Thyroid compounds are a group of hormones responsible for the regulation of a variety of biological functions, including basal metabolic rate, lipid, glucose and carbohydrate metabolism. This group of compounds contains tyrosine base compounds including the physiologically active form triiodothyronine (T3).
The majority of triiodothyronine is form enzymatically by the deiodination of thyroxine (T4). T4 can also be deiodinated to form an inactive form of T3 called reverse-triiodothyronine (rT3). Normal thyroid hormone reference intervals have a large degree of variability base on a number of factors including age, sex and ethnic origin of the population; the range is calculate base on a 2.5th to 97.5th percentile of a normal population with a seemingly healthy thyroid function.
The main medical conditions
There are two main medical conditions associate with thyroid hormone levels: hyperthyroidism and hypothyroidism. Hyperthyroidism is cause by elevate level of triiodothyronine and is clinically indicate by a low thyroid-stimulating hormone level and an elevate T4 and/or T3 concentration.
Symptoms of which includes excessive weight loss, heat intolerance, tremor; so rapid heart rate and palpitations and if left untreate; so can cause heart failure, osteoporosis, eye problems and miscarriage. This paper investigates the simultaneous analysis of “free” thyroid hormones using LC-MS in blood serum; “free” thyroid hormones are define as those that are not protein-bound in the blood.
Our analytical capabilities allow analysis of “free” thyroid hormones by low resolution; hence using an ion trap mass spectrometer, and high resolution using an orbitrap mass spectrometer. The results are compare, in a blind study; so with samples run using clinical routine testing methods base on immunoassay (ECLIA and ELISA). The benefits of the LC-MS approaches are compare.
Sample extraction recoveries
LC-MS methods for the analysis of “free” thyroid hormones have previously publish; however, these have show a large variation in sample extraction recoveries and precision data. Therefore, offering limit improvements on the currently use ECLIA method. These papers also have limit comparison of new with existing establish methodologies; also those which have included comparison show limit correlation between the methods.
Although not test as part of this study, automation could also be use by utilising autosampler programing to perform sample dilution on the high-resolution LC-MS method and the possibility of in line SPE for the low-resolution LC-MS method. The high-resolution LC-MS method shows the greatest improvement in terms of sensitivity and analysis time; however, due to the increase in capital cost, this may be less favourable in certain laboratories.
Therefore the low resolution LC-MS method would be a useful compromise as the increase in sensitivity and reduction in analysis time would still be achievable; but with a reduce capital expenditure. With both LC-MS methods, there would be a requirement for staff training in the form of software training and/or SPE training; which would need to be factor into expenditure costs.