Is long COVID an official medical diagnosis?

Yes. The World Health Organization published a clinical case definition of post-COVID-19 condition in 2022, and it carries its own diagnosis code (U09.9) in the ICD-10 system used in United States medical records. Fishtown Medicine treats it as what it is: a recognized illness with a structured workup.

Do I need a positive COVID test to be diagnosed?

No. The WHO definition includes probable infection, because millions of people, above all in 2020, were infected when testing was scarce or unreliable. A consistent story and timeline is acceptable grounds to begin the workup.

Can a mild infection cause months of illness?

Yes. Long COVID follows mild and moderate infections routinely, and because mild infections are by far the most common kind, most people with long COVID had an initial illness they managed at home. A rough start is not required.

Can the flu or mono do the same thing?

Yes. The Dubbo study followed people after mono, Ross River virus, and Q fever, and 11% met chronic fatigue criteria at 6 months regardless of which infection started it. Post-viral illness is a general phenomenon, and COVID made it common enough that medicine had to pay attention.

Does exercise help or hurt?

It depends on whether post-exertional malaise is present. Without PEM, gradual reconditioning helps most people. With PEM, exercise-first programs backfire and can set patients back weeks. That is why the workup screens for PEM before anyone prescribes effort.

What tests should I ask for?

Heart rate and blood pressure standing over 10 minutes, a full thyroid panel with antibodies, ferritin and iron studies, a blood count, B12 with homocysteine or methylmalonic acid, morning cortisol, glucose and fasting insulin, and a sleep study when sleep is unrefreshing or snoring is in the picture. Bring a written timeline of the infection and your 3 worst symptoms.

Is this the same as chronic fatigue syndrome?

They overlap. When post-viral illness includes PEM, unrefreshing sleep, and cognitive or orthostatic symptoms for more than 6 months, it can meet the 2015 Institute of Medicine criteria for ME/CFS. The label matters less than the plan, and the plan is the same: pace around PEM, find contributors, treat them.

How is POTS formally diagnosed?

By a sustained heart rate increase of at least 30 beats per minute within 10 minutes of standing or head-up tilt, without a significant blood pressure drop, in someone with at least 3 months of orthostatic symptoms and no better explanation. Cardiology or autonomic specialists confirm it with a stand test or tilt-table study. Treatment works well enough that finding it changes lives.

How do I pace without becoming deconditioned?

Pacing means keeping daily effort below the crash threshold, using a symptom diary or heart rate as a guide, and holding activity steady instead of riding boom-and-bust cycles. Deconditioning is a fair concern, and the sequence answers it: stabilize first so crashes stop, then expand activity in small steps that hold. With PEM, stability comes before strength.

Is this anxiety or depression?

Anxiety and depression can arrive with any long illness, and they deserve care in their own right. They do not explain a heart rate that jumps 40 beats on standing, a delayed crash after effort, or thyroid antibodies, and treating mood alone does not resolve those findings. The distinction has its own page: anxiety, or physiology. Both things can be true, and both get treated.

Does vaccination change the risk?

The evidence summarized in the 2023 Nature Reviews Microbiology review suggests vaccination before infection lowers the risk of developing long COVID, though it does not remove it. Each new infection is a fresh roll of the dice, which is a fair reason to keep avoiding infections you can avoid.

Can brain fog be worked up on its own?

Yes. Brain fog in post-viral illness often tracks with the same contributors this workup finds: orthostatic blood flow problems, thyroid disease, low iron, poor sleep. The symptom has its own guide at brain fog, and what is behind it.

Which specialists get involved, and who leads?

Cardiology or autonomic neurology for POTS confirmation, neurology for small fiber testing, pulmonology for lingering breathing symptoms, and sleep medicine when the study is abnormal. The workup fails when 4 specialists each see a normal test and nobody holds the whole story. At Fishtown Medicine, Dr. Ash leads it: every specialist report comes back to him, and he reads every one himself.

What should a first visit for this look like?

A doctor who has already read your timeline, asks about crash patterns and standing tolerance without being prompted, examines you, and leaves with a sequenced plan you can repeat back: which tests, in what order, and what each would change. If you leave a visit with "your labs are fine, try to exercise," you have a second opinion to seek, and your experience deserves one.

Is long COVID an official medical diagnosis?

Yes. The World Health Organization published a clinical case definition of post-COVID-19 condition in 2022, and it carries its own diagnosis code (U09.9) in the ICD-10 system used in United States medical records. Fishtown Medicine treats it as what it is: a recognized illness with a structured workup.

Do I need a positive COVID test to be diagnosed?

No. The WHO definition includes probable infection, because millions of people, above all in 2020, were infected when testing was scarce or unreliable. A consistent story and timeline is acceptable grounds to begin the workup.

Can a mild infection cause months of illness?

Yes. Long COVID follows mild and moderate infections routinely, and because mild infections are by far the most common kind, most people with long COVID had an initial illness they managed at home. A rough start is not required.

Can the flu or mono do the same thing?

Yes. The Dubbo study followed people after mono, Ross River virus, and Q fever, and 11% met chronic fatigue criteria at 6 months regardless of which infection started it. Post-viral illness is a general phenomenon, and COVID made it common enough that medicine had to pay attention.

Does exercise help or hurt?

It depends on whether post-exertional malaise is present. Without PEM, gradual reconditioning helps most people. With PEM, exercise-first programs backfire and can set patients back weeks. That is why the workup screens for PEM before anyone prescribes effort.

What tests should I ask for?

Heart rate and blood pressure standing over 10 minutes, a full thyroid panel with antibodies, ferritin and iron studies, a blood count, B12 with homocysteine or methylmalonic acid, morning cortisol, glucose and fasting insulin, and a sleep study when sleep is unrefreshing or snoring is in the picture. Bring a written timeline of the infection and your 3 worst symptoms.

Is this the same as chronic fatigue syndrome?

They overlap. When post-viral illness includes PEM, unrefreshing sleep, and cognitive or orthostatic symptoms for more than 6 months, it can meet the 2015 Institute of Medicine criteria for ME/CFS. The label matters less than the plan, and the plan is the same: pace around PEM, find contributors, treat them.

How is POTS formally diagnosed?

By a sustained heart rate increase of at least 30 beats per minute within 10 minutes of standing or head-up tilt, without a significant blood pressure drop, in someone with at least 3 months of orthostatic symptoms and no better explanation. Cardiology or autonomic specialists confirm it with a stand test or tilt-table study. Treatment works well enough that finding it changes lives.

How do I pace without becoming deconditioned?

Pacing means keeping daily effort below the crash threshold, using a symptom diary or heart rate as a guide, and holding activity steady instead of riding boom-and-bust cycles. Deconditioning is a fair concern, and the sequence answers it: stabilize first so crashes stop, then expand activity in small steps that hold. With PEM, stability comes before strength.

Is this anxiety or depression?

Anxiety and depression can arrive with any long illness, and they deserve care in their own right. They do not explain a heart rate that jumps 40 beats on standing, a delayed crash after effort, or thyroid antibodies, and treating mood alone does not resolve those findings. The distinction has its own page: anxiety, or physiology. Both things can be true, and both get treated.

Does vaccination change the risk?

The evidence summarized in the 2023 Nature Reviews Microbiology review suggests vaccination before infection lowers the risk of developing long COVID, though it does not remove it. Each new infection is a fresh roll of the dice, which is a fair reason to keep avoiding infections you can avoid.

Can brain fog be worked up on its own?

Yes. Brain fog in post-viral illness often tracks with the same contributors this workup finds: orthostatic blood flow problems, thyroid disease, low iron, poor sleep. The symptom has its own guide at brain fog, and what is behind it.

Which specialists get involved, and who leads?

Cardiology or autonomic neurology for POTS confirmation, neurology for small fiber testing, pulmonology for lingering breathing symptoms, and sleep medicine when the study is abnormal. The workup fails when 4 specialists each see a normal test and nobody holds the whole story. At Fishtown Medicine, Dr. Ash leads it: every specialist report comes back to him, and he reads every one himself.

What should a first visit for this look like?

A doctor who has already read your timeline, asks about crash patterns and standing tolerance without being prompted, examines you, and leaves with a sequenced plan you can repeat back: which tests, in what order, and what each would change. If you leave a visit with "your labs are fine, try to exercise," you have a second opinion to seek, and your experience deserves one.

Long COVID Doctor Philadelphia | Post-Viral Illness Care

TL;DR30-second take

Yes, staying sick for months after an infection is a recognized medical condition, even when standard labs are normal. The World Health Organization defines post-COVID condition as symptoms lasting at least 2 months, beginning about 3 months from the infection. Fishtown Medicine works these cases up for treatable contributors: orthostatic intolerance, thyroid disease, iron deficiency, and sleep disorders.

TL;DR: Some people stay sick for months after an infection like COVID, the flu, or mono. This is a known illness with a name, even when every blood test comes back normal. It is not in your head. If this is you: do not force yourself through the crashes, because rest is part of the treatment. Write down your 3 worst symptoms and what makes them worse. Ask for the checks a standard visit skips: your heart rate lying down and then standing, a full thyroid panel, your iron stores, and a sleep evaluation. Then bring the whole story to a doctor who will read it. Parts of this illness are treatable, and finding those parts is the job.

If you had an infection months ago and never got your health back, and every test since has come back normal, the first thing you should hear from a doctor is that your illness is recognized, named, and studied. Normal labs mean the standard panel was not built to see what you have. That is a testing gap, and the gap has a workup of its own.

Is post-viral illness a recognized diagnosis?

Yes. The World Health Organization published a formal case definition in 2022: symptoms that begin within about 3 months of a SARS-CoV-2 infection, last at least 2 months, and cannot be explained by an alternative diagnosis. Read that last clause again, because it settles the argument you may have been having with the healthcare system: normal test results are built into the definition. Arriving with a folder of normal labs fits the diagnosis. It does not rule it out.

This did not start with COVID. In 2006, Australian researchers followed 253 people from the day of an acute infection, and the infections were deliberately different: mono from Epstein-Barr virus, Ross River virus from mosquito bites, and Q fever from farm animal exposure. At 6 months, 11% met criteria for a chronic fatigue syndrome, and it happened at similar rates across all 3 infections. A virus your neighbor cleared in 2 weeks can leave you sick for a year, and that pattern was documented and published 14 years before anyone said "long COVID."

The scale now is what changed. A 2023 review in Nature Reviews Microbiology estimates long COVID follows at least 10% of SARS-CoV-2 infections, with some 65 million people affected worldwide and more than 200 symptoms described across organ systems.

Why do the tests keep coming back normal?

Because the standard panel measures organ damage, and this illness mostly runs on dysregulation: control systems misfiring while the organs they control test intact. A basic metabolic panel checks your kidneys, your liver, and your electrolytes. A blood count checks for anemia and infection. Those were the right first tests, and they were never designed to catch a heart rate that climbs 40 beats when you stand up, or a crash that arrives 36 hours after you carry groceries up the stairs.

3 systems carry most of what patients feel. The first is the autonomic nervous system, the automatic controls for heart rate, blood pressure, temperature, and digestion; when it misfires, standing up becomes work and hot showers become an ordeal. The second is energy metabolism, which shows up as the crash pattern described below. The third is the small nerve fibers, the thin ones that carry pain and temperature signals and help run the automatic functions; a standard nerve test does not see them, and in a small NIH-linked series of long COVID patients referred for neuropathy evaluation, a majority had at least one objective test confirming a problem there. Each of these has its own tests. None of them is on a routine panel.

What is post-exertional malaise?

Post-exertional malaise, PEM, is a crash that arrives a day or 2 after you do more than your current limit, and it is the most important symptom to identify because it changes the treatment plan. This is different from ordinary tiredness after effort. The crash is delayed, it is out of proportion to what you did, and it can take days to lift. The classic story is paying for a birthday party with a week in bed.

PEM is taken seriously at the highest level of medicine: when the Institute of Medicine rebuilt the diagnostic criteria for myalgic encephalomyelitis / chronic fatigue syndrome in 2015, it made PEM the required hallmark of the diagnosis.

The plan changes because effort itself becomes a dose. If PEM is present, "push through it" advice and aggressive exercise programs make the illness worse, and the first treatment is pacing: deliberately spending less energy than you have, so you stop triggering crashes. Pacing is not permanent rest. It protects your baseline while the workup finds the contributors that can be treated.

Guidance from the Clinic

"I believe patients the first time they tell me. The workup's job is to find which parts of this we can treat, and every normal result narrows where we look next."

What belongs in the workup when everything so far was normal?

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A history read start to finish, and then tests aimed at the systems this illness uses. At Fishtown Medicine the list usually includes:

Heart rate and blood pressure, lying and then standing. Measured lying down, then standing over 10 minutes. A sustained rise of 30 or more beats per minute with typical symptoms points to POTS, postural orthostatic tachycardia syndrome, meaning the reflexes that hold your blood pressure steady on standing are misfiring and your heart races to compensate. POTS is common after COVID: in an early case series of 20 post-COVID patients with autonomic problems, 85% still had symptoms 6 to 8 months out. It matters because it is treatable, with fluids, salt, compression, structured reconditioning, and medication when needed.
A full thyroid panel, with antibodies. A TSH alone can look fine while thyroid antibodies say the gland is under attack. If you have been told "thyroid is normal" from a single number, the fuller picture is in thyroid antibodies with a normal TSH.
Iron stores, and a blood count. Ferritin, the storage form of iron, can run low enough to cause fatigue and brain fog long before anemia appears. Months of tiredness with a normal checkup is a pattern with its own workup, and iron is one of its usual suspects.
B12, checked by function. A B12 blood level can read normal while the vitamin is failing at its job. The follow-through is homocysteine or methylmalonic acid, which show whether B12 is working inside your cells instead of how much is floating in your blood.
Morning cortisol, glucose, and fasting insulin when the story fits, because adrenal and metabolic problems wear a fatigue costume.
A sleep evaluation. Unrefreshing sleep is core to this illness, and sleep apnea can appear or worsen after a serious infection. Snoring, gasping, morning headaches, or a bed partner's report earns a sleep study.

Finding one of these does not dismiss the post-viral illness. It hands you a treatable piece of it, and treating that piece moves your floor up. Most of this list is ordinary bloodwork and measurement, and it can start right away.

How does Fishtown Medicine approach an illness like this?

It starts with time and belief. If you have told this story 10 times already, you should not have to write it an 11th: share what you have the energy for, upload the records you already hold, and once you connect, the practice can request the rest on your behalf so you never repeat yourself again. Dr. Ash reads all of it before you ever talk, so the conversation starts at the interesting part instead of the beginning. The workup above gets sequenced over weeks, the treatable findings get treated, and if PEM is in the picture the plan protects you from crash cycles while that happens. When a finding needs a specialist, like cardiology to confirm POTS or neurology for small fiber testing, the referral goes out with the groundwork already done, and both results come back to Dr. Ash, who reads every one himself.

2 things deserve to be said plainly here. First, there is no single test that proves post-viral illness, and anyone selling you one is ahead of the science. The research on causes, including viral persistence and clotting abnormalities, is active and promising, and it has not yet produced a validated clinical test or an approved treatment aimed at those mechanisms. Second, recovery is usually a series of small gains stacked over months, and progress that looks modest week to week reads as meaningful over a season.

When should lingering symptoms send you to a doctor now?

Some symptoms should not wait for a post-viral workup. Get seen the same day, or in an emergency room, for worsening shortness of breath, chest pain, fainting, new weakness on one side, trouble speaking, unintentional weight loss, drenching night sweats, or fevers that keep returning. Those need answers now, and they are not what this article describes.

For everything else, the 3-month mark in the WHO definition is a reasonable anchor to begin a formal workup. You do not have to wait 3 months to be taken seriously, and if you are already past it, the workup is overdue.

Key Takeaways

Staying sick for months after an infection is a recognized, named illness,

and the WHO definition expects normal standard tests. - Post-viral illness predates COVID: 11% of people met chronic fatigue criteria 6 months after mono, Ross River virus, or Q fever in a 2006 prospective study. - Post-exertional malaise, the delayed crash after effort, is the symptom that changes the plan: pacing first, exercise programs only when PEM is absent. - The productive workup targets systems standard panels skip: heart rate and blood pressure on standing, thyroid with antibodies, iron stores, B12 function, cortisol, and sleep. - Treatable contributors like POTS, thyroid disease, iron deficiency, and sleep apnea are found in a meaningful share of cases, and treating them raises the floor.

Connected your own dots: POTS, MCAS, and hypermobility - when the pattern spans systems and specialists
Tired for months: the fatigue workup - the general version of this investigation
Thyroid antibodies with a normal TSH - the panel behind "your thyroid is fine"
Small fiber neuropathy - the nerve problem standard tests miss

Scientific References

Soriano JB, Murthy S, Marshall JC, Relan P, Diaz JV; WHO Clinical Case Definition Working Group. "A clinical case definition of post-COVID-19 condition by a Delphi consensus." The Lancet Infectious Diseases. 2022;22(4):e102-e107. PubMed
Hickie I, Davenport T, Wakefield D, et al. "Post-infective and chronic fatigue syndromes precipitated by viral and non-viral pathogens: prospective cohort study." BMJ. 2006;333(7568):575. BMJ
Davis HE, McCorkell L, Vogel JM, Topol EJ. "Long COVID: major findings, mechanisms and recommendations." Nature Reviews Microbiology. 2023;21(3):133-146. Nature / PubMed
Institute of Medicine. "Beyond Myalgic Encephalomyelitis/Chronic Fatigue Syndrome: Redefining an Illness." National Academies Press, 2015. Criteria summary: CDC
Oaklander AL, Mills AJ, Kelley M, et al. "Peripheral Neuropathy Evaluations of Patients With Prolonged Long COVID." Neurology Neuroimmunology & Neuroinflammation. 2022;9(3):e1146. Journal
Blitshteyn S, Whitelaw S. "Postural orthostatic tachycardia syndrome (POTS) and other autonomic disorders after COVID-19 infection: a case series of 20 patients." Immunologic Research. 2021;69(2):205-211. Springer

Fishtown Medicine | Symptoms

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Frequently Asked Questions

Common Questions

It varies too much for a fair promise. Many people improve substantially over 3 to 12 months, and a smaller group stays ill longer. What moves the odds: identifying PEM early and pacing instead of pushing, treating every contributor the workup finds, and protecting sleep. Fishtown Medicine measures progress in function, like hours upright per day, because that is what recovery feels like from the inside.

Deep-Dive Questions

It is orthostatic vitals done properly: rest lying down 10 minutes, record heart rate and blood pressure, then stand still and record both at 2, 5, and 10 minutes. A sustained heart rate rise of 30 or more beats per minute in an adult, with symptoms, suggests POTS. A home version with a blood pressure cuff or a wearable is a useful starting record to bring to your visit, and a formal diagnosis still needs clinical confirmation.

The leading hypotheses are viral persistence, meaning fragments or reservoirs of virus lingering in tissue, immune dysregulation and autoimmunity, clotting abnormalities including microclots, and reactivation of older viruses like Epstein-Barr. These are active research programs, and none has yet produced a validated everyday clinical test or an approved targeted treatment. Any clinic selling microclot testing or apheresis as proven care is charging for the hypothesis, and you deserve to know that before paying.

No drug is approved to treat long COVID as a disease yet. What works today is treating the contributors the workup finds, like POTS, thyroid disease, iron deficiency, and sleep apnea, with pacing protecting the baseline. Low-dose naltrexone, an old medication used off-label at a small fraction of its usual dose, is one option Dr. Ash discusses for post-viral fatigue and brain fog when the picture fits; the early studies are small and promising, larger trials are still running, and that evidence grade is part of the conversation before any prescription.

Small fiber neuropathy, damage to the thin nerve fibers that carry pain and temperature and help run automatic functions, has been found on objective testing in a majority of one small referred long COVID series. It can explain burning or prickling sensations and some autonomic symptoms, and it is missed by standard nerve conduction studies. The fuller picture is in the small fiber neuropathy guide.

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