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Ask Rezzy/Tiredness and fatigue: systematic approach, blood tests and common causes

Tiredness and fatigue: systematic approach, blood tests and common causes

RezzyRezzy

Oh, the classic "Tired All The Time" (TATT) presentation! It's basically the bread and butter of GP rotations and a favorite for the AKT because the differential is so wide. It can be anything from "too many late-night study sessions" to something more serious, so having a solid framework is key.

A Systematic Approach

When a patient presents with fatigue, I like to break it down into three main buckets: Psychological, Physiological, and Physical.

  1. History is King:

    • Duration and Onset: Is this new, or has it been months?
    • Sleep Hygiene: Are they actually sleeping? Check for Obstructive Sleep Apnoea (OSA) symptoms like snoring or waking up gasping.
    • Mood: Depression is one of the most common causes of fatigue. Don't forget to screen with PHQ-9 questions.
    • Red Flags: This is high-yield for the AKT! Always ask about unintentional weight loss, night sweats, lymphadenopathy, or change in bowel habits.

  2. Examination:

    • Look for pallor (anemia), tachycardia, thyroid enlargement, or lymphadenopathy.
    • Check for signs of heart failure or chronic lung disease if they mention breathlessness.

Common Causes

To help you visualize the most likely culprits, I've put together a quick comparison table of the common causes you'll encounter in exams and clinical practice.

[tool call: show_markdown_to_user] Thinking Process: Preparing a comparison table of common causes of fatigue for a UK medical student. Title: Common Causes of Fatigue Content Type: table Markdown:

CauseKey Clinical FeaturesHigh-Yield Fact
Iron Deficiency AnemiaPallor, pica, koilonychia (rare)Most common cause of microcytic anemia.
HypothyroidismWeight gain, cold intolerance, bradycardiaCheck TSH first; T4 is secondary.
DepressionLow mood, anhedonia, sleep disturbanceFatigue is often worse in the morning.
Diabetes MellitusPolyuria, polydipsia, weight lossHbA1c $\ge$ 48 mmol/mol is diagnostic.
Coeliac DiseaseBloating, diarrhea, weight lossCan cause fatigue without GI symptoms.
OSADaytime somnolence, loud snoringAssociated with obesity and a thick neck.
Chronic Fatigue SyndromeFatigue >4 months, post-exertional malaiseA diagnosis of exclusion.

The "TATT" Blood Screen

In the UK, we usually run a standard "fatigue screen" if the history doesn't point to an obvious cause. Here’s what you should be ordering:

  • Full Blood Count (FBC): Looking for anemia or signs of infection/malignancy.
  • Urea & Electrolytes (U&Es): Checking for renal failure or electrolyte imbalances (like hyponatremia).
  • Liver Function Tests (LFTs): Chronic liver disease can be very sneaky.
  • Thyroid Function Tests (TFTs): Specifically looking for hypothyroidism.
  • HbA1c: To rule out Type 2 Diabetes.
  • Ferritin: Crucial! Patients can be iron deficient (and tired) even if their hemoglobin is still in the normal range.
  • ESR/CRP: Non-specific markers of inflammation or occult malignancy.
  • Coeliac Serology (IgA tTG): NICE recommends screening for Coeliac in patients with unexplained fatigue.
  • Bone Profile: Looking for hypercalcemia (the "moans, stones, and groans").

I'll pull up some lessons that go deeper into these differentials and the management of Chronic Fatigue Syndrome, which is a hot topic for the UKMLA.

[tool call: get_related_lessons_by_search_query] Thinking Process: Searching for lessons on fatigue, anemia, and hypothyroidism for AKT revision. Title: Fatigue and TATT Lessons Description: tiredness and fatigue systematic approach, anemia, hypothyroidism, and chronic fatigue syndrome management.

To help you lock this in for your revision, I've also found some flashcards that cover the high-yield diagnostic criteria and "must-know" blood results.

[tool call: get_related_flashcards] Thinking Process: Finding flashcards for fatigue differentials and investigations. Title: Fatigue Revision Cards Search Queries: ["fatigue differentials", "anemia investigations", "hypothyroidism AKT", "coeliac disease screen"] Card Type: premade Page Num: 1 Page Size: 10

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