top of page
Search

TFTs: Subclinical and Overt Disease — MRCP Part 1

TL;DR:

Subclinical and overt thyroid disease are distinguished by biochemistry, not symptoms. For MRCP Part 1, most questions test pattern recognition on TFTs, common causes, and when not to treat. This article provides a high-yield framework, exam traps, and a short MCQ to secure easy marks.


Why this topic matters for MRCP Part 1

Thyroid function tests (TFTs) are among the most frequently examined investigations in MRCP Part 1. Candidates commonly lose marks by:

  • confusing subclinical with overt disease,

  • treating biochemical abnormalities prematurely, or

  • misinterpreting TFTs during acute illness.

Examiners favour clear definitions, common causes, and management thresholds rather than nuanced endocrinology. Mastery here is efficient score-gain.

For syllabus context, see the official MRCP Part 1 overview:https://www.mrcpuk.org/mrcpuk-examinations/part-1


Core definitions (must-know)

Thyroid status is defined using TSH and free thyroid hormones (FT4 ± FT3).

TSH

Free T4

Diagnosis

↑

Normal

Subclinical hypothyroidism

↑

↓

Overt hypothyroidism

↓

Normal

Subclinical hyperthyroidism

↓

↑ (± FT3)

Overt hyperthyroidism

Normal / ↓

↓ FT3

Non-thyroidal illness

Exam rule: Symptoms do not define subclinical disease — biochemistry does.

The 5 most tested subtopics

1. Subclinical hypothyroidism

  • Raised TSH with normal FT4

  • Most commonly autoimmune (Hashimoto’s thyroiditis)

  • Often asymptomatic

  • Risk of progression increases with:

    • TSH >10 mIU/L

    • positive thyroid peroxidase (TPO) antibodies

Treatment in exams: Usually observe. Consider levothyroxine if TSH >10, pregnancy, or significant symptoms.

2. Overt hypothyroidism

  • Raised TSH, low FT4

  • Causes: autoimmune disease, iodine deficiency, post-radioiodine, drugs

  • Associated findings:

    • hypercholesterolaemia

    • hyponatraemia

    • macrocytosis

Exam rule: Overt hypothyroidism is treated unless transient or drug-related.

3. Subclinical hyperthyroidism

  • Suppressed TSH with normal FT4/FT3

  • Causes:

    • early Graves’ disease

    • toxic multinodular goitre

    • excess thyroxine

Why it matters:

  • Increased risk of atrial fibrillation

  • Increased bone loss in older adults

Exam rule: Do not treat immediately unless high-risk or persistent.

4. Overt hyperthyroidism

  • Suppressed TSH with raised FT4 and/or FT3

  • Graves’ disease most common cause

  • Complications:

    • atrial fibrillation

    • weight loss

    • osteoporosis

Exam trap: A low TSH alone is not enough — hormones must be elevated.

5. Non-thyroidal illness (euthyroid sick syndrome)

  • Low FT3 ± low FT4

  • TSH low, normal, or slightly raised

  • Occurs in acute illness, surgery, sepsis

Critical exam point:✔ No thyroid treatment✔ Repeat TFTs after recovery


MRCP Part 1 study setup with endocrinology notes and thyroid function test revision material

10 high-yield exam facts (numbered)

  1. TSH is the most sensitive screening test.

  2. Subclinical disease is biochemical, not clinical.

  3. Treat subclinical hypothyroidism only if clear indications exist.

  4. Elderly patients are harmed more by overtreatment than mild hypothyroidism.

  5. Subclinical hyperthyroidism increases AF risk in patients >65 years.

  6. Acute illness commonly distorts TFTs.

  7. Amiodarone can cause both hypo- and hyperthyroidism.

  8. Always check medications before diagnosing thyroid disease.

  9. Repeat TFTs before committing to treatment.

  10. Most MRCP questions are pattern-recognition based.


Mini-MCQ (MRCP style)

Question A 72-year-old man is incidentally found to have TSH 0.09 mIU/L (0.4–4.5) with normal FT4 and FT3. He is asymptomatic and clinically euthyroid. What is the most appropriate management?

A. CarbimazoleB. PropranololC. Observe and repeat TFTsD. RadioiodineE. Start levothyroxine

Correct answer: C

Explanation: This is subclinical hyperthyroidism. In an asymptomatic patient, initial management is observation with repeat TFTs. Treatment is reserved for persistent disease or high-risk patients (e.g. atrial fibrillation).

Practise similar questions in the Crack Medicine Qbank:https://crackmedicine.com/qbank/


Common pitfalls (5 examiner favourites)

  • Treating subclinical disease without indications

  • Diagnosing hypothyroidism during acute illness

  • Ignoring drug effects (amiodarone, steroids)

  • Over-relying on symptoms instead of TFTs

  • Forgetting age-related risks in subclinical hyperthyroidism


Practical study checklist

  • Memorise TFT patterns as a table

  • Practise endocrine MCQs weekly

  • Flag questions involving acute illness

  • Always check TSH and FT4 together

  • Revise alongside structured teaching

Recommended companion resources:


FAQs

What defines subclinical hypothyroidism?

Raised TSH with normal free T4. Symptoms are not required for diagnosis.

When should subclinical hypothyroidism be treated?

Usually if TSH >10 mIU/L, during pregnancy, or with positive TPO antibodies.

How is subclinical hyperthyroidism managed in exams?

Observation initially; treat only if persistent or high-risk.

Can acute illness alter TFTs?

Yes. Non-thyroidal illness commonly lowers FT3 and does not require treatment.


Ready to start?

If you can rapidly classify TFT patterns and resist unnecessary treatment, you will score consistently in MRCP Part 1 endocrine questions. This is a high-yield topic where clarity beats complexity.


Sources

 
 
 

Comments

bottom of page