Uncontrolled Levothyroxine Replacement Therapy in Primary Care: Frequency and Associated Biochemical and Hematological Findings

Vollständiger Abstract

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Hypothyroidism is one of the most common endocrine disorders worldwide. Despite well-established levothyroxine (LT4) replacement therapy, achieving biochemical euthyroidism remains challenging. This study aimed to determine the frequency of uncontrolled LT4 replacement therapy and its associated biochemical and hematological findings in adults with primary hypothyroidism followed in primary care. This retrospective study included 157 adults with primary hypothyroidism receiving LT4 replacement therapy who attended Kamiloba Family Health Center, Istanbul, Türkiye, for routine follow-up. Patients were divided into overtreatment, euthyroid, and undertreatment groups based on serum TSH concentrations using reference values from the Istanbul Public Health Laboratory (0.27 < TSH < 4.80). Demographic, biochemical and hematological parameters were compared among the groups. Of the 157 patients, 137 (87.3%) were women (female to male ratio, 6.85:1), and the mean age was 60.9 ± 15.3 years. 9 patients (5.7%) were overtreated, 48 patients (30.6%) were undertreated, and 100 patients (63.7%) were euthyroid. The frequency of uncontrolled LT4 replacement therapy was determined 36.3%. Biochemical uncontrolled LT4 therapy was observed to be more frequent in women than in men (p = 0.007). HDL cholesterol levels were significantly lower in both the overtreatment (48.1 ± 11.8) and undertreatment (48.4 ± 11.8) groups than in the euthyroid group (53.7 ± 12.3) (p=0.021). Among hematological parameters platelet indices showed the strongest association with biochemical control status. Platelet count (PLT) was highest in the overtreatment group (321.2 ± 89.2) (p = 0.021). Platelet distribution width (PDW) was highest in the undertreatment group (16.2 ± 0.3) (p = 0.024). Plateletcrit (PCT) was highest in the overtreatment group (0.31 ± 0.07) and showed borderline significance (p = 0.069). Mean platelet volume (MPV) was highest in the undertreatment group (10.6 ± 1) ; however, the difference was not statistically significant (p = 0.166). In this primary care study, more than one-third of patients receiving LT4 replacement therapy had biochemical evidence of overtreatment or undertreatment. Uncontrolled LT4 replacement therapy was associated with lower HDL cholesterol levels and alterations in platelet indices, suggesting a potentially unfavorable cardiometabolic profile. These findings highlight the importance of regular biochemical follow up to optimize LT4 replacement therapy in primary care.