Up to 15 percent of all hypothyroid patients on levothyroxine only treatment have a reduced quality of life compared to healthy people. This applies to patients on levothyroxine even when their test results suggests that they are on a sufficient dosage. The reasons for this phenomenon, affecting about 0.5% of the population, are still uncertain.
Current research is helping to solve this problem. A new study has conducted detailed clinical investigations with added computer simulation, suggesting that today’s diagnostic practice may significantly contribute to poor quality of life in patients with hypothyroidism.
According to current guidelines, functional thyroid disorders are mainly assessed by means of the TSH test. Since TSH and the thyroid hormones triiodothyronine (T3) and thyroxine (T4) are closely interconnected, the supply of thyroid hormones may be better assessed by measuring all three levels. This also applies to assessing the dose for patients receiving levothyroxine. For cost efficiency it has repeatedly been suggested to measure TSH only. This practice may have severely adverse consequences for the achievement of health.
The study included more than 230 patients with different thyroid disorders and a similar sized group of thyroid-healthy people. In this collective group they repeatedly measured thyroid hormones and related the clinical findings with a mathematical approach. The results showed that the relationship between the hormones FT4 and TSH is more complicated than previously thought. Apart from the FT4 concentration, TSH levels also depend essentially on the set point of thyroid homeostasis (the point at which the various hormones act together for optimum patient outcome).
This observation was confirmed by computer simulation demonstrating that the set point can be modified by multiple variables. Based on these results the working group developed a theory of adaptive set points for a wide range of circumstances.
This study has profound implications for the future care of thyroid patients. It demonstrates that the TSH-only-centred approach commonly used in thyroid diagnostics may be ill-suited for a substantial portion of hypothyroid patients.
The current TSH-only paradigm has been adopted because of its perceived simplicity combined with the advantage of low diagnostic costs. However, the studies have shown that TSH concentrations do not accurately reflect the necessity of achieving adequate thyroid hormone levels for an acceptable quality of life. TSH measurement may be sufficient for screening of asymptomatic people but in patients who have hypothyroid or hyperthyroid symptoms, measurement of FT4 and FT3 appears to be better. This also applies to optimising therapy with levothyroxine.
Precise evaluation of thyroid function must address the complex interrelationships of the whole interactive system. Mathematical methods and computer simulations can aid in assessing the quality of laboratory methods and in increasing the discriminatory power of diagnostics.
Rudolf Hoermann, John E. M. Midgley, Rolf Larisch and Johannes W. Dietrich: Advances in Applied Homeostatic Modelling of the Relationship between Thyrotropin and Free Thyroxine.
You can access the paper here: journals.plos.org/plosone/a...