Harmonisation and standardisation of thyroid function tests is the need of the hour

On World Thyroid Day, Dr Barnali Das, consultant, biochemistry & immunology, Kokilaben Dhirubhai Ambani Hospital & Medical Research Institute, Mumbai, India explains the importance of ethnicity-specific cut offs for Thyroid Function Tests

25 May is World Thyroid Day. Thyroid is a small gland in our body, which together with pituitary gland and hypothalamus, work as a well-orchestrated triad, controlling the level of thyroid function tests in our blood. They act like a mini-orchestra, creating and maintaining the hormonal and biochemical symphony in our body. However, in spite of a large body of knowledge in the medical fraternity, the functioning of this very important gland has thrown up new mysteries.

This is because of findings in recent years, which have highlighted overt simplification in our prevalent understanding of the way the triad of organs produce and release thyroid hormones in our blood.

Thyroid Function Tests (TFTs) form a very important set of tests in a laboratory; a tool that clinicians and patients alike depend on, to pin down the symptoms for treatment and relief.

However, it is this very set of tests that have come in question. First, what is the normal and acceptable range (upper and lower limits) of TFTs in a particular population, has been debated in different scientific fora. This is because, the level of markers can change in relation to other biochemicals, biomolecules and hormones, which themselves vary considerably with race, gender, age, different physiological conditions (like pregnancy, new-born) and other illnesses and interfering substances. This variation can be to such an extent that, each individual may seem to have their own set-point of these hormones, as an example, for that of thyroid stimulating hormone (TSH).

Therefore, harmonisation of procedures is the need of the hour, since a major problem clinicians and diagnosticians have to grapple with is the variability of test-results; even a broadly similar set of instruments and methods can provide different results, even as much as 10-40 per cent more or less, for example, in case of TSH values. It is then a real challenge to the physician to decide whether the patient is suffering from a disease or is it something else, since other factors can also cause changes in test levels.

Due to the lack of proper reference intervals and sometimes due to standardised measurement procedures, standardisation and harmonisation of TFT still remains a formidable challenge

Ethnicity-specific cut off of TFTs is important for accurate test reports. I was associated with IFCC Committee on Standardisation of Thyroid Functions Tests (C-STFT) and am currently corresponding with C-STFT from IFCC Scientific Division. In India, we organised free thyroid camps for few years and every year around 1000 TSH screenings were done during World Thyroid Day.

Based on the population demographic variations, we have established reference interval for TSH and FT4 in Indian population. This study was conducted in Kokilaben Dhirubhai Ambani Hospital & Medical Research Institute. We have screened 800 subjects. 629 healthy subjects were chosen in the study group for reference interval verification.

The reference interval IU/ml (90 per cent confidence interval) for TSH by non-parametric procedure (bootstrap) is 0.48-4.52, and by parametric one (after transformation of the data), it is 0.45-4.27 IU/ml for the adult population, which is little different from the manufacturer’s claim.

We have also verified accuracy and precision, analytical measurement range (AMR) and extended measuring interval (EMI) of TFTs.

The globalisation places a responsibility on us to reduce the current variability in patient results for Thyroid Function Tests, which arises from differences between methods, and laboratory practices. The roadmap for laboratory medicine, therefore, will involve strategies for harmonising, communicating, and integrating with all stakeholders, such as clinicians, diagnosticians, and IVD industry, in order to formulate guidelines for assisting in correct measurement, diagnosis, and management of diseases.