Effect of Sample Volume Variation and Delay in Analysis on Plasma Glucose Concentration in Sri Lankan Healthy Adults.

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.

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. 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.

Thyroxine autoantibody interference is an uncommon cause of inappropriate TSH secretion using the Immulite 2000 assay.

BACKGROUND: Inappropriate TSH secretion, as defined by an elevated free thyroxine (fT4) and non-suppressed thyrotropin (TSH) result, can be caused by acute illness, medications, TSH secreting tumours, thyroid hormone resistance or immunoassay interference including thyroid hormone autoantibody interference. T4 autoantibody (T4AAb) prevalence has not been determined. We determined the prevalence of inappropriate TSH secretion using the Immulite 2000 assay and the prevalence of T4AAb within this subgroup. METHODS: Samples were stored over 13 months and thawed once for batch analysis. T4AAb was detected using radioimmunoprecipitation with >5% of the radiolabel within the immunoprecipitate indicating true positivity. All case notes and medication charts were reviewed. RESULTS: Of 13,286 thyroid profiles reviewed, 85 (0.64%) samples demonstrated inappropriate TSH secretion. One of these 85 samples (1.2%) was positive for T4AAb with a radioimmunoprecipitate of 21%. 46/85 (54%) samples were collected on hospitalised patients, 7 patients were prescribed amiodarone, 12 patients were taking beta blockers, 30 patients were on thyroxine replacement and 7/85 (8%) were collected on outpatients not taking medication known to affect thyroid function. CONCLUSION: T4AAb interference is an extremely rare explanation for inappropriate TSH secretion with the Immulite 2000 assay but should be excluded before investigating for rarer causes of this biochemical picture.