Failure to Thrive (FTT) is not just for the clinics. We need to be on the lookout, because if we find it, there is already a big problem.
Definitions of Failure to Thrive may quibble on the details, but for us in the ED:
We can get around the longitudinal requirement by looking at weight as a "spot check" -- if grossly below weight without any other chronic condition, be alarmed.
Failure to thrive results from inadequate calories. This may be due to:
Any concern should trigger a more complete H&P (in audio).
Classic instructional video on the mother-infant dyad (scan through for various types).
After a focused H&P, you may need to admit the child for further workup, or to show that he can/cannot gain weight with routine care.
Remember, if you are the first one to bring this up, there is a real problem. By definition, an outpatient plan has failed. We will not be able to distinguish among the various possibilities of organic and non-organic causes (or mix thereof); our job is to be ready to catch it and act on it. The child's development, future intelligence, and welfare are at risk.
Jaffe AC. Failure to Thrive. Pediatrics in Review. 2011; 32(3)
Prutsky GJ et al. When Developmental Delay and Failure to Thrive Are Not Psychosocial. Hospital Pediatrics. 2016; (1):6