Lactose malabsorption, which is uncommon in Scandinavia and North-western Europe (3–8%) but close to 100% in most of South-east Asia, 1 has been proposed as a cause of recurrent abdominal pain in children. 2,3 Some studies support this proposal, 4 while others suggest that it is not an important cause. 5 The reason why lactose malabsorption should cause abdominal pain is unclear, but it may be related to increased sensitivity to gaseous distension of the gastrointestinal tract. Measurement of breath hydrogen is an efficient screening test for lactase deficiency in children and adults with suspected lactose intolerance. It is a sensitive and specific test, it is non- invasive and it is not affected by gastric emptying or metabolic factors. 6 The test has been used by many researchers to examine the relationship between recurrent abdominal pain and lactose intolerance due to lactase deficiency. The aim of the present study was to determine the preva- lence of lactase deficiency among 24 Malaysian children with recurrent abdominal pain fulfilling Apley’s criteria 7,8 and to describe their clinical characteristics. METHODS Twenty-four children referred consecutively to the University of Malaya Medical Centre between January 1999 and December 1999 who fulfilled Apley’s criteria 7,8 (at least three episodes of abdominal pain severe enough to affect normal activity over a period longer than 3 months) were included in the study. Each patient was tested for lactase deficiency using a pocket breath test analyser (BreatH2 meter; Europa Scientific, Cheshire, England). The BreatH2 meter is based on an electro- lytic fuel cell that works through the reaction of hydrogen with an electrolyte at one electrode and oxygen (from ambient air) at the other. An electrical current proportional to hydrogen concentration is generated by this reaction. A microprocessor senses the output from the fuel cell, detecting peak concentra- tions of expired air and showing the result in parts per million (p.p.m.). The clinical application of such a device has been compared with the standard GMI-exhaled monitor and the correlation of both methods during clinical application was found to be excellent (y = 1.08x + 0.96; r = 0.959). 9 Each patient was fasted overnight and, the following morning, baseline breath hydrogen was measured. The patient was then given 2 g/kg lactose orally (10% lactose solution) up to a maximum of 20 g, which represents a drink of approxi- mately 500 mL milk. Breath hydrogen was measured immedi- ately after ingestion of lactose and then every 30 min for 2.5 h. A rise in breath hydrogen of over 20 p.p.m. was regarded as a positive result. If the result was negative, the patient was given J. Paediatr. Child Health (2001) 37, 157–160 Lactase deficiency among Malaysian children with recurrent abdominal pain CCM BOEY Department of Paediatrics, University of Malaya Medical Centre, Kuala Lumpur,Malaysia Objectives: To determine the prevalence of lactase deficiency among Malaysian children with recurrent abdominal pain and to describe their clinical characteristics. Methodology: Twenty-four children referred consecutively to the University of Malaya Medical Centre who fulfilled Apley’s criteria (at least three episodes of abdominal pain severe enough to affect normal activity over a period longer than 3 months) were tested for lactase deficiency using a pocket breath test analyser (BreatH2 meter; Europa Scientific, Cheshire, England). Lactulose was used to check for hydrogen-producing capacity. Results: There were 14 males and 10 females in the study, consisting of five Malays, 14 Chinese and five Indians. Mean age was 9.9 years. Seventeen of the 24 children (70.8%) with recurrent abdominal pain who underwent the breath hydrogen test had a positive result. In those with a negative result, subsequent lactulose administration resulted in a positive rise in breath hydrogen. None of the 24 children developed abdominal pain during the test. All the Indian subjects, 71.4% of the Chinese subjects and 40% of the Malay subjects with recurrent abdominal pain had lactase deficiency. The proportion of boys and girls with lactase deficiency was similar (71.4 vs 70.0%, respectively). There was no significant difference between lactase sufficient and deficient children with recurrent abdominal pain with regard to sex, age, ethnic group and clinical features. Following a lactose-free diet, none of the children in the breath hydrogen positive and negative groups reported any appreciable difference in pain symptoms. Conclusions: The prevalence of lactase deficiency among this group of Malaysian children with recurrent abdominal pain was high, but lactase deficiency did not appear to play an important role in causing the symptoms. Key words: lactase deficiency; lactase sufficiency; recurrent abdominal pain. Correspondence: Dr CCM Boey, Department of Paediatrics, University of Malaya Medical Centre, 59100 Kuala Lumpur, Malaysia. Email: boeycm@medicine.med.um.edu.my Accepted for publication 30 August 2000.