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. Aim: To evaluate indications, outcomes and confounding factors of OGTTs performed at a large teaching hospital and to compare them with Australian DM guidelines. Method: 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). Conclusion: 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.
Thyroid stimulating hormone (TSH) secretion shows a circadian rhythm, affecting free thyroxine (fT4) secretion in the same manner. Samples are collected randomly throughout the day for serum TSH & fT4 measurement in current practice. This may affect interpretation of results if the follow up samples are collected at different times of the day from the same individual. We aimed to assess the diurnal variation in serum TSH and fT4 levels in healthy adults. Healthy adult volunteers with Sinhalese ethnicity aged 21 -50 years were selected for the study. Subjects with thyroid or any other disease, on medications including oral contraceptives and postmenopausal women were excluded. Two blood samples were drawn from each subject at 8-9 am and 3-4 pm on the same day. TSH and fT4 were measured using VITROS ECi Immunodiagnostic system. Paired T test was used to assess whether there was a statistically significant diurnal variation in hormone values. Data were analyzed using IBM SPSS Statistics Version 20 and Microsoft Excel 2013. A total number of 36 subjects with an equal number of males & females participated in the study. There was no variation in hormone levels due to age or gender. Log transformed TSH and fT4, showed a statistically significant difference for both TSH (p=0.013) and freeT4 (p<0.001) values in the morning and afternoon. Standardization of sample collection time may be important for TSH and fT4 hormone assays as this study revealed a statistically significant diurnal variation for both hormones. However further studies are needed in patients with thyroid diseases and individuals of other age groups as well to ascertain the clinical significance.
The correct volume of sample and time of storing prior to the analysis are important considerations in the estimation of plasma glucose concentration of patients. The present study was to determine the effect of sample volume variation and time delay in the analysis of plasma glucose results in healthy adults. A total of 30 individuals aged between 20 and 30 years were selected for the study. Blood samples were collected into three fluoride-oxalate collection tubes separately. The results revealed that the sample volume variation from 2.0 mL fluoride-oxalate tube to 1.0 mL and 3.0 mL did not significantly affect the plasma glucose concentration ( p > 0.05). However, the plasma glucose concentration in the sample significantly decreased upon delaying the analysis. The mean fasting plasma glucose concentration of analysis after one hour of collection and analysis after three hours of collection was not significantly different ( p > 0.05). The mean fasting plasma glucose concentrations between one hour and five hours timepoints after collection ( p < 0.001) and between three hours and five hours after collection ( p = 0.014) were significantly different. In conclusion, overfilling and underfilling (2.0 ± 1.0 mL) of fluoride-oxalate tubes did not affect the plasma glucose results significantly. If the samples are analyzed within three hours of collection, the time dependent change too is not statistically significant.
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