Ajax Harwood Clinic

Long COVID: should I be tested?

Last reviewed 2026-09-23Content v349e1a3bd783

Reference tool — not medical advice. Clinician judgement always required.

Post-COVID condition (long COVID)

Clinical diagnosis — no single test

Also called: long COVID, post-COVID-19 condition, long-haul COVID, PASC, chronic COVID, post-acute sequelae of COVID-19

Patients raise long COVID after weeks or months of fatigue, breathlessness, or brain fog following a COVID-19 infection, sometimes confirmed by a positive test at the time and sometimes only suspected. Media coverage, patient support groups, and an ND or physiotherapist noting a link to a past infection all bring the label forward. The persisting symptoms are real and can be disabling; the challenge is that there is no test that confirms the diagnosis, and many of the same symptoms have other, sometimes more treatable, explanations.

Raises suspicion

• New or ongoing symptoms 4 weeks or more after the start of acute COVID-19, which is NICE's threshold for starting an assessment [2]
• Symptoms, commonly fatigue, breathlessness, or cognitive dysfunction, that began within about 3 months of probable or confirmed SARS-CoV-2 infection and have lasted at least 2 months, with no better explanation, which is the WHO clinical case definition [1]
• Symptoms that fluctuate or relapse over time, or that clearly impair daily functioning, work, or school

Does not raise suspicion

• A few weeks of tiredness immediately after a COVID-19 infection, while still in the expected recovery window
• Vague symptoms with no clear timing relative to a COVID-19 infection

Red flags

• New or worsening chest pain
• New or worsening shortness of breath
• Palpitations with syncope (fainting)

Who to test

Persistent symptoms after COVID-19 meeting the WHO or NICE time criteriaNo test confirms post-COVID condition; it is a clinical diagnosis made from history and symptom timing, with testing aimed at excluding alternative or complicating diagnoses [3, 1].
Persistent fatigue or breathlessness after COVID-19: Complete blood count (CBC) (Situation-specific), TSH (thyroid stimulating hormone) (Standard), Ferritin (Standard), Kidney function (creatinine/eGFR, BUN, urine albumin-to-creatinine ratio) (Situation-specific), Electrolytes (sodium, potassium, chloride, bicarbonate) (Situation-specific), HbA1c and fasting glucose (diabetes screening) (Situation-specific)A standard basic fatigue work-up to exclude alternative explanations (anemia, thyroid disease, iron deficiency, kidney disease, diabetes); not specific to long COVID.
New chest pain, dyspnea, or palpitations with syncope: BNP / NT-proBNP (natriuretic peptides) (Standard)Plus ECG and imaging as directed (no TestSelect entry for ECG or CT pulmonary angiogram) to exclude myocarditis, pulmonary embolism, or another cardiac cause before attributing symptoms to long COVID.
Persistent post-exertional malaise (a crash in function after even mild activity) as the dominant featureSubstantial overlap with myalgic encephalomyelitis/chronic fatigue syndrome; see the chronic-fatigue-syndrome tool's 'should I be tested' section for that work-up.

More likely instead

• deconditioning
• ME/CFS (major overlap, especially with post-exertional malaise)
• Depression
• Sleep & insomnia
• Sleep apnea
• Iron deficiency without anemia
• Hypothyroidism (see the thyroid page)

Counselling script

“If your symptoms began within a few months of a COVID-19 infection, have lasted at least two months, and aren't better explained by something else, long COVID is a reasonable working diagnosis, even without a positive test at the time. There's no test that confirms it, so we use blood work and, if needed, other tests to rule out common alternative or contributing causes. If you have new chest pain, breathlessness, or fainting with palpitations, we need to check your heart and lungs first.”

Chart snippet (OSCAR-safe plain text)

Concern discussed, not tested

Concern re: long COVID (post-COVID-19 condition) discussed, raised by patient or ND.
Discriminating features: symptom timing relative to COVID-19 infection, duration, functional impact; reviewed.
Assessment: no test confirms or excludes post-COVID condition; diagnosis is clinical.
Plan: alternative and contributing diagnoses discussed; basic bloodwork considered.
Ref: WHO Delphi clinical case definition of post-COVID-19 condition 2022; NICE NG188.
Patient given info page: https://long-covid.ajaxharwoodclinic.com/patient
Revisit if: new chest pain, breathlessness, or fainting with palpitations develop.

Testing ordered

Concern re: long COVID discussed.
Discriminating features: symptoms began within about 3 months of COVID-19 infection, lasting at least 2 months, no better explanation identified.
Assessment: findings consistent with post-COVID condition; alternative diagnoses being excluded.
Plan: CBC, TSH, ferritin, kidney function, electrolytes and A1C/glucose ordered.
Ref: WHO Delphi clinical case definition of post-COVID-19 condition 2022; Public Health Agency of Canada long COVID page.
Patient given info page: https://long-covid.ajaxharwoodclinic.com/patient
Revisit if: symptoms persist beyond 12 months, worsen, or red-flag features develop.

Revisit if

• New or worsening chest pain, breathlessness, or fainting with palpitations
• Symptoms persisting or worsening beyond 12 months
• Post-exertional malaise becomes the dominant feature (reassess for ME/CFS)

References

1. WHO Clinical Case Definition Working Group (Soriano et al.). A clinical case definition of post-COVID-19 condition by a Delphi consensus (2022)WHO Delphi consensus clinical case definition: symptoms beginning within about 3 months of infection, lasting at least 2 months, with no other explanation
2. NICE / SIGN / RCGP. COVID-19 rapid guideline: managing the long-term effects of COVID-19 (NG188) (2020)NICE defines the trigger for assessment as new or ongoing symptoms 4 weeks or more after acute COVID-19
3. Public Health Agency of Canada. Post COVID-19 condition (long COVID): Symptoms and treatment (2026)There is no single definitive test to diagnose long COVID

Evidence notes

Tag rationale: B, not borderline. Both the WHO Delphi consensus [1] and NICE NG188 [2] define post-COVID condition/long COVID by symptom pattern and timing rather than a biomarker, and PHAC states plainly there is no single definitive test [3]. NICE's 4-week threshold for starting assessment and the WHO's roughly 3-month-onset/2-month-duration threshold for the settled diagnosis are not identical; this record uses NICE's earlier threshold to prompt initial assessment and the WHO definition for the settled diagnosis, and that distinction is worth the reviewer's eye. The Lancet Infectious Diseases fulltext for the WHO definition returned HTTP 403 to automated fetch this session; the quoted definition was confirmed via the PubMed/eutils abstract instead. Post-exertional malaise is flagged as a major overlap with chronic-fatigue-syndrome per the batch notes; this record does not attempt to fully differentiate the two, since the existing chronic-fatigue-syndrome tool is the intended home for that overlap once it adds its own 'should I be tested' section, per the brief.

General clinical reference for Ajax Harwood Clinic. Not medical advice, and not a substitute for individualized clinical assessment.