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| First author, year (ref.) | Fade, 1991 [13] | Somwaru, 2012 [16] | Rosário, 2016 [15] | Li, 2017 [14] |
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| No. of patients; gender; and country | 1193 over 60 yrs old; women (n = 700) and men (n = 510); and Birmingham, United Kingdom | 459, at least 65 yrs old; women (n = 282) and men (n = 177); and USA communities | 241 individuals of 20–71 yrs; women (n = 241); and Minas Gerais, Brazil | 505 patients of 40 yrs or older; women (n = 168) and men (n = 138); and Shandong Province, China |
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| Definition | Without being explicit, they define Shypo as abnormal TSH results, but normal free thyroid hormone (FT4)-TSH shows a positively skewed distribution with a reference limit of 0.5 to 5 mIU/L | Shypo was defined as having TSH of 4.5–19.9 mIU/L with a normal FT4 | Shypo was defined as TSH being persistently >10 mIU/L, confirmed at an interval of 12 weeks | Shypo was defined by elevated TSH (mild TSH ≤10 mIU/L or severe TSH >10 mIU/L), with normal free thyroxine (FT4) |
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| Limit of detection (LoD); TSH assay and method | 0.1 mIU/L; MAIA-clone method (Serono Diagnostics) | 0.005 mIU/L; Elecsys 2010 analyzer (Roche Diagnostics, Indianapolis, IN) | Assay range is 0.004–75 mIU/L; Immulite 2000 (Diagnostic Products Corporation) | Measuring range 0.005–100 mIU/L; Cobas E601 (Roche, Basel, Switzerland) |
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| Follow-up of patients (years) | 1 | 4 | 5 | 3 |
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| TSH (mIU/L) associated with an increased probability of overt hypothyroidism | 10 | 10 | 8 | 7 |
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| Antithyroid antibodies and other factors related to progression to overt hypothyroidism | Progression to overt hypothyroidism was common in patients with antithyroid antibodies. 46% of patients with over 5 mIU/L TSH had antithyroid antibodies. 81% of patients with over 10 mIU/L TSH had antithyroid antibodies | Antithyroid peroxidase (anti-TPO) status. 35% of Shypo patients were TPOAb positive | | Patients with total cholesterol >240.0 mg/dL had a greater risk of developing Shypo. TPOAb >34 IU/mL at higher risk of developing Shypo |
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| Frequency of clinical and laboratory changes | The prevalence of abnormal TSH in patients was 13.8%. An inverse correlation was seen between TSH and FT4 in patients with TSH >5 mIU/L. High TSH values continued in 76.7% of patients for 12 months | 69% with Shypo had TSH between 4.5 and 6.9 mIU/L. 56% of patients had persistent Shypo. 2%, at yr 2, developing overtly hypothyroid. 32%, at yr 4, were again Shypo | 58.1% of patients had persistent Shypo. 19% of patients developed overt hypothyroidism | 43.8% of patients had persistent Shypo. 3.4% of patients developed overt hypothyroidism |
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| Frequency of TSH normalization | 5% of patients had normalized TSH in 12 months | 35% of patients had normalization of serum TSH at yr 2. 48% of patients who had reverted TSH remained euthyroid at yr 4. 45% of patients who had not reverted TSH had TPOAb at yr 4; 8% of patients had normalization in all samples at yrs 2 and 4 | 22.8% of patients had normalization of serum TSH at yr 5; and 51.5% of these were anti-TPO-negative patients | 49.7% of patients had normalization of TSH serum |
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