For many people, COVID-19 does not end when the initial infection clears. Weeks or even months after testing negative, some individuals continue to experience fatigue, brain fog, shortness of breath, chest discomfort, and a range of other symptoms that can make daily life genuinely difficult. This condition — broadly called long COVID, or post-acute sequelae of SARS-CoV-2 (PASC) — is recognized by the CDC and major health organizations as a real and serious medical condition.
If you or someone you love is navigating long COVID, this guide offers a practical starting point: understanding which tests clinicians commonly use, how to read and contextualize oxygen levels at home, what warning signs require urgent attention, and how to build a care plan that actually works for your situation.
What Is Long COVID, Exactly?
Long COVID is an umbrella term for symptoms that persist or newly appear at least four weeks after an acute COVID-19 infection. Researchers believe it involves a combination of factors that may vary from person to person — including ongoing immune activation, small-vessel damage, disruptions to the autonomic nervous system, and in some cases viral remnants persisting in tissues. Because the underlying mechanisms are still being studied, there is no single test that diagnoses long COVID. Instead, clinicians piece together a picture using your symptom history, physical exam findings, and targeted testing to rule out other causes and identify treatable complications.
Common long COVID symptoms include:
- Fatigue that is disproportionate to activity and does not improve with rest
- Post-exertional malaise — a worsening of symptoms after physical or mental effort
- Cognitive difficulties often described as brain fog, memory lapses, or trouble concentrating
- Shortness of breath or chest tightness, even at rest or with mild activity
- Heart palpitations or a racing pulse
- Sleep disruption, headaches, and mood changes
- Joint or muscle pain
This list is not exhaustive. Long COVID can affect nearly every organ system, which is part of what makes it so challenging to diagnose and treat.
Tests Your Clinician May Order
Because long COVID mimics — and sometimes overlaps with — other conditions, a good workup is about ruling things in and out systematically. Here is a plain-language breakdown of tests that commonly come up in long COVID evaluations.
Basic blood panels. A complete blood count (CBC) checks whether your red blood cells, white blood cells, and platelets are in normal ranges. An abnormal result might point to anemia, which can explain fatigue and breathlessness, or to ongoing inflammation. A comprehensive metabolic panel looks at kidney function, liver enzymes, blood sugar, and electrolytes. These are often the starting point before anything more specialized.
Inflammatory markers. Tests like C-reactive protein (CRP) and erythrocyte sedimentation rate (ESR) can indicate whether inflammation is still elevated. Some long COVID patients have normal inflammatory markers despite significant symptoms, which researchers think may reflect localized rather than systemic inflammation.
Thyroid function. Thyroid disorders can cause fatigue, brain fog, and heart palpitations — symptoms that overlap substantially with long COVID. A TSH (thyroid-stimulating hormone) test is a routine and important step.
Cardiac evaluation. If you have chest pain, palpitations, or shortness of breath, your clinician may order an electrocardiogram (EKG or ECG) to look at your heart's electrical activity, and possibly an echocardiogram (heart ultrasound) to evaluate heart structure and pumping function. Some long COVID patients develop a condition called myocarditis (inflammation of the heart muscle) or pericarditis (inflammation of the sac around the heart), which requires prompt attention.
Pulmonary function tests (PFTs). These breathing tests measure how much air your lungs can hold and how efficiently you can move air in and out. They can detect restrictive or obstructive lung patterns that may explain persistent shortness of breath.
Autonomic testing. Dysautonomia — a disruption of the autonomic nervous system that controls heart rate, blood pressure, and other automatic functions — has been identified in a meaningful subset of long COVID patients. A tilt-table test or active stand test (measuring heart rate and blood pressure when you go from lying to standing) may be recommended if you experience dizziness, rapid heartbeat upon standing, or fainting.
Neuropsychological assessment. For those with significant cognitive symptoms, a formal neuropsychological evaluation can document the nature and extent of difficulties and guide rehabilitation strategies.
Your clinician may not order all of these at once. Testing is typically guided by your specific symptom profile and what earlier results reveal.
Understanding Oxygen Readings at Home
Pulse oximeters — the small clip-on devices that measure blood oxygen saturation (SpO2) — became household items during the pandemic, and many long COVID patients use them to monitor themselves between appointments. Knowing how to interpret the readings is important, both to avoid unnecessary anxiety and to recognize when a reading warrants action.
What the numbers mean. A healthy SpO2 reading at sea level is generally considered to be between 95% and 100%. Readings between 92% and 94% may be a sign that your lungs or circulation are not working as efficiently as they should, and readings below 92% are generally treated as a medical concern requiring prompt evaluation.
Important caveats about home pulse oximeters. Consumer-grade devices are not as accurate as medical-grade equipment, and their accuracy can be affected by cold hands, nail polish, poor circulation, and — as research has documented — skin pigmentation. Studies have found that pulse oximeters can overestimate oxygen levels in people with darker skin tones, meaning the device may show a normal reading when the true level is lower. If you have concerns about your oxygen levels and you have darker skin, share this limitation explicitly with your clinician.
Watching trends, not just single readings. One reading in isolation is less meaningful than a pattern over time. Keep a simple log: note the reading, the time of day, whether you were at rest or had just exerted yourself, and how you felt. This log becomes valuable information for your care team.
The exertion test — use with caution. Some providers ask patients to check their oxygen before and after a brief walk to see whether it drops significantly with activity (a phenomenon called exertional desaturation). However, if you are experiencing significant post-exertional malaise, pushing yourself to exert beyond your comfortable range can trigger symptom flares. Discuss any at-home exertion testing with your clinician before trying it.
Warning Signs That Need Urgent Attention
Long COVID is a chronic, evolving condition — but some symptoms signal an emergency. Do not wait for a scheduled appointment if you experience:
- Severe shortness of breath or difficulty breathing at rest
- Chest pain or pressure, especially if it radiates to your arm, jaw, or back
- A pulse oximeter reading below 92%, especially if accompanied by breathlessness or confusion
- Rapid or irregular heartbeat that is new or significantly worse
- Sudden confusion, difficulty speaking, facial drooping, or weakness on one side of the body
- Fainting or near-fainting
Call emergency services or go to an emergency room for any of the above. Long COVID does not protect you from other serious conditions — heart attacks, blood clots, and strokes require immediate care.
Building a Long COVID Action Plan
One of the most effective things you can do for long COVID — alongside any specific treatments — is to build a structured, written action plan with your care team. Here is how to approach it.
Establish a primary point of contact. Ideally, one clinician coordinates your care, even if you are seeing multiple specialists. This might be your primary care provider, or a clinician at a dedicated long COVID clinic if one is available in your area.
Keep a symptom diary. Track your symptoms, energy levels, sleep, oxygen readings if relevant, and any triggers you notice. Many patients find that patterns emerge over weeks — certain activities, times of day, or stressors that reliably worsen symptoms. This information helps your care team make better decisions and helps you pace yourself.
Learn about pacing. For many long COVID patients — particularly those with post-exertional malaise — the instinct to push through fatigue can backfire and cause multi-day symptom crashes. A strategy called pacing, which involves staying within your current energy envelope rather than exceeding it, is widely recommended by long COVID specialists and patient advocates. Ask your care team about working with an occupational therapist experienced in energy conservation.
Know your green, yellow, and red zones. Think of your symptoms in traffic-light terms. Green is your baseline — manageable symptoms, reasonable function. Yellow means something has changed and you should rest, reduce activity, and monitor closely. Red means you need to contact your clinician or seek emergency care. Write down what each zone looks like for you personally and share it with someone in your household.
Mental health is part of the plan. Living with a poorly understood chronic condition is emotionally exhausting. Anxiety, depression, and grief over lost function are common in long COVID patients and are not signs of weakness. Ask your care team about referrals to mental health support, and consider connecting with a peer support group — many long COVID patients find significant comfort in communities of others who truly understand their experience.
A Note on Evolving Research
Long COVID research is moving quickly. Clinical trials are underway exploring various treatments, and what clinicians recommend may shift as new evidence emerges. This guide reflects current, broadly accepted guidance — but it is not a substitute for a conversation with a clinician who knows your specific medical history. If something in your situation feels urgent or confusing, reach out to your care team. You deserve to be heard, and you deserve care that takes your symptoms seriously.