Understanding the concept of 'diagnostic uncertainty' in managing undifferentiated symptoms in primary care involves recognizing that certain presentations cannot be immediately diagnosed. Which of the following statements best describes the evidence-based approach to managing diagnostic uncertainty?

Safety-netting with clear instructions for re-consultation if symptoms persist, worsen, or new features develop is an essential component of managing uncertainty

Immediate referral to secondary care is always appropriate when a diagnosis cannot be made in primary care to ensure patient safety

Extensive investigation should be undertaken immediately to exclude all possible serious diagnoses before adopting a watch-and-wait approach

Patients should be reassured that the absence of abnormal findings on initial tests means serious pathology is excluded and no follow-up is needed

Empirical treatment should be started for the most likely diagnosis to avoid delays in management

A 35-year-old woman presents with a 10-week history of severe fatigue, aching limbs, and subjective fever. She works as a veterinary nurse. She reports a flu-like illness that never fully resolved. Examination shows temperature 37.8°C, no rash or lymphadenopathy. Blood tests show: Hb 128 g/L, WCC 3.8 × 10⁹/L (lymphocytes 1.2 × 10⁹/L), platelets 156 × 10⁹/L, CRP 12 mg/L, ALT 124 U/L, AST 96 U/L. Blood film shows atypical lymphocytes. Monospot test is negative. What is the most appropriate next investigation?

Serology for Coxiella burnetii (Q fever)

A 66-year-old man with a 15-week history of fatigue and 8kg weight loss has been investigated extensively in primary care. Blood tests including FBC, U&E, LFT, TFT, calcium, glucose, CRP, and PSA are normal. Chest X-ray and abdominal ultrasound are unremarkable. He has no specific symptoms beyond fatigue and weight loss. His appetite is reduced but he has no dysphagia. He is a lifelong non-smoker. What is the most appropriate next step in management?

Request CT chest, abdomen and pelvis with contrast

Arrange colonoscopy under routine pathway as he is >60 years

Arrange urgent upper GI endoscopy under 2-week wait pathway

Refer to general surgery under 2-week wait for further assessment

Reassure and arrange review in 4 weeks with repeat blood tests

A 41-year-old woman presents with a 15-week history of fatigue and 5kg weight loss. She reports heat intolerance and palpitations. Her grandmother had 'thyroid problems'. Examination shows pulse 96 bpm regular, BP 138/72 mmHg, fine tremor, and a smooth thyroid gland enlarged to twice normal size with an audible bruit. Blood tests show: TSH <0.01 mU/L, free T4 42 pmol/L, free T3 12.8 pmol/L. TSH receptor antibodies are strongly positive. What is the most important counselling point before initiating definitive treatment?

She must use reliable contraception and avoid pregnancy during and for 6 months after radioiodine treatment

Carbimazole may cause agranulocytosis and she should seek urgent medical attention if she develops a sore throat or fever

Radioiodine treatment is contraindicated in women of childbearing age due to long-term fertility effects

Thyroid surgery carries a high risk of recurrent laryngeal nerve damage causing permanent voice changes

Propranolol should not be used if she has a history of asthma or COPD

A 62-year-old man presents with an 11-week history of intermittent fevers up to 38.6°C, night sweats, and 7kg weight loss. He has a 35-year history of Crohn's disease managed with adalimumab. Examination shows temperature 38.2°C, no lymphadenopathy, chest clear, abdomen soft with no masses. Blood tests show: Hb 102 g/L, WCC 11.2 × 10⁹/L, neutrophils 8.4 × 10⁹/L, CRP 78 mg/L. Chest X-ray is normal. Three sets of blood cultures are negative. What is the most appropriate next investigation?

CT chest, abdomen and pelvis with contrast

Colonoscopy with multiple biopsies

Faecal calprotectin and Crohn's disease activity index

Interferon-gamma release assay (IGRA) for tuberculosis

A 48-year-old woman presents with a 16-week history of severe fatigue, widespread pain, and 4kg weight loss. She scores 7/10 on a pain scale and reports poor sleep with frequent waking. Examination shows multiple tender points on palpation but no synovitis or muscle weakness. Blood tests show: Hb 118 g/L, WCC 6.2 × 10⁹/L, ESR 8 mm/hr, CRP 3 mg/L, TSH 2.4 mU/L, calcium 2.38 mmol/L, vitamin D 28 nmol/L. She meets fibromyalgia diagnostic criteria. What feature most strongly suggests an alternative or additional diagnosis requires investigation?

The presence of unintentional weight loss

The elevated ESR relative to normal CRP

The severity of fatigue and sleep disturbance

The widespread pain with multiple tender points

A 39-year-old man presents with a 12-week history of fever occurring every 48 hours, peaking at 39.5°C, with associated rigors and sweating. Between episodes he feels completely well. He returned from a 6-month work assignment in Nigeria 10 months ago. He took malaria prophylaxis irregularly. Examination during a febrile episode shows temperature 39.4°C, pulse 108 bpm, BP 126/78 mmHg, mild splenomegaly. Three blood films taken during afebrile periods were negative for malaria parasites. What is the most appropriate next step?

Repeat thick and thin blood films during a febrile episode

Perform malaria rapid diagnostic test (RDT) immediately

Request serology for Plasmodium vivax and ovale antibodies

Arrange bone marrow aspiration for malaria detection

Start empirical treatment with artemether-lumefantrine

A 57-year-old woman presents with a 13-week history of fatigue and 6kg weight loss. She has developed a sensation of fullness after small meals. Her only medication is levothyroxine 100mcg for hypothyroidism. Examination reveals a palpable spleen 4cm below the left costal margin. Blood tests show: Hb 142 g/L, WCC 68 × 10⁹/L (neutrophils 52 × 10⁹/L, lymphocytes 4 × 10⁹/L, eosinophils 3 × 10⁹/L, basophils 5 × 10⁹/L, myelocytes 4 × 10⁹/L), platelets 528 × 10⁹/L. Blood film shows a full spectrum of myeloid cells. What is the most appropriate immediate management?

Urgent referral to haematology for suspected chronic myeloid leukaemia within 48 hours

Arrange bone marrow biopsy in primary care before referral

Start prophylactic allopurinol and arrange routine haematology referral

Prescribe hydroxycarbamide and refer to haematology within 2 weeks

Admit to hospital immediately due to hyperleukocytosis risk

A 53-year-old woman presents with a 14-week history of progressive fatigue, 8kg weight loss, and intermittent abdominal discomfort. She has a history of coeliac disease diagnosed 12 years ago and reports good dietary compliance. Examination shows conjunctival pallor and mild generalised lymphadenopathy with 1cm nodes in cervical and axillary regions. Blood tests show: Hb 94 g/L, MCV 78 fL, WCC 3.2 × 10⁹/L, platelets 142 × 10⁹/L, ferritin 8 μg/L, tissue transglutaminase IgA antibodies negative, IgA level normal. What is the most likely diagnosis?

Non-Hodgkin lymphoma (enteropathy-associated T-cell lymphoma)

Refractory coeliac disease type II

Giardiasis causing malabsorption

Progression to ulcerative jejunoileitis

Which of the following best describes the 'Pettersson criteria' used in the systematic assessment of prolonged fever in primary care?

A structured framework requiring fever >38.3°C for >3 weeks, multiple outpatient assessments, and failure of empirical antibiotic therapy

A mnemonic-based approach categorizing causes into Infectious, Inflammatory, Iatrogenic, and Neoplastic categories

A scoring system that risk-stratifies patients based on age, comorbidities, and fever characteristics to determine need for hospital admission

A diagnostic protocol mandating specific investigations in sequence: blood cultures, imaging, then invasive procedures

A patient-reported outcome measure assessing fever impact on quality of life and functional capacity

Fever of unknown origin for UKMLA AKT: High-Yield General Practice & Primary Care Lessons

Quick Overview

Fever of Unknown Origin (FUO) is defined as temperature >38.3°C on multiple occasions, persisting for >3 weeks, with no diagnosis after initial investigations (including history, examination, and basic tests). Represents a diagnostic challenge requiring systematic evaluation. NICE NG51 emphasizes antimicrobial stewardship-avoid empirical antibiotics without clear indication, as this masks underlying pathology.

Core Facts & Concepts

Classic FUO Criteria (Petersdorf & Beeson):

Temperature >38.3°C (101°F)
Duration >3 weeks
No diagnosis after 1 week of inpatient investigation (modern: 3 outpatient visits or 3 days inpatient)

FUO Categories:

Category	Definition	Common Causes
Classic	Community-acquired, immunocompetent	Infections (30-40%), malignancy (20-30%), inflammatory (10-20%)
Nosocomial	Hospitalized ≥24h, not incubating on admission	C. difficile, UTI, surgical complications, VTE
Neutropenic	Neutrophils <500/μL	Fungal infections (Aspergillus, Candida), bacterial sepsis
HIV-associated	HIV-positive with fever >3 weeks	TB, MAC, CMV, lymphoma, PCP

📊 Cause Distribution (Classic FUO):

Infections: 30-40% (TB, endocarditis, abscesses, EBV, CMV)
Malignancy: 20-30% (lymphoma, renal cell carcinoma, hepatocellular carcinoma)
Inflammatory: 10-20% (giant cell arteritis, Still's disease, SLE, vasculitis)
Miscellaneous: 10-20% (drug fever, factitious, VTE)
Undiagnosed: 10-15% (often resolves spontaneously)

Figure 1: Chest X-ray showing bilateral hilar lymphadenopathy in sarcoidosis

⚠️ Warning: NICE NG51-do NOT prescribe empirical antibiotics for FUO without microbiological evidence or clear focus. This delays diagnosis and promotes resistance.

Problem-Solving Approach

Structured Investigation Pathway:

Detailed History (30% diagnostic yield)
- Travel (malaria, typhoid, brucellosis)
- Animal exposure (Q fever, brucellosis, leptospirosis)
- Occupation (healthcare-TB; farming-brucellosis)
- Medications (drug fever typically 7-10 days after starting)
- Sexual history (HIV, syphilis)
Repeated Examination
- Daily temperature chart (pattern recognition)
- New murmur → endocarditis
- Temporal artery tenderness → GCA (age >50)
- Lymphadenopathy → lymphoma, TB
First-Line Investigations
- FBC (neutrophilia, lymphopenia, pancytopenia)
- CRP/ESR (ESR >100 suggests GCA, malignancy, abscess)
- Blood cultures × 3 (before antibiotics)
- Urinalysis + culture
- CXR (TB, lymphoma, malignancy)
- LFTs (hepatobiliary sepsis, lymphoma)
Second-Line Investigations (if first-line negative)
- CT chest/abdomen/pelvis with contrast (abscess, lymphoma, malignancy)
- Echocardiography (TTE then TOE if endocarditis suspected)
- Autoantibodies (ANA, ANCA, RF if inflammatory suspected)
- HIV test (with consent)
- Mantoux/IGRA (TB)
Specialist Investigations
- PET-CT (malignancy, vasculitis, infection foci-80% sensitivity)
- Temporal artery biopsy (GCA-do NOT delay if suspected)
- Bone marrow biopsy (lymphoma, TB, leishmaniasis)
- Tissue biopsy of any accessible lesion

Figure 2: PET-CT scan showing increased FDG uptake in large vessel vasculitis

🚩 Red Flags for Urgent Referral:

Age >50 + ESR >100 + headache/jaw claudication → same-day rheumatology (GCA)
New murmur + fever → same-day cardiology (endocarditis)
Weight loss + night sweats → 2-week-wait haematology (lymphoma)
Neutropenic fever → immediate hospital admission

Analysis Framework

Discriminating Features:

Feature	Infectious	Malignancy	Inflammatory	Drug Fever
Onset	Acute/subacute	Insidious	Variable	7-10 days post-drug
Pattern	Continuous/intermittent	Low-grade persistent	Intermittent	Continuous
Night sweats	+++ (TB, lymphoma)	+++	+	-
Weight loss	++	+++	++	-
Rash	Variable	Rare	++ (SLE, vasculitis)	+++ (maculopapular)
ESR	↑↑	↑↑↑	↑↑↑	Normal/↑
CRP	↑↑↑	↑↑	↑↑↑	Normal/↑

📌 Remember: FEVER - Factitious, Endocarditis, Vasculitis, Emboli (PE), Real oddities (Still's, drug fever)

NICE NG51 Antimicrobial Stewardship:

No antibiotics without microbiological diagnosis or clear sepsis
If critically unwell: take cultures first, then targeted therapy
Review diagnosis if no response in 48-72 hours

Visual Aid

Common Causes by Age:

Age Group	Top 3 Causes
<35 years	TB, HIV, Still's disease
35-65 years	Endocarditis, lymphoma, abscess
>65 years	GCA, malignancy, endocarditis

Key Points Summary

✓ FUO Definition: Temperature >38.3°C for >3 weeks, no diagnosis after initial investigations-requires systematic approach

✓ Cause Distribution: Infections (30-40%), malignancy (20-30%), inflammatory (10-20%)-but 10-15% remain undiagnosed

✓ History is Diagnostic: Travel, animals, occupation, medications account for 30% of diagnoses-repeat examination daily

✓ ESR >100 mm/hr: Think GCA (age >50), malignancy, or abscess-temporal artery biopsy if suspected

✓ NICE NG51 Key: NO empirical antibiotics without clear indication-masks diagnosis and promotes resistance

✓ PET-CT: 80% sensitivity for occult malignancy, vasculitis, and infection foci-consider if CT negative

✓ Red Flags: New murmur (endocarditis), age >50 + headache + ESR >100 (GCA), neutropenic fever (immediate admission)

Continue reading on Oncourse

CONTINUE READING — FREE

or get the app

App Store|Google Play