Table 5 Diagnostic yield of tests in children with global developmental delay

TestDiagnostic yield, %
Based on data from studies listed in table 4,
* tables 2 and 3,
† and table 1.‡
‡ Metabolic testing usually consists of urine organic acids, serum amino acids, serum lactate, ammonia level, and a capillary blood gas.
TSH = thyroid stimulating hormone; T4 = thyroxine; UNS = universal newborn screening.
Neuroimaging*
    MRI scan, nonenhanced55.3
    CT scan39.0
Genetic studies
    Routine cytogenetic  studies3.7
    Subtelomeric deletion6.6
    Fragile X screen2.6
    MECP2Unknown
Metabolic testing≈1
Thyroid screen (serum TSH, T4)Near 0 if UNS; ≈4 if no UNS
Serum lead levelUnknown
EEG (routine)≈1