Diagnosis is usually made on clinical grounds, with a consistent history supported by dietetic assessment. In the presence of a normal clinical exam, with normal neurodevelopmental assessment and normal anthropometric measurements, no diagnostic test is routinely advised. In the presence of failure to thrive, more extensive testing is required (beyond the scope of this review).
Prenatal history should be reviewed, checking for results of the prenatal ultrasound scan and signs of possible neuromuscular problems (polyhydramnios, decreased fetal movements, or arthrogryposis, a rare disorder of joint contractures). Intrauterine growth retardation increases the risk of subsequent feeding disorders, and the birth weight, subsequent weight gain, and measurements of linear growth (length and head circumference) should be reviewed carefully.
Around 50% of children referred with severe feeding disorders are under 1 year of age, and most older children have symptoms extending back to this period.  Further historic diagnostic factors such as age <1 year, prematurity, developmental delay, anatomic abnormalities of the oropharynx, and postsurgical correction of oropharyngeal or GI abnormalities should be sought.
Prematurity increases the risk of feeding disorders, and increases the likelihood of medical manipulation of the oropharynx (ventilation with endotracheal tube placement, tube feeds, oropharyngeal suctioning). One-third of patients referred with feeding disorders are born at <37 weeks' gestation.  The more premature the infant, the more likely there are to be feeding problems. In one feeding disorders program, the prevalence of neonates born at <34 weeks' gestation was 20 times greater than in the local population.  Perinatal events such as time taken to pass meconium, and initial feeding regimen (type of milk, duration of feeding, feeding interval) should be elicited as well.
Evidence of previous illnesses and hospitalizations should be sought. Concurrent illness may impact on an infant's ability to feed (e.g., poor respiratory reserve in patients with congenital heart disease or chronic lung disease). Problems with feeding may also be the presenting complaint of more complex conditions such as cerebral palsy, which become apparent only as the infant matures. Regular hospital attendance can also be evidence of stress and inadequate coping mechanisms within a family, which can result from or lead to difficulties with feeding.
Surgical history, to include correction of oropharyngeal and GI tract abnormalities, GI tract resection, and stoma formation, should be elicited. Disruption of the normal gastroesophageal junction can lead to GERD, as seen, for example, following surgical correction of hiatus hernia or esophageal atresia. Long-term complications of esophageal atresia repair can also include strictures and dysphagia.  Short bowel syndrome after bowel resection was found in 1.1% of a cohort of extremely low birth weight infants treated for necrotizing enterocolitis. 
Family history of atopy or feeding problems should be sought. A familial pattern is seen in pyloric stenosis and in celiac disease.  Atopic families, particularly those with cows' milk protein intolerance (CMPI), are more likely to have children affected with conditions such as CMPI and eosinophilic esophagitis. 
Simple feeding disorders do not exhibit failure to thrive initially. It is important to review growth from birth and relate this to any changes in feeding. For example, in celiac disease there may be failure to gain weight following weaning. Failure to thrive despite adequate caloric intake requires more extensive investigation, which is beyond the scope of this review.
Feeding history and observation of feed
A detailed feeding history should be sought, ideally with the help of a pediatric dietitian. The diet since birth, amount of feed (looking for excessive or inadequate intake, errors in the preparation of formula feeds), types of feed (including changes in formula, and introduction of solids), feeding interval, and time taken to feed should be ascertained. Age at weaning and amount of solids taken during a day should be ascertained in older infants, because decreased solid intake has been associated with failure to thrive in this group. 
It is important to obtain a careful history of simple regurgitation and of vomiting (timing in relation to feeds, volume, forcefulness, presence of bile), abdominal pain, distension or colic, respiratory problems (chronic cough, recurrent wheeze, stridor), posture changes during feeds (arching the neck, turning the head to one side, facial grimacing), and evidence of atopy (skin rashes, rhinitis, diarrhea, and constipation). Where breastfeeding is the exclusive mode of feeding, details about latching on, awareness of milk supply, time spent feeding, and nipple pain should be elicited.
Regurgitation is reported in 67% of normal infants under 4 months of age,   and accounts for 6.1% of pediatric consultations.  Simple regurgitation without any other symptoms is physiologic and does not require either investigation or treatment.   However, many caregivers consider it to be abnormal, and 24% will raise it as a concern at a well-baby visit.   Caregivers are more likely to be concerned when regurgitation happens more than once daily, is a large volume, or is associated with irritability. 
Recurrent vomiting in the absence of failure to thrive and in the presence of a normal physical exam is common in uncomplicated GERD.  Vomiting associated with abdominal pain, colic, and constipation may be seen in both GERD and CMPI. Bilious vomiting in a term infant indicates an upper GI obstruction usually requiring surgical intervention. However, this is a common finding during the establishment of enteral feeding in premature neonates, and is normally managed medically in this population. Projectile, nonbilious vomiting is characteristic of gastric outflow obstruction (e.g., pyloric stenosis). A sudden onset of vomiting in a previously well child may be a symptom of other conditions, notably infections such as meningitis and UTI, which should be considered and ruled out first.
Colic is defined as paroxysms of irritability or crying lasting >3 hours per day and occurring >3 days per week.  Colic can be seen commonly in both GERD and CMPI. Infants who are reported to have symptoms of colic have more disorganized feeding behaviors, less rhythmic sucking, and lower responsiveness during feeds.  Infants with colic are commonly found also to have GERD. 
Coughing or retching at meal times may indicate difficulties with swallowing and possible aspiration.  Chronic aspiration can lead to recurrent pneumonia, even in the absence of these symptoms; this is particularly the case if the infant is neurologically impaired.    Recurrent croup, stridor, or hoarseness of cry can be associated with acid reflux.  Symptoms of GERD are common in infants with recurrent wheeze, and treatment of acid reflux has been shown to decrease wheezing episodes and bronchodilator use in older children with asthma. 
Feeding should be observed for a full 20 minutes to gain an accurate impression of the infant's feeding pattern.  The interactions between the caregiver and the infant should be observed, looking for positive interactions (maintaining eye contact, offering praise for good behaviors, reciprocal vocalization, responding to satiety cues) and negative interactions (forced feeding, bribing, distracting). 
Behavioral and social issues
Social history, to include any stresses within the family, depression, and coping mechanisms, will be helpful both in making the initial diagnosis and in optimizing its management. One large UK study found no association between failure to thrive and either social class or parental education. 
Diagnosis is primarily obtained from the history (food aversion, food refusal, stressful mealtimes). A feed diary documenting these symptoms may be extremely useful in the initial assessment of an infant with a feeding disorder.
An observed feed over 20 minutes to assess caregiver-infant interactions supports the diagnosis. Positive interactions include positive reinforcement for accepting food, good eye contact, and praise. Negative interactions include attempting to force the infant to feed, coaxing the infant, or using distraction techniques during mealtimes.   Overall responsiveness and temperament of the infant should be assessed as well.  Normal infants can cry up to an average of 2 hours per day, and the feed diary may be helpful to determine the length of irritability and any temporal association with feeds. 
Careful measurements of weight, length, and head circumference should be plotted on appropriate charts and compared with growth from birth. The infant should be observed feeding over 20 minutes to assess infant-caregiver interactions and response to cues, level of infant alertness, breathe-suck-swallow coordination, and quality of feed (length, quantity, associated symptoms). A thorough exam to exclude concurrent chronic illness and signs of congenital syndromes is required. A complete neurodevelopmental assessment is essential in the initial assessment of an infant with a feeding disorder.
The symmetry of the infant's face and jaw, lips and palate, and the rhythm and strength of non-nutritive and feeding suck should be assessed to rule out craniofacial abnormalities such as Pierre Robin sequence.  An open-mouthed posture may reflect nasal or pharyngeal obstruction.  Tonsillar hypertrophy should be considered if mouth breathing or stertorous (snoring) breathing is heard.  The presence of ankyloglossia (tongue-tie) may explain difficulties with breastfeeding.   
Neurodevelopmental assessment is of particular importance. Feeding disorders are seen in up to 80% of children with neurodevelopmental delay.  Failure to achieve feeding milestones may be the presenting sign of more global developmental delay. Attention should be paid to the infant's posture, position during feeds, truncal tone, and movement. Drooling may be a sign of difficulty swallowing. The infant's response to sensory stimuli may also give more clues about developmental issues. 
Increased respiratory rate and increased work of breathing at rest will impair ability to feed.  Poor coordination, weak suck, and short sucking bursts are described in infants with severe bronchopulmonary dysplasia.  Apnea and bradycardia with feeds may reflect either a central problem with breathe-suck-swallow coordination, or may reflect GERD. 
Simple overfeeding can be ascertained by taking a careful feeding history from the caregivers and does not require tests.
GERD is usually a clinical diagnosis in this age group, though symptoms are nonspecific and unreliable.  Upper GI contrast, pH study, or impedance monitoring may be considered when there is poor weight gain, after exclusion of causes of failure to thrive.  Before undertaking surgery to manage severe GERD, most surgeons will require the diagnosis to be confirmed with a pH study, and other anatomic abnormalities to be excluded with an upper GI contrast study.
Nuclear scintigraphy shows both acid and nonacid reflux, as well as giving information about gastric emptying (which may be delayed in GERD). However, the absence of age-specific normative data limits its use in infants and small children. 
GERD may be associated with aspiration, particularly if the patient has associated neurologic or neuromuscular problems. CXR and upper GI contrast studies can be used to diagnose aspiration. If these are not conclusive, bronchoscopy or nuclear scintigraphy may be helpful.
Anatomic abnormalities requiring surgical intervention
These should be considered if craniofacial abnormalities are detected on exam, or if there is a history of drooling or choking, or recurrent pulmonary infections (consider a possible aspiration or a tracheoesophageal fistula). Suspected aspiration can be diagnosed on CXR and upper GI contrast study.  Bronchoscopy with fat-laden alveolar macrophages found on lavage can support a diagnosis of aspiration, but is usually reserved for patients in whom the diagnosis is in doubt and upper GI study is negative. 
Bilious vomiting or projectile vomiting suggests upper GI obstruction, which should be investigated by abdominal x-ray, abdominal ultrasound, or CT following discussion with surgical colleagues. CT scan may be requested by surgeons; however, it is not a routine test used to diagnose feeding disorders.
Neurologic or neuromuscular disorders predisposing to feeding disorders
The diagnosis of neurologic or neuromuscular disorder is usually made on the basis of an abnormal neurologic exam, with a supporting family history or perinatal history. Initial assessment should be made with the assistance of specialized speech and language therapists and dietitians, and may involve upper GI contrast studies and videofluoroscopy to assess swallow. Fiberoptic endoscopic evaluation of swallowing with sensory testing (FESST) may be useful to determine swallowing function, particularly events around the pharyngeal part of swallowing, but does not provide visualization of the oral phase of swallowing, because the endoscope is passed transnasally.   FESST is radiation-free and is generally well tolerated, and can be repeated if needed. It is a highly specialized test, usually available only in tertiary centers.
In children with cerebral palsy, a wide range of feeding problems have been described, including GERD (56%), dysphagia (27%), and aversive feeding behaviors (18%).  Diagnosis of GERD is clinical and may respond to a trial of acid suppression. However, progression to esophageal pH study, upper GI contrast study, and scintigraphy is recommended if symptoms are severe, because some of these infants will go on to require gastrostomy insertion and possibly fundoplication.   Infants with neurologic impairment and GERD are particularly at risk of episodes of silent aspiration, and CXR and bronchoscopy should be considered.   
Cows' milk protein intolerance (CMPI)
Diagnosis of CMPI may be made on clinical grounds with a strong family history and supporting symptoms such as rash or rhinitis. A RAST assay (radio-allergosorbent testing) specific to cows' milk protein may support the diagnosis of CMPI, but it is often simpler to give a trial of hypoallergenic feed, as symptoms usually improve dramatically within a few days if this is the correct diagnosis.   If symptoms fail to improve with dietary modification, the original diagnosis should be reconsidered.
May be diagnosed on history (watery stool, abdominal distension, and flatulence) and is usually diagnosed by performing a therapeutic trial of lactose-free feeds. A fresh stool sample would also be positive for fecal-reducing substances. Hypoallergenic formula preparations are available that are suitable for use in infants with either lactose or cows' milk intolerance, which is helpful given the overlap of symptoms in these disorders.
Secondary lactose intolerance is usually a transient complication of a viral infection of the GI tract, and a short-term trial of a soy-based or hypoallergenic formula is sufficient until symptoms abate.
May be suspected with a positive family history and failure to gain weight after the start of weaning. Symptomatic infants should be screened with tissue transglutaminase assay (TTG) and referred for intestinal biopsy if positive. Antiendomysial and antigliadin assays are no longer routinely recommended. 
Other specialized investigations
Other tests such as genetics assessment or echocardiography will be determined by the suspected clinical syndrome (beyond the scope of this review). Many patients with complex needs, such as infants with cleft lip and palate, will have been under the review of multidisciplinary teams since birth.