Introduction:
Lower gastrointestinal bleeding (LGIB) is not a rare clinical problem in children. The aetiology of LGIB varies according to age. Likewise, experiences in different countries reflect the disparities in the frequency of various causes of LGIB in children. Although some cases can be diagnosed clinically, choosing the appropriate diagnostic methods in children is challenging. The aim of the study was to determine the aetiology of LGIB in children and analyse the diagnostic procedures needed to make a diagnosis.

Material and methods:
The medical records of children with chronic LGIB admitted to the Paediatric Gastroenterology Department were reviewed. The diagnoses and diagnostic procedures were analysed according to age groups (< 5 with subgroups < 2 and 2–5, 5–10, and > 10 years old).

Results:
227 patients were enrolled in the study. The most important causes of LGIB among all patients were constipation associated with anal fissures (36.6%) and inflammatory bowel disease (IBD) (33.5%). According to age groups, the main causes of LGIB were: up to 5 years old – constipation (39.62%) and food allergy (28.3%), in the youngest age subgroup up to 2 years old – food allergy (52.38%), between 5 and 10 years old – constipation (44%) and ulcerative colitis (14%), over 10 years old – IBD ulcerative colitis (36.29%), Crohn’s disease (13.71%), and constipation (32.26%). Patients with IBD were more likely to have anaemia and weight loss. The level of faecal calprotectin was significantly elevated in children with IBD and colorectal polyps.

Conclusions:
Constipation is a common cause of LGIB in all age groups of children. Food allergy should be considered in infants and young children, but it is rarely seen in children over 5 years old. In children older than 5 years old, diagnostics for IBD should be carried out, especially in patients with weight loss, high levels of faecal calprotectin, and anaemia. Colorectal polyps and Meckel’s diverticulum are less common causes of LGIB.