If a blood clot travels from the leg to the lungs, it can cause a pulmonary embolism.
Possible symptoms include sudden shortness of breath, chest pain that may worsen with breathing, a rapid heartbeat, dizziness, or fainting.
A pulmonary embolism can be life-threatening.
Anyone experiencing sudden unexplained breathing difficulty or chest pain should seek emergency medical care immediately.
Do not wait to see whether the symptoms disappear.
When should symptoms be considered an emergency?
The combination of symptoms matters.
For example, a person who develops one-sided leg swelling together with chest pain or shortness of breath requires immediate emergency assessment.
Similarly, a severe persistent headache accompanied by blurred vision, confusion, or seizures should not be treated as an ordinary headache.
The CDC recommends immediate medical attention for serious symptoms following COVID-19 vaccination, including chest pain, breathing difficulty, and symptoms suggestive of myocarditis or other serious complications.
The safest approach is to describe the symptoms accurately to medical personnel and provide information about any recent vaccination, medications, illnesses, or operations.
Why self-diagnosis can be dangerous
A swollen leg does not automatically mean someone has DVT.
Likewise, a person who has received a COVID-19 vaccine does not automatically have a vaccine-related complication if they develop leg pain.
The same symptom can be associated with several different conditions.
For example, a painful calf could result from:
-
A muscle strain.
-
A sports injury.
-
A skin or soft-tissue infection.
-
A Baker's cyst.
-
Venous insufficiency.
-
Deep vein thrombosis.
These conditions require different treatments.
Taking blood-thinning medication without medical advice can be dangerous, particularly for someone who has an underlying bleeding problem.
That is why professional diagnosis is essential.
Chapter 4: How Doctors Investigate Leg Problems and Possible Blood Clots
When someone arrives at a hospital with unexplained leg swelling or pain, doctors do not rely on a single photograph or one symptom.
They use a combination of medical history, physical examination, blood tests, and imaging.
The purpose is to identify the underlying condition and determine whether immediate treatment is necessary.
Step 1: Reviewing the patient's medical history
The doctor will usually ask when the symptoms began.
Important questions may include:
-
When did the swelling first appear?
-
Is one leg more swollen than the other?
-
Is there pain when walking?
-
Has the patient recently undergone surgery?
-
Has the patient experienced a previous blood clot?
-
Has the patient been immobile for an extended period?
-
Is there a history of cancer or clotting disorders?
-
Has the patient recently received a vaccine?
-
Which vaccine product and dose were administered?
This information helps doctors evaluate possible explanations.
If vaccination occurred recently, the doctor may consider whether the timing and symptoms are consistent with a recognized adverse event.
However, vaccination history is only one part of the investigation.
Step 2: Physical examination
A healthcare professional may compare both legs.
They may assess:
-
Differences in calf circumference.
-
Skin color.
-
Local temperature.
-
Tenderness.
-
Swelling.
-
Visible veins.
-
Signs of infection or injury.
The doctor may also check blood pressure, heart rate, oxygen levels, and other vital signs.
These findings help determine whether additional testing is necessary.
Step 3: Blood tests
Blood tests can provide useful information.
One commonly used test when investigating suspected DVT is the D-dimer test.
D-dimer is a substance produced when the body breaks down blood clots.
An elevated result may indicate that clot formation and breakdown are occurring.
However, a positive D-dimer result does not prove that someone has DVT.
It can also be elevated because of infection, inflammation, pregnancy, surgery, cancer, and other conditions.
A negative result can help exclude DVT in appropriately selected patients when combined with clinical risk assessment.
If doctors suspect TTS, additional blood tests become particularly important.
These may include:
-
Platelet count.
-
Blood clotting tests.
-
Fibrinogen levels.
-
D-dimer levels.
-
Specialized antibody testing.
The results help determine whether the patient has a clotting disorder associated with low platelet levels.
Step 4: Doppler ultrasound
One of the most important examinations for suspected DVT is venous duplex ultrasound.
Unlike an ordinary X-ray, this examination uses sound waves to visualize blood vessels and assess blood flow.
A trained healthcare professional moves an ultrasound probe along the patient's leg.
The examination can help identify whether a deep vein contains a clot.
One important feature is vein compressibility.
A healthy vein usually collapses when gentle pressure is applied with the ultrasound probe.
A vein containing a significant clot may not compress normally.
Doctors interpret these findings alongside the patient's symptoms and medical history.
The procedure is generally painless, does not use ionizing radiation, and does not require needles.
The Society for Vascular Surgery identifies duplex ultrasound as an important noninvasive method for evaluating blood flow and detecting abnormalities in arteries and veins.
Society for Vascular Surgery+1
Step 5: Why an X-ray may not be enough
The supplied photograph focuses heavily on an X-ray.
However, an ordinary X-ray is not the preferred examination for identifying a clot inside a deep leg vein.
X-rays are more useful for evaluating bone structures and certain surrounding abnormalities.
If a doctor suspects DVT, a venous ultrasound is generally much more appropriate.
Other imaging techniques, such as CT or MRI, may be used when doctors need additional information about particular complications.
The choice depends on the patient's condition.
Step 6: Investigating suspected TTS
When a patient has symptoms suggesting TTS after receiving a vaccine associated with this rare complication, doctors may investigate the platelet count, clotting abnormalities, and specific antibodies.
The PF4 antibody test is one important component of the investigation.
A diagnosis cannot be established merely because someone reports a blood clot after vaccination.
Medical professionals must examine the clinical findings and laboratory evidence.
The WHO has published dedicated clinical guidance for evaluating and managing suspected TTS following COVID-19 vaccination.
World Health Organization+1
Step 7: Treatment depends on the diagnosis
Treatment is not the same for every circulation problem.