GH1 and isolated congenital growth hormone deficiency: Although two thirds of patients with history of IGHD (36/54 [67%]; value missing for 1 patient) had subnormal serum IGF-I (<-2.0 SDS) at retesting, this threshold did not discriminate well between those who retested with peak GH above (n = 35) or below (n = 20) 5 μg/L (specificity 50%; Table 3).