📚 Module Overview
Hypothyroidism, or an underactive thyroid, is a common endocrine disorder where the thyroid gland does not produce enough thyroid hormones. These hormones regulate the body's metabolism, and their deficiency leads to a general slowing down of bodily functions. The most common cause in the UK is autoimmune thyroiditis (Hashimoto's disease). While symptoms can be vague, diagnosis is straightforward with blood tests, and treatment with levothyroxine is simple, safe, and effective.
On completion of this module, you will be able to:
- Identify the common causes and symptoms of hypothyroidism.
- Describe the diagnostic pathway based on TSH and T4 levels, according to NICE guidelines.
- Differentiate between overt and subclinical hypothyroidism.
- Outline the principles of initiating and monitoring levothyroxine treatment.
- Counsel patients on how to take levothyroxine correctly and manage common issues.
- Recognise situations that require troubleshooting, such as persistent symptoms despite treatment.
🔬 Diagnosis in Primary CareNICE NG145
Diagnosis should not be based on symptoms alone. The NICE guideline (NG145) provides a clear pathway for investigation.
Who to Test?
Consider testing for hypothyroidism in patients with:
- Symptoms such as fatigue, weight gain, constipation, dry skin, and low mood.
- Type 1 diabetes or other autoimmune diseases (e.g., coeliac disease).
- New-onset atrial fibrillation.
- A history of neck radiotherapy or thyroid surgery.
- A history of taking drugs known to affect thyroid function, such as lithium and amiodarone.
Interpreting Blood Results
The initial test is for Thyroid-Stimulating Hormone (TSH). If the TSH is abnormal, the lab will automatically add a test for free thyroxine (T4).
| TSH Level | Free T4 Level | Interpretation | Action |
|---|---|---|---|
| High (>4.2 mU/L) | Low (<9.1 pmol/L) | Overt Hypothyroidism | Offer treatment with levothyroxine. |
| High (>4.2 mU/L) | Normal | Subclinical Hypothyroidism | Consider a trial of treatment if TSH >10 or if symptomatic with TSH between 4.2-10. |
| Normal | Normal | Euthyroid (Normal function) | Hypothyroidism unlikely. Consider other causes for symptoms. |
| Low | Low or Normal | Secondary Hypothyroidism | Rare. Suggests a pituitary problem. Requires urgent endocrinology referral. |
Consider checking TPO antibodies in adults with a raised TSH. High levels confirm an underlying autoimmune cause (Hashimoto's thyroiditis), which helps predict progression from subclinical to overt hypothyroidism.
🧭 Management Principles
The goal of treatment is to restore the patient to a euthyroid state, resolving symptoms and normalising the TSH level. The sole treatment for primary hypothyroidism is hormone replacement with levothyroxine (synthetic T4).
Initiating Levothyroxine
- For most adults under 65 with no history of cardiovascular disease: Start with a full replacement dose based on weight: 1.6 mcg/kg/day (rounded to the nearest 25 mcg).
- e.g., a 70kg person would start on ~112mcg, so a practical starting dose would be 100mcg or 125mcg.
- For adults aged 65+ or with a history of cardiovascular disease: Start with a lower dose of 25-50 mcg daily and titrate upwards slowly every 3-4 weeks to avoid provoking cardiac symptoms like angina or arrhythmias.
Monitoring
- After starting or changing a dose, re-check TSH and T4 levels after 8-12 weeks.
- Once the TSH is stable within the reference range, monitoring can be reduced to annually.
- The aim is to maintain the TSH within the normal reference range (typically 0.4-4.2 mU/L). There is no evidence of benefit from aiming for the lower end of the normal range.
💊 Pharmacology Focus: LevothyroxineBNF
Levothyroxine is a simple and effective medication, but correct administration and awareness of interactions are crucial for optimal effect.
Levothyroxine has poor and variable absorption. To ensure consistency, it should be taken:
- Preferably 30-60 minutes before breakfast or other medications.
- On an empty stomach, with a glass of water.
- Consistently at the same time each day.
Common Interactions Affecting Absorption
Many common substances can bind to levothyroxine in the gut and prevent its absorption. Patients should be advised to leave a gap of at least 4 hours between their levothyroxine and:
| Substance | Examples |
|---|---|
| Minerals & Antacids | Calcium supplements, Iron supplements (e.g., ferrous sulfate), Indigestion remedies (e.g., Gaviscon), some multivitamins. |
| Foods | Soya, coffee, high-fibre foods (e.g., bran). |
| Other Medications | Proton Pump Inhibitors (PPIs) like omeprazole, cholestyramine. |
🔧 Troubleshooting & Special Scenarios
Sometimes, patients remain symptomatic despite having a "normal" TSH on their blood test. This requires a systematic approach.
Persistent Symptoms with Normal TSH
- Check Adherence: Is the patient taking their medication correctly and consistently?
- Review for Absorption Issues: Are they taking it with food, coffee, or interacting medicines? Do they have an undiagnosed condition affecting absorption, like coeliac disease?
- Consider Brand Consistency: A small number of patients report symptoms when their brand of levothyroxine is changed. The MHRA advises that if a patient feels well on a specific brand, consistent prescribing of that brand should be considered.
- Look for Other Causes: Hypothyroid-like symptoms (fatigue, weight gain) are very non-specific. Consider other diagnoses like depression, menopause, anaemia, or simply lifestyle factors.
Some patients feel that adding T3 (liothyronine) to T4 (levothyroxine) improves their symptoms. However, NICE and the British Thyroid Association do not recommend this for routine use due to a lack of evidence for benefit and potential long-term safety concerns (e.g., arrhythmias, osteoporosis).
Initiation of T3 is a specialist-only decision for a small subset of patients who remain symptomatic despite optimal levothyroxine therapy, and should not be started in primary care.
🎯 OSCE Preparation
Counselling a Newly Diagnosed Patient on Levothyroxine
Scenario: A 45-year-old woman is collecting her first prescription for Levothyroxine 100mcg daily after being diagnosed with hypothyroidism.
Key Communication & Counselling Steps:- Explain the Condition & Medicine: "Your blood tests show your thyroid gland is a bit underactive. This tablet, levothyroxine, is simply a replacement for the hormone your thyroid isn't making enough of. It should help with symptoms like tiredness and weight gain."
- Give Clear Administration Instructions: "This is the most important part for making sure the medicine works properly. You need to take one tablet, first thing in the morning, on an empty stomach with a glass of water. Then wait at least 30 to 60 minutes before you have your breakfast, your first cup of tea or coffee, or any other medicines."
- Explain the Monitoring Plan: "It will take a while for the hormone levels to settle. The doctor will do a blood test in about 2-3 months to check the dose is right for you. Once we find the right dose, you'll just need a blood test once a year."
- Manage Expectations: "It's not an instant fix; it can take a few weeks or even a couple of months to feel the full benefit, so please be patient with it. It's really important you take it every day."
- Check for Interactions: "Do you take any other regular medicines, or any supplements like iron or calcium tablets? It's important to leave a 4-hour gap between your levothyroxine and those."
- Safety Netting & Teach-Back: "This is a lifelong treatment, so it's important to get into a good routine. To make sure I've explained that clearly, can you tell me the best way to take your tablet each morning?"
⭐ Bonus: Clinical Pharmacist Case Study
The Patient: Poorly Controlled TSH
Patient Profile: Mr. Davies, a 68-year-old man, has been on Levothyroxine 125mcg for several years. His annual blood test shows his TSH has risen to 15.2 mU/L (up from 3.5 last year). He says he feels "more tired than usual".
The Challenge: The GP is about to increase his dose, but asks for your input first.
Pharmacist's Thought Process & Plan
- Subjective: Reports increased fatigue.
- Objective: TSH is high, indicating under-replacement.
- Assessment:
- The TSH is high, so the dose is currently insufficient. The immediate thought is to increase the dose, but first, we must investigate *why* it's insufficient.
- Differential Diagnosis for high TSH on treatment:
- Non-adherence: Is he taking it every day?
- Malabsorption: Has his routine changed? Is he now taking it with breakfast or coffee? Has he recently started a new interacting medicine (e.g., a calcium supplement for osteoporosis, or omeprazole for indigestion)?
- Increased demand: Has he gained a significant amount of weight?
- Plan:
- Action: Speak to the patient before the GP increases the dose.
- Patient Interview: "Mr. Davies, I can see your thyroid level is a bit high. Can you talk me through exactly how you take your levothyroxine tablet each day? What time do you take it? What do you have with it? Do you have breakfast straight away? Have you started any new tablets recently, even over-the-counter ones for indigestion or vitamins?"
- Discovery: The patient reveals he was recently prescribed omeprazole for reflux and has been taking it at the same time as his levothyroxine in the morning.
- Intervention & Recommendation to GP: "The likely cause of Mr. Davies' high TSH is a drug interaction with his new omeprazole, which is reducing the absorption of his levothyroxine. Before increasing the dose, I recommend we first manage the interaction. I have advised him to continue taking his levothyroxine first thing, but to wait until bedtime to take his omeprazole. We should re-check his TSH in 8-12 weeks. An unnecessary dose increase can be avoided."