Fatigue in Primary Care

Introduction

Fatigue - persistent tiredness or lack of energy not relieved by rest - is one of the most common presenting symptoms in general practice, reported by a substantial proportion of adults attending at some point, and it accounts for a disproportionate share of consultation time relative to how often it leads to a serious diagnosis.¹

The differential is deliberately broad, spanning physical disease, psychiatric illness, sleep disorders, medication effects and social/lifestyle factors, and a structured history is what actually narrows it - blanket blood tests without a directed history tend to either miss the answer or generate incidental findings that create more work than they resolve.

This is a genuinely difficult symptom to manage well precisely because the base rate of serious disease is low relative to how common the complaint is, which creates a real tension between thorough assessment and proportionate use of investigation and referral - the skill this topic tests is calibrating that balance using the history, not applying a fixed panel of tests to everyone regardless of presentation.

Structured history

• Onset and duration: sudden versus gradual, and how long it has been present - fatigue over 4-6 months lasting despite rest is a different problem from a few weeks of tiredness after a viral illness
• Pattern: constant versus fluctuating, worse at a particular time of day, and whether it improves with rest (favouring a physical or sleep cause) or is present even after adequate rest (raising depression or ME/CFS)
• Post-exertional malaise: specifically ask whether exertion - physical, cognitive or emotional - triggers a delayed, disproportionate worsening, which points towards ME/CFS
• Associated symptoms: weight change, fever, night sweats, breathlessness, palpitations, bowel habit change, menstrual changes, pain, mood symptoms
• Sleep: quantity, quality, snoring, witnessed apnoeas, and whether the patient wakes unrefreshed
• Mood and stress: screen directly for low mood, anhedonia, anxiety and life stressors - do not wait until 'everything else is excluded' to ask
• Medication and substance use: new drugs, alcohol, recreational drug use, and caffeine intake at both extremes
• Functional and occupational impact: what the fatigue actually stops the patient doing, which both gauges severity and guides support
• Social context: caring responsibilities, shift work, financial stress, and sleep-disrupting home circumstances

Assessing sleep in detail

Sleep problems are one of the most common, and most under-explored, contributors to fatigue seen in primary care, partly because a brief "how's your sleep?" question is easy to answer reassuringly without the patient realising their sleep is genuinely disrupted.

• Quantity: total sleep time and whether it matches recommended amounts for age
• Quality: number of awakenings, time to fall asleep, and whether the patient wakes feeling refreshed
• Snoring and witnessed apnoeas: ask the bed partner directly where possible, since the patient themselves is often unaware
• Restless legs or periodic limb movements: an uncomfortable urge to move the legs, worse in the evening and at rest, disrupting sleep onset and continuity
• Sleep environment and habits: screen use before bed, caffeine and alcohol timing, shift patterns, and a chaotic or noisy sleep environment
• Mood and anxiety-related insomnia: difficulty falling or staying asleep driven by rumination or anxiety, which points towards a primary mood disorder rather than a primary sleep disorder

Examination

Often unremarkable, but should be directed by the history and screen broadly for clues:

• General: pallor (anaemia), weight, lymphadenopathy, signs of thyroid disease, jaundice
• Cardiovascular: pulse, blood pressure, signs of heart failure
• Respiratory: signs of chronic lung disease or effusion
• Abdominal: organomegaly, masses
• Neurological: focal deficits, if suggested by the history
• Mental state: affect, engagement, psychomotor changes

First-line investigation

A standard screening panel, guided but not replaced by the history, identifies the majority of organic causes found in primary care:

Further tests are directed by findings - for example, HIV testing where risk factors are present, chest X-ray if respiratory symptoms coexist, or a short synacthen test if adrenal insufficiency is suspected (postural hypotension, hyperpigmentation, hyponatraemia with hyperkalaemia).

Common and important causes

Special populations

The differential and the appropriate threshold for investigation both shift with life stage, and applying an adult, non-pregnant differential uniformly to every patient risks missing the explanation that is actually most likely in a given group.

• Older adults: fatigue may be the presenting feature of frailty, polypharmacy, undiagnosed heart failure, or depression, which is frequently under-recognised in this age group - see ³ for the frailty perspective
• Postnatal women: anaemia, thyroiditis and postnatal depression are all common and should be actively screened for, not attributed automatically to normal new-parent tiredness
• Adolescents: consider mental health, sleep hygiene and, if pattern fits, ME/CFS; be alert to eating disorders, which can present with fatigue
• Shift workers: circadian disruption is a genuine, common and often under-addressed cause, worth naming explicitly rather than defaulting to blood tests alone
• Menstruating women and vegetarians/vegans: higher baseline risk of iron deficiency, worth a lower threshold for checking ferritin even without overt anaemia on the FBC
• Patients with a chronic condition already under specialist follow-up: consider whether fatigue reflects poor control of the known condition (e.g. anaemia of chronic kidney disease, undertreated hypothyroidism) before assuming an entirely new cause

When to consider a formal ME/CFS diagnosis or refer

Most fatigue presenting to primary care resolves, or is explained by an identifiable cause, well within the 3-month window that would prompt consideration of ME/CFS. Where fatigue persists beyond this, has the specific pattern of post-exertional malaise and unrefreshing sleep, and other causes have been reasonably excluded, formal diagnostic criteria and a structured management approach apply.

• Persistent fatigue beyond 3 months, with post-exertional malaise and unrefreshing sleep, and no alternative explanation - consider ME/CFS and its specific management approach
• Fatigue with a strong suspected sleep disorder (loud snoring, witnessed apnoeas, obesity) unresponsive to simple sleep hygiene advice - refer for a sleep study
• Fatigue with a suspected primary mood or anxiety disorder not responding to initial primary care management - consider referral to psychological therapies or mental health services
• Fatigue with any red-flag feature - urgent referral on the relevant pathway (suspected cancer, haematology, endocrinology as appropriate) rather than continued primary care work-up
• Diagnostic uncertainty after a reasonable, proportionate primary care work-up - general medicine or a fatigue clinic referral, where available, rather than repeated re-testing in primary care

Management principles

Management follows from the identified cause where one is found. Where no single cause is identified after a reasonable, proportionate work-up, a constructive approach - similar to the management of medically unexplained symptoms - combines sleep and lifestyle optimisation, review of contributing medication, treatment of any comorbid mood disorder, and safety-netted follow-up, rather than repeated escalating investigation.

Where fatigue is the presenting symptom of an identified condition, treat that condition and then reassess the fatigue specifically rather than assuming it has resolved. A patient whose hypothyroidism is now biochemically controlled but who remains exhausted needs the differential reopened, not a further increase in levothyroxine - persistent fatigue after adequate treatment of the presumed cause is a common way that a second, coexisting contributor is uncovered.

Red flags

Prognosis

Most fatigue presenting to primary care is self-limiting or resolves once the underlying cause (anaemia, thyroid dysfunction, poor sleep, mood disorder) is treated. A minority of patients go on to a chronic fatigue pattern meeting criteria for ME/CFS, and a minority have an underlying serious diagnosis - the role of a structured history and proportionate investigation is to reliably identify that minority without subjecting everyone else to unnecessary testing.

A useful closing principle is that fatigue is a symptom, not a diagnosis, and the consultation is not complete simply because a screening panel has been sent - the patient should leave with either a working explanation and a plan, or a clear, safety-netted plan for what happens if the picture does not improve or changes, in either case with the opportunity to return before the standard review interval if new symptoms emerge.