Pulmonary consequences of hypothyroidism.

Sir,

I have read with interest the case–control study by Sadek et al. on the pulmonary consequences of hypothyroidism in a cohort of Egyptian patients.[1] In the methodology, the authors employed spirometry to measure various components of pulmonary function tests (PFTs), namely, forced vital capacity (FVC), FVC%, forced expiratory volume in 1 s (FEV1s), FEV1s%, FEV1s/FVC, and forced expiratory flow (FEF25–75)%.[1] The authors found that FVC% and FEF25–75% were significantly reduced in the hypothyroid group (P = 0.014, P = 0.000, respectively)compared to the control group.[1] I presume that these findings ought to be cautiously interpreted. My presumption is based on the presence of the following methodological limitation. It is obvious that the evaluation of PFTs is usually done by examining the absolute values of various PFTs components, comparing them with predicted values, and examining the shape of the curves. Precise interpretation of PFTs in particular patients compared to the matched controls requires population-specific reference values (RVs). There are many population-specific RVs of PFTs.[23] The authors did not state which RVs were employed in their study. To my knowledge, the only available Egyptian RVs based on age and height were constructed more than two decades ago for healthy nonsmokers female industrial workers,[4] and they are no more useful in the clinical field and researches. Since normal pulmonary function tends to be genetically, nutritionally, physiologically, environmentally, socioeconomically, and ethnically determined,[5] it is pivotal to construct new Egyptian population-specific prediction equations to establish RVs of PFTs. I presume that the employment of national RVs might change the Sadek et al's study results.

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