Download Describe the potential causes for,and appropriate clinical chemistry

Describe the potential causes for, and appropriate clinical chemistry investigations
of an infant presenting with failure to thrive.
Failure to thrive (FTT) is defined as a current weight or rate of weight gain significantly
below that expected for children of similar age and sex. It usually refers to growth below
the 3rd or 5th percentiles or a change in growth rate that has crossed two major percentiles
in a short time.
Potential causes of FTT in infants
FTT occurs due to 3 mechanisms or a combination of them. It could be due to failure to
provide enough calories, inability of the body to absorb enough calories or due to
increased energy expenditure. Causes of FTT are divided into organic and non organic
causes. Non organic FTT occurs when no underlying medical condition is found and it is
usually due to psychosocial and/or nutritional deprivation. This could be due to maternal
depression ,child neglect, improper formula preparation, delayed introduction of age
appropriate foods etc. This will lead to a child not getting enough calories to thrive.
Organic FTT occurs when an underlying medical condition causing poor growth is
diagnosed. Common organic causes of FTT in infancy are listed in the table below
Common organic causes of FTT in infancy
MALABSORPTION
Intestinal causes (Food intolerance eg.lactose,
Celiac disease)
Pancreatic insufficiency(cystic fibrosis)
INHERITED METABOLIC DISEASES
CHRONIC DISEASE
Pulmonary
Cardiac
Renal
Liver
ENDOCRINE DISEASE
DM,hypothyroidism,GH deficiency,hyperthyroidism
CHRONIC/RECURRENT INFECTIONS
Eg.immunodeficiency,HIV,recurrent UTI
OTHERS:
Gastroesophageal reflux
Pyloric stenosis
Neurologic disease
Malignancy
Insufficient calories intake may occur due to the above mentioned non organic causes or
could be due to difficulties with feeding as in motor neuron diseases or due to
regurgitation and vomiting which may occur with gastroesophageal reflux disease,
pyloric stenosis or inborn errors of metabolism. Common causes of malabsorption in
infancy are food intolerance, food allergy, celiac disease and cystic fibrosis. Chronic
diseases as well as recurrent infections and inborn errors of metabolism may cause failure
to thrive due to improper energy utilization and energy over expenditure. Endocrine
diseases such as DM, hypothyroidism and hypopituitarism may cause FTT but they are
more common later during childhood.
Clinical chemistry investigations:
Non organic causes of FTT are more common than organic causes especially in
developing countries. Nevertheless, it is considered appropriate to screen infants with
FTT for common organic causes which have to be ruled out before a
psychosocial/nutritional FTT is diagnosed. In addition, proper psychosocial and
nutritional history should be saught.The history and/or physical examination eg.cardiac
murmur may point to a specific cause.
Basic clinical biochemistry investigations plays a major role in identifying patients with
chronic kidney or liver disease/RTA, screening and diagnosis of inborn errors of
metabolism, Identifying few causes of malabsorption mainly cystic fibrosis and celiac
disease.
Basic biochemistry investigations may initially include RFT, LFT to rule out chronic
liver or kidney disease. Raised liver enzymes may be due to many causes including
inborn errors of metabolism as well as chronic infections and malignancies. Isolated rise
of ALP without evidence of liver disease may point to vitamin D deficiency.
Low albumin may point to malnutrition/malabsorption but it could be low in chronic
disease as well as in kidney disease with proteinuria. Moreover, it has a half life of 21
days and needs weeks to go down in cases of malnutrition or liver disease.Doing serum
prealbumin is found to be a better indicator of malnutrition since it has a half life of 2
days and if it fails to increase after a trial of feeding then further investigations to rule out
other causes is appropriate. CRP should be done along with prealbumin to rule out
inflammation as a cause of low prealbuminas. Doing other markers of malnutrition at this
stage is appropriate. These include serum calcium, magnesium, ferritin, folic acid and
vitamin B12. In addition, performing Urinalysis for protein, bilirubin, reducing
substances and PH helps screen for nephropathy and some inborn errors of metabolism.
Additional biochemistry tests may be done as indicated from the history and examination.
1.patients presenting with chronic diarrhea (or steatorrhoea), flatulence or abdominal
pain, a stool sample may be taken for reducing substances(for lactose intolerance) and pH
measurement.It may be analyzed for elastase if pancreatic insufficiency due to cystic
fibrosis is suspected. If cystic fibrosis is suspected then a chloride sweat test is
performed.
Celiac disease is not uncommon to present in this age group so endomysial antibodies or
transglutaminase antibodies should be done to screen for celiac disease.Those tests have
been shown to be very sensitive in diagnosing celiac disease. Serum IgA should be done
in patients with chronic diarrhea/ recurrent GIT infections.
2.Screening for inborn errors of metabolism is done for Patients with abnormal LFTS,
non specific symptoms, hypoglycemia or suspected metabolic disorder. Serum ammonia
and lactate along with blood gas analysis are first line investigations. Further metabolic
workup including plasma and urine amino acids/organic acids is done accordingly.
3. Immunoglobulins are done in patients with recurrent infections. They could be low in
malnutrition.
4. Endocrine causes are uncommon to present with FTT at this age group especially that
neonatal screening for hypothyroidism has been established. Nevertheless, TFT should be
done if thyroid disease is suspected .
Finally, in addition to clinical biochemistry investigations it is worth mentioning other
complementary tests from other labs eg. FBC, urine and stool cultures for diagnosing gut
infestations,genetic testing for CF, gastroesophageoscopy and sigmoidoscopy with biopsy
to diagnose intestinal causes of malabsorption ect.
Conclusion:
FTT in an infant is commonly due to non organic causes. Thorough nutritional and
psychosocial history along with physical examination is important to guide management
but basic clinical chemistry investigations may help rule out and follow up treatment of
common organic causes (mainly metabolic diseases, cystic fibrosis, celiac disease,
biochemical consequences of malnutrition) and guide further management. It may help
screen for malabsorption but further evaluation by endoscopic means and biopsy facilities
is more appropriate.