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Abnormalities of serum thyrotropin concentrations are often transient
The background of the study. Subclinical thyroid disease, as defined by high or low serum thyrotropin (TSH) concentrations but normal serum free thyroxine (T4) concentrations, is common. This study was done to determine the frequency with which physicians ordered measurements of serum TSH and the course of patients with subclinical thyroid disease if left untreated.
How the study was done. The study group consisted of all patients enrolled in a health plan in Israel in whom serum TSH was measured (normal range, 0.35 to 5.5 mU/L) during 2002 and who were followed through 2006.
The results of the study. Serum TSH was measured at least once in 422,242 patients, 18 percent of those enrolled in the plan. The values were abnormal in 21,003 patients (5.0 percent) (Table 1).
| Table 1. Initial Serum TSH Concentrations in 422,242 Outpatients. | |||
| Serum TSH (mU/L) | Women | Men | Total |
| Normal | 262,071 (62%) | 139,168 (33%) | 401,239 (95%) |
| >10 | 2,348 (0.5%) | 715 (0.2%) | 3,063 (0.7%) |
| >5.5 to <10 | 9,991 (2.4%) | 2,824 (0.7%) | 12,815 (3.0%) |
| <0.35 | 3,745 (0.9%) | 1,380 (0.3%) | 5,125 (1.2%) |
Serum free thyroxine (T4) was measured in 89 percent of the patients who had abnormal serum TSH values. The values were normal in 70 percent of those with serum TSH values >10 mU/L and 93 percent of those with values >5.5 to 10 mU/L, indicative of subclinical hypothyroidism, and in 91 percent of those with serum TSH values <0.35 mU/L, indicative of subclinical hyperthyroidism.
Serum TSH was measured two or more times in 346,549 patients (85 percent), on average 19 months later. Nearly all patients with normal values when first tested had normal second values (Table 2), as did many of those whose first value was abnormal. Among the patients whose first serum TSH value was slightly high (>5.5 to 
10 mU/L), only 2.9 percent had higher second values (>10 mU/L).
| Table 2. Results of Second Serum TSH Measurements in 346,549 Outpatients. | ||||
| Second Serum TSH (mU/L) | First Serum TSH (mU/L) | |||
| Normal | >10 | >5.5 to <10 | <0.35 | |
| (n = 334,572) | (n = 669) | (n = 7533) | (n = 3775) | |
| Normal | 98% | 28% | 62% | 52% |
| >10 mU/L | 0.1% | 35% | 2.9% | 0.6% |
| >5.5 to 10 mU/L | 1.4% | 36% | 35% | 1.2% |
| <0.35 mU/L | 0.6% | 0.4% | 0.3% | 47% |
| Percentages do not add to 100 because of rounding. | ||||
The conclusions of the study. The frequency of abnormal serum TSH concentrations is low in outpatients. When tested again, the second value is normal in nearly all patients whose first value was normal and in most patients whose first value was abnormal. Any abnormality in serum TSH should be confirmed before therapy is started.
The original article. Meyerovitch J, Rotman-Pikielny P, Sherf M, Battat E, Surks MI. Serum thyrotropin measurements in the community: five-year follow-up in a large network of primary care physicians. Arch Intern Med 2007;167:1533-8.
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| Thyroid Digest Index | | | November 2007 Thyroid Digest |
