A 14-month-old with faltering growth and diarrhoea
A 14-month-old boy is referred to the general paediatric clinic with diarrhoea and poor weight gain. He was born at term, birth weight 3.4 kg. He was breastfed until 12 months and weaned onto cow's-milk-based formula and then whole cow's milk. For 4 months he has had 4–6 loose, pale, offensive stools per day, intermittent abdominal distension and irritability. His weight is now 8.2 kg (0.4th centile, down from the 25th at 6 months) and length is on the 10th centile. He looks pale. There is no blood in the stool, no fever, no rash and no vomiting. He is alert and interactive. Haemoglobin is 96 g/L with a low mean corpuscular volume; ferritin is low; albumin is 33 g/L; coeliac serology (IgA anti-tTG) is negative, but total IgA is not yet available. Stool microscopy is negative.
1. The total IgA comes back as 0.05 g/L (low). How does this change your plan, and what would you do next?
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A low total IgA means the negative IgA anti-tTG is uninterpretable - selective IgA deficiency is common (about 1 in 500) and causes false-negative IgA-based coeliac serology. Coeliac disease remains firmly on the differential and must be actively excluded.
Next steps:
- Send IgG-based serology - anti-tTG IgG and/or anti-endomysial IgG - and check IgG subclasses if recurrent infections.
- Do not start a gluten-free diet before coeliac testing is complete. If serology is positive, refer for upper GI endoscopy with duodenal biopsies (the gold standard); do not diagnose on serology alone in a child of this age without discussing the no-biopsy pathway criteria with a paediatric gastroenterologist.
- If serology is negative but suspicion remains high, HLA-DQ2/DQ8 testing has high negative predictive value and can help avoid unnecessary biopsy.
- In parallel, because cow's-milk protein allergy is the other leading diagnosis, discuss a 2–4 week trial of an extensively hydrolysed formula (or continued breastfeeding with maternal dairy exclusion) with a planned objective reassessment of stools, weight and irritability. Do not run a gluten-free and a dairy-free trial simultaneously without a clear plan, or you will not know which worked.
- Treat the iron deficiency, arrange dietitian review, and monitor weight and length on the chart.
2. The parents ask for a 'food allergy test' to settle the matter. Explain what testing can and cannot do here.
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What testing can do:
- Specific IgE blood tests or skin-prick tests are useful for IgE-mediated allergy (immediate hives, swelling, wheeze within minutes).
- In non-IgE-mediated cow's-milk protein allergy - which is what this child's chronic diarrhoea suggests - these tests are usually negative and a negative result does not exclude the diagnosis. The diagnosis is clinical, confirmed by an elimination trial and, where appropriate, reintroduction.
What testing cannot do:
- It cannot 'rule out' food allergy in this presentation, and a positive test alone does not prove causation - positive tests are common in children who tolerate the food.
- Broad 'food panel' or IgG food-intolerance testing is not evidence-based and should not be offered; it leads to unnecessary restriction and nutritional harm.
What to say: explain that the diagnosis will be made by a structured elimination and reintroduction trial with dietitian support and growth monitoring, alongside completing the coeliac work-up. Set expectations that improvement takes 2–4 weeks and that reintroduction is needed to confirm the diagnosis and avoid unnecessary long-term restriction.