An audit of oral glucose tolerance tests at a large teaching hospital: indications, outcomes and confounding factors.
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 5.5-6.9 mmol/L.


OBJECTIVE
To evaluate indications, outcomes and confounding factors of OGTTs performed at a large teaching hospital and to compare them with Australian DM guidelines.


METHODS
A retrospective audit of OGTTs performed over an 18-month period in a teaching hospital in a major Australian city. Information gathered included co-morbidities; medications; risk factors for type 2 DM; indication for OGTT; results of OGTT and previous glucose 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 indication for OGTT was identified in 93%, including FPG 5.5-6.9 mmol/L (36%) and random plasma glucose (RPG) 5.5-11.0 mmol/L (19%). Other indications for OGTT identified included polycystic ovary syndrome or metabolic syndrome (8%), peripheral neuropathy (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 as stroke. Nineteen percent were taking medications known to affect plasma glucose (e.g. oral corticosteroids).


CONCLUSIONS
Only 55% of OGTTs had a previous FPG or RPG value warranting OGTT using current Australian DM guidelines. Other valid indications for OGTT were identified in the majority of the remainder. In addition, 41% were performed in the presence of confounding factors (such as acute illness or medications known to affect plasma glucose). Many of the OGTTs that are currently being performed are in the presence of confounding factors that could cause misleading results.
Ryan
Joshua
J
Pacific Laboratory Medicine Services (PaLMS), Royal North Shore Hospital, St Leonards, NSW 2065, Australia.
Siriwardhana
Deepani
D
Vasikaran
Samuel D
SD
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001315:Australia; D005260:Female; D005951:Glucose Tolerance Test / Q000592:standards*; D006784:Hospitals, Teaching; D006801:Humans; D008297:Male; D008875:Middle Aged; D055815:Young Adult