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Evaluation of weight loss in infants six months of age and younger

Derya Caglar, MD
Section Editor
George A Woodward, MD
Deputy Editor
James F Wiley, II, MD, MPH


This topic will discuss the approach to weight loss in the infant who is six months of age and younger. The evaluation of weight loss in older infants, children, adolescents, and adults is discussed separately. (See "Evaluation of weight loss in infants over six months of age, children, and adolescents" and "Approach to the patient with unintentional weight loss".)


Weight loss in young infants is commonly caused by acute infection, problems with feeding, milk protein allergy, malnutrition, or failure to thrive. Gastroesophageal reflux disease, pyloric stenosis, and child neglect are other frequent etiologies. Dehydration associated with any etiology can be severe. Although less common, other life-threatening conditions include intestinal malrotation with volvulus, congenital heart disease, congenital adrenal hyperplasia, and inborn errors of metabolism. A careful, thorough history and physical examination, in conjunction with the judicious use of laboratory tests, will often reveal the cause.


The major components of weight include water, protein, carbohydrates, and fats. Weight loss occurs when the daily balance of one or several of these components becomes negative. During infancy and early childhood, major causes of weight loss include inadequate calorie intake to meets the energy demands of the child's metabolism for daily activity and growth, or negative fluid balance. Specific etiologies include decreased calorie intake, normal calorie intake with an increased metabolic need, or normal calorie intake in the setting of malabsorption or excessive loss. During acute illnesses, such as gastroenteritis, fluid losses that exceed intake can lead to significant weight loss.


The differential diagnosis for weight loss in the young infant is wide and may require an extensive work-up (table 1). In many patients, a diagnosis is not established during an initial visit, but the evaluation may begin and specialist referrals made as needed.

Life-threatening conditions

Dehydration — Severe dehydration from acute gastroenteritis can lead to significant weight loss from fluid losses. Dehydration from gastroenteritis is one of the leading causes of death among infants in developing nations. Infants with acute gastroenteritis typically present with acute onset of diarrhea, vomiting, fever, and decreased feeding. Blood or mucous in the stool or rice water stool suggest bacterial enteritis or cholera, respectively. Dehydration may also occur due to other acute infections (eg, pneumonia, sepsis, urinary tract infection), conditions causing decreased intake (eg, feeding disorders, congenital heart disease, child neglect, malnutrition) or conditions associated with increased loses (eg, gastroesophageal reflux disease, pyloric stenosis, milk protein allergy with diarrhea, or intestinal malabsorption). Findings of significant dehydration (eg, prolonged capillary refill, dry mucous membranes, sunken eyes or fontanelle, or lethargy) are commonly found on physical examination. (See "Clinical assessment and diagnosis of hypovolemia (dehydration) in children", section on 'Clinical assessment'.)

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Literature review current through: Dec 2017. | This topic last updated: Mar 23, 2017.
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