Abstract
Introduction: Diagnosing GH deficiency (GHD) is a challenge and depends on GH response to GH stimulatory test (GHST), whose cutoff remains unclear.
Aims: To identify GH peak cutoff which best diagnoses GHD in short stature (SS) patients.
Methods: Retrospective study: 858 children (0-18y) realized 1290 GHST between 2001-2016. Three-hundred-forty patients were classified as isolated SS (ISS = isolated GHD, familial SS, idiopathic SS) or GHD+hypopituitarism (MPHD). In those with known adult height (AH), clinical and biochemical data (median and interquartile range) were compared (Wilcoxon test). ROC curve was used to find discriminating GH peak in the ISS group, considering true GHD those who underwent rhGH treatment, reached AH ≥ -2 SDS and parental corrected adult height (AH – target height *TH+) ≥ -1.6 SDS.
Results: Known AH was found in 146 out of 340. At admission: 10.1yrs [6.1; 12.9]; height (H) = -2.7 SDS [-3.4; -2.1]; H-TH = -1.5 SDS [-2.4; -0.7]; height velocity (HV) = -0.3 SDS [-1,3; 1]; plasma IGF1 = -1.6 SDS [-2.1; -0.9], maximum GH peak = 4.2 ng/mL [0.8; 9.1]. Forty-five patients presented MPHD and 101 presented ISS. MPHD patients had lower IGF1 (-2.1 vs. -1.4 SDS; p = 0.01) and GH peak (0.4 vs. 7 ng/mL; p<0.0001). Sixty-five patients received rhGH until reaching AH (MPHD = 24; ISS = 41). Decision for therapy was based on clinical judgment besides GHST. Treated patients were younger (8 vs 12.1yrs; p = 0.001), had lower HV (-1 vs. 0.1 SDS; p = 0.0001), IGF1 (-1.8 vs. -1.4 SDS; p = 0.02), GH peak (1.6 vs. 6.7 ng/ mL; p = 0.02), achieved higher AH (-1.6 vs. -2.2 SDS; p = 0.03) and AH-TH (-0.2 vs. -0.9; p = 0.02). True GHD was identified in 24 ISS. ROC analysis suggested a 6.8 ng/ml GH peak cutoff for ISS patients (AUC = 0.68, low sensitivity = 75%, specificity = 61% and LR = 1.92).
Conclusions: In ISS patients, the most discriminative GH peak cutoff to identify GHD is 6.8 ng/ml. However, solely, this test has a poor diagnostic performance.
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