An audit of oral glucose tolerance tests at a large teaching hospital: indications, outcomes and confounding factors

This version was published on 1 September 2009

Ann Clin Biochem 2009;46:390-393
© 2009 Association for Clinical Biochemistry


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Original Articles

Joshua Ryan1,
Deepani Siriwardhana2 and
Samuel D Vasikaran3

1 Pacific Laboratory Medicine Services (PaLMS), Royal North Shore Hospital, St Leonards, NSW 2065, Australia;
2 Department of Pathology, Faculty of Medicine, University of Ruhuna, Galle, Sri Lanka;
3 PathWest-Royal Perth Hospital, School of Pathology and Laboratory Medicine, University of Western Australia, Australia

Corresponding author: Samuel D Vasikaran, Department of Core Clinical Pathology and Biochemistry, Royal Perth Hospital, Box X2213 GPO, Perth, WA 6847, Australia. Email: Samuel.vasikaran{at}

Background: Australian guidelines on the diagnosis of diabetes mellitus(DM) recommend performing an oral glucose tolerance test (OGTT)in people with fasting plasma glucose (FPG) values of 5.5–6.9mmol/L.

Aim: To evaluate indications, outcomes and confounding factors ofOGTTs performed at a large teaching hospital and to comparethem with Australian DM guidelines.

Method: A retrospective audit of OGTTs performed over an 18-month periodin a teaching hospital in a major Australian city. Informationgathered included co-morbidities; medications; risk factorsfor type 2 DM; indication for OGTT; results of OGTT and previousglucose tests.

Results: All 129 OGTTs identified were included in the audit. Eighty-nine(69%) were male, with a median age of 57 years (range 19–86),and 3% were of Australian Aboriginal ethnicity. An indicationfor OGTT was identified in 93%, including FPG 5.5–6.9mmol/L (36%) and random plasma glucose (RPG) 5.5–11.0mmol/L (19%). Other indications for OGTT identified includedpolycystic ovary syndrome or metabolic syndrome (8%), peripheralneuropathy (3%) and as part of a research protocol (12%). Forty-two(35%) were inpatients at the time of OGTT, of which 35 (30%)were admitted for acute medical or surgical illnesses such asstroke. Nineteen percent were taking medications known to affectplasma glucose (e.g. oral corticosteroids).

Conclusion: Only 55% of OGTTs had a previous FPG or RPG value warrantingOGTT using current Australian DM guidelines. Other valid indicationsfor OGTT were identified in the majority of the remainder. Inaddition, 41% were performed in the presence of confoundingfactors (such as acute illness or medications known to affectplasma glucose). Many of the OGTTs that are currently beingperformed are in the presence of confounding factors that couldcause misleading results.

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