In a child with global developmental delay, the SINGLE most important first-line investigation to identify a potentially treatable cause is:

• A MRI brain
• B Chromosomal microarray (CMA)
• C Thyroid function tests (TSH, fT4) ✓
• D Urine organic acids and plasma amino acids (metabolic screen)

Explanation

Hypothyroidism is the single most common and most easily treatable cause of global developmental delay and intellectual disability that can be identified by a simple blood test (TSH and fT4). Congenital hypothyroidism, if missed on newborn screening or not screened, causes irreversible intellectual disability, but treatment with L-thyroxine dramatically reverses developmental delay if started early. While CMA and MRI are higher yield for aetiology overall, and metabolic screens identify rare treatable IEM, TSH/fT4 is the most important immediate investigation due to its prevalence, treatability, and simplicity. Many guidelines recommend thyroid function as the first targeted investigation.

Reference: Ghai Essential Pediatrics, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.