Interpreting TFT results

• Overt hypothyroidism (raised TSH and low FT4 - also seen in transient hypothyroid stage of subacute or postpartum thyroiditis)

• Subclinical hypothyroidism (TSH raised and FT4 normal)

• Secondary hypothyroidism - pituitary/hypothalamic disease (Low TSH and FT4)

• Poor adherence: taking excessive thyroxine prior to blood test (increased TSH and FT4)

• Other causes of abnormal TFTs: hospitalised people, amiodarone, lithium

Hypothyroidism

• Clinical consequence of deficient secretion by the thyroid gland. Common condition that often presents with non-specific symptoms. Levothyroxine (take before breakfast). Aged <50 (50-100mcg daily); aged >50 or cardiovascular disease (25mcg daily); adjust dose by 25-50mcg every 2-3 months. Target is TSH within reference range: typically 0.4-4.5 mU/L. Most people will become euthyroid with dose of 75-150mcg daily. Monitoring: not more frequently than every 2 months (TSH levels won't have stabilised). Once stabilised check annually. Hypothyroidism (CKS), Underactive thyroid - hypothyroidism (NHS Choices), ​British Thyroid Foundation​

Subclinical hypothyroidism (TSH < 10mU/L)

• Confirm by repeating TSH, T4, and thyroid peroxidase antibodies (TPO-Ab) in 3-6 months. Thyroxine not routinely indicated, but consider if patient has goitre, TSH is rising, pregnant (current or planning), patient has symptoms of hypothyroidism. If treatment started, aim to maintain TSH in reference range, check TSH annually once stable. If treatment not started, monitor TSH annually (if TPO-Ab present), every 3-years (if no TPO-Ab). Subclinical hypothyroidism (Patient.info)

Hypothyroidism in pregnancy

• Pre-conception: check TSH and free T4 to check adequacy of treatment. Refer if the woman has a history of Graves' disease. Advise the woman to consult her GP as soon as she thinks she may be pregnant

• If pregnant: Refer. At diagnosis of pregnancy, immediately increase the levothyroxine dose and check TSH and FT4 levels while waiting for referral to a specialist. Dose should be increased usually by adding at least 25–50 mcg levothyroxine; the size of the initial increase in dose will depend on the dose the woman is already taking and the TSH and FT4. A 30–50% increase in dosage may be required. Check TSH and FT4 levels every 4 weeks until stabilized, aiming for a TSH concentration in the low-normal range (0.4–2.0 mU/L) and an FT4 concentration in the upper reference range. Monitor TSH and FT4 levels every 4 weeks during titration of levothyroxine, every 4 weeks during the first trimester, and again at 16/40 and at 28/40, in a woman who is on a stable dose of levothyroxine. More frequent tests may be appropriate on specialist advice.​

Hyperthyroidism

• Hyperthyroidism (CKS), Overactive thyroid (NHS Choices)

Thyroiditis

• Thyroiditis (NHS Choices)

RCGP, July 2024:

• A 30-year-old woman has developed a small goitre and palpitations four months after the birth of her first child.  She is breast feeding. On examination she has a sinus tachycardia of 100 beats/minute. Her thyroid function shows: Thyroid stimulating hormone (TSH) < 0.1 mU/l (reference range 0.4–4 mU/l); free T4 30 pmol/l (reference range 9.0–20 pmol/l).

• Post-partum thyroiditis occurs in 10% of all pregnancies. There are two forms: 1) Destructive – remits spontaneously and has a low uptake of radio-iodine; and 2) Post-partum exacerbation of autoimmune Graves' disease – positive thyroid stimulating immunoglobulin (TSI) and high radioiodine uptake. A quarter of patients with post-partum thyroiditis progress to hypothyroidism in five years.

​Thyroid cancer

• Cancer of the thyroid (NHS Choices)