To the Editor: The 50 g glucose challenge test (GCT) is widely recommended as a screening test for gestational diabetes (GD).1 The test consists of a 50 g oral glucose load given at any time of the day, followed one hour later by the measurement of the plasma glucose concentration.2 This test is recognised as imperfect for screening, as sensitivity and specificity are not 100%.2,3 It is known that glucose tolerance deteriorates in the afternoon,4 which raises the question of whether time of day influences the response to the 50 g GCT.
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- 1. The Expert Committee on the Diagnosis and Classification of Diabetes Mellitus. Report of the Expert Committee on the Diagnosis and Classification of Diabetes Mellitus. Diabetes Care 1997; 20: 1183-1197.
- 2. American Diabetes Association. Gestational diabetes mellitus. Diabetes Care 2001; 24 Suppl 1: S77-S79.
- 3. McElduff A, Goldring J, Gordon P, Wyndham L. A direct comparison of the measurement of a random plasma glucose and a post-50g glucose load glucose in the detection of gestational diabetes. Aust N Z J Obstet Gynaecol 1994; 34: 28-30.
- 4. Campbell IT, Jarrett RJ, Keen H. Diurnal and seasonal variation in oral glucose tolerance. Studies in the Antarctic. Diabetologia 1975; 11: 139-145.
- 5. Hoffman L, Nolan C, Wilson JD, et al. Gestational diabetes — management guidelines. The Australasian Diabetes in Pregnancy Society. Med J Aust 1998; 169: 93-97.