5-HT, 5-hydroxyindoleacetic acid (5-HIAA), underlying diabetes, body mass index, gender and age measured in 80 patients with COVID-19 (10 patients with diarrhoea) and 18 healthy donors (see online supplemental material). Correlation analysis identified 5-HT, 5-HIAA and IL-6 as the most noticeable features in the COVID-19 cohort with diarrhoea. Patients with COVID-19 had significantly increased plasma 5-HT and 5-HIAA levels compared with healthy donors (figure 1A,D). When patients were categorised by disease severity, 5-HT and 5-HIAA levels increased with higher severity of symptoms (figure 1B,E). Patients with COVID-19 with diarrhoea had substantially higher 5-HT and 5-HIAA levels compared with patients without diarrhoea and the healthy group (table 1 and …
SH and BJ contributed equally.
Contributors SH, BJ and SR designed the research. SH, BJ and SR analysed and generated the data. PP, SM, VG, FML, AG-B and AH obtained and analysed COVID-19 and healthy donor blood samples and clinical data. SH, BJ, BC and SR wrote the paper. SR revised the paper. All authors have approved the final version of the manuscript.
Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.
Competing interests None declared.
Provenance and peer review Not commissioned; internally peer reviewed.
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