In 2019 the Endocrine Testing Area (ETA) at our tertiary hospital, had seen a significant increase in referrals for the Insulin Tolerance Test (ITT), to assess adult pituitary hormone reserve, for the application of growth hormone (GH). The ITT requires an intravenous dose of insulin to reduce the blood glucose level to below 2.5mmol/l, while observing hypoglycaemic symptoms. A room temperature fluoride glucose tube is recommended for collection. Accuracy of results was questioned, when examining the laboratory glucose results compared to the lack of symptoms observed by some patient’s. Senior scientists suggested a process known as glycolysis could result in a lower laboratory glucose level, and suggested an ice-water slurry or citrate tube to improve the accuracy as per the American Diabetes Association (ADA) guidelines.
The “Gold Standard” Yellow Springs Instrument Biochemical Analyser (YSI) was used to compare glucose results following the hospital and ADA guidelines for glucose tube handling and equipment:
Blood samples were collected at the same time point, from one syringe.
Due to significant patient insulin resistance, 16 time points were collected. Comparison of the YSI result, with the closest laboratory result, demonstrated the citrate tube, at room temperature was the most accurate at 76%, Fluoride tube on ice, 50% and fluoride tube at room temperature 0% with a difference of between 0.4-0.7mmol/l from the YSI value.
This small trial demonstrated the use of the fluoride tubes at room temperature as per the hospital guidelines provide the least accurate results. Larger studies need to be developed to assess the potential need for change in practice, handling and processing of glucose tubes to improve accuracy.