TSH Normal Range by Age

Lab Tests Online UK notes, for blood tests generally, that your report will include the reference ranges used by your laboratory, and TSH is no exception: the range that applies to you is the one printed on your own report. Lab Tests Online UK describes TSH as a test whose result is usually followed by free T4 and sometimes free T3 if it is abnormal, and notes that neither a high nor a low TSH tells you the reason by itself.

The sources read here express TSH as mIU/L or mU/L, and when you look up a number online it is worth comparing it with the range printed on your own report rather than assuming it matches.

To show how bands change across life, here are the age-related ranges published by Exeter Clinical Laboratory International, a UK laboratory, in a procedure revised in February 2024. They are one laboratory's figures, not a national standard, and other laboratories use different values.

In most adults one band is applied across the whole adult age span, but there is a debate about whether this is right for older people. A cross-sectional study of 2,460 people aged 65 and over in China, published in Scientific Reports in 2022, proposed age-specific reference ranges of 0.65 to 5.51 mIU/L for ages 65 to 70, 0.85 to 5.89 for 71 to 80, and 0.78 to 6.70 for those over 80.

Using those age-specific ranges, the study found the prevalence of subclinical hypothyroidism was 3.74 percent, compared with 10.28 percent using the laboratory reference range, and the authors concluded that an age-specific range can help prevent overdiagnosis in the elderly. This is one study in one population, and it is not UK guidance, so it should be read as a reason why a slightly raised TSH in an older adult is interpreted with care rather than a new standard.

NICE Clinical Knowledge Summaries notes that symptoms of hypothyroidism may be mild and non-specific, especially in the elderly, such as fatigue, cold intolerance, weight gain, constipation and depression, which is another reason a borderline number is not read in isolation.

Age is only one factor. Lab Tests Online UK says thyroid hormone replacement and some drugs, for example lithium and amiodarone, may interfere with results, that extreme stress and acute illness can affect TSH, which is known as non-thyroidal illness, and that TSH may be low during the first trimester of pregnancy.

The same source says that when a thyroid hormone dose is adjusted you should wait at least 6 weeks before checking TSH again, so the new dose has had its full effect, and that TSH should not routinely be measured more often than every 6 weeks.

A TSH just outside the range, with a normal free T4, is the situation described as subclinical thyroid disease. NICE CKS defines subclinical hypothyroidism as TSH above the reference range with T3 and T4 within the range, and subclinical hyperthyroidism as TSH below it with FT4 and FT3 within range, and in both cases repeat testing is part of the approach.

The NHS notes that the symptoms of an underactive thyroid may be mild and not easy to notice, and that a GP may arrange TSH and thyroxine blood tests. What matters is the pattern: the TSH, the free T4, how you feel, your age, pregnancy status and medicines, and how the numbers have behaved on repeat testing.

• Compare your TSH with the range printed on your own report, not a table from another source.

• Ask whether free T4 was measured alongside it.

• Note recent illness, pregnancy, biotin supplements and medicines such as lithium and amiodarone.

• Expect a repeat test, usually after several weeks, before a decision is made about a borderline result.