A coughed-up blood clot from the lungs typically appears as a small, dark-red or maroon lump embedded in mucus, sometimes with visible strands of phlegm running through it. The material can range from bright red streaks on otherwise clear sputum to solid, rubbery masses that hold a distinct shape. In rarer cases, people cough up startlingly large, branching structures that look like casts of their airways. What you see depends on where the bleeding originates, how fast it is occurring, and how long the blood sat in the lungs before being expelled.
Color, Texture, and Size
Most people who cough up blood are not producing neatly formed clots. Far more often, the material is a mix of blood and mucus, sometimes described as “blood-tinged sputum,” where pinkish or rust-colored streaks run through otherwise whitish or yellowish phlegm. When actual clots form, they tend to be soft, gelatinous lumps ranging from pea-sized to roughly the size of a grape. Their color offers clues about timing: bright red usually means fresh, active bleeding, while darker red or brownish clots suggest the blood pooled in the airways for a while before being coughed out.
Texture varies too. A fresh clot feels slippery and jelly-like, somewhat similar to the consistency of liver. Older clots that have partially dried or mixed heavily with mucus can feel more rubbery or fibrous. Some people describe the material as looking like coffee grounds when the blood has been partially digested by stomach acid, but that scenario usually points toward a gastrointestinal bleed rather than a lung source.
Bronchial Casts and Tree-Shaped Clots
The most visually striking form of a coughed-up clot is the bronchial cast, a branching structure that mirrors the shape of the airways it formed inside. These can look almost like a small, reddish tree or a coral branch. They hold their shape after being expelled because the material, usually a mix of fibrin, blood cells, and mucus, solidified while sitting in the bronchial tubes. A well-known historical report described a 22-year-old woman who coughed up a cast measuring 10 centimeters long, with branches extending down to very small airways deep in the lung.
Bronchial casts arise in a condition called plastic bronchitis, a rare disorder where thick, cohesive material accumulates and literally molds itself to the airways. In children, plastic bronchitis often follows certain heart surgeries or accompanies severe respiratory infections. In adults, cases have been linked to underlying lung disease, though some patients have no clear pulmonary condition at all. There are two recognized cast types: one associated with inflammatory diseases and another linked to surgical procedures.
How Coughed-Up Blood Differs from Vomited Blood
People often struggle to tell whether blood came from the lungs or the stomach, and the distinction matters because the causes and treatments differ sharply. Blood from the lungs, known as hemoptysis, tends to be bright red or pink, frothy (because it mixes with air in the airways), and accompanied by the urge to cough. Blood from the stomach, called hematemesis, is usually darker, sometimes resembling coffee grounds, and comes up with retching or vomiting rather than coughing. Stomach blood often has food particles mixed in and may carry an acidic taste.
That said, the overlap between the two can be surprisingly messy in real life. A large bleed in the lungs can trickle into the throat and be swallowed, only to be vomited back up later, making it look like a GI bleed. Conversely, someone vomiting blood forcefully may aspirate a small amount and then cough it back up, mimicking hemoptysis. When there is any ambiguity, doctors rely on imaging and endoscopy rather than appearance alone.
Common Causes of Coughing Up Blood Clots
The list of things that can make you cough up blood is long, but a handful of causes account for the majority of cases. Infections sit near the top. Bronchitis, pneumonia, and tuberculosis can all erode small blood vessels in the airways or lung tissue, producing bloody sputum that sometimes clots. Chronic conditions like bronchiectasis, where the airways are permanently widened and damaged, make people especially prone to repeated episodes.
Lung cancer is another well-known cause, though it accounts for a smaller share of hemoptysis cases than most people assume. Still, coughing up blood can be one of the first noticeable symptoms of a lung tumor, particularly in current or former smokers. One study of patients with symptoms suggestive of lung cancer found that people who had never before coughed up blood recognized it as unusual enough to seek medical evaluation, even though they initially hoped the symptom would resolve on its own.
Pulmonary embolism, where a blood clot lodges in the lung’s blood vessels, can also trigger hemoptysis. The bleeding in these cases comes from tissue that has been deprived of blood flow and begins to break down. Anticoagulant medications prescribed for other conditions can contribute too, by making it harder for small bleeds to seal themselves off.
Autoimmune and Systemic Conditions
Sometimes coughing up blood signals a problem far beyond the lungs themselves. Diffuse alveolar hemorrhage is a condition where bleeding occurs across large areas of the tiny air sacs deep in the lungs. The blood seeps into spaces where oxygen exchange normally takes place, and what comes up when the person coughs can range from pink, frothy fluid to frank blood clots. The material often looks uniformly bloody rather than showing the streaky, mucus-mixed pattern typical of bronchial infections.
Most cases of diffuse alveolar hemorrhage stem from inflammation of the smallest blood vessels, a process driven by autoimmune diseases. Conditions like ANCA-associated vasculitis, anti-glomerular basement membrane disease, and lupus are among the most common culprits. In vasculitis specifically, the inflammation damages capillary walls in the lungs, causing structural breakdown and hemorrhage into the air sacs. The condition can also result from clotting disorders, certain medications, inhaled toxins, or organ transplantation.
When Blood Volume Becomes Dangerous
Most hemoptysis episodes involve small amounts of blood, teaspoons rather than cupfuls, and resolve without emergency intervention. But the line between inconvenient and life-threatening can blur quickly. Clinicians use the term “massive hemoptysis” for episodes that create an immediate threat to survival, though the definition is not strictly tied to a specific volume. What qualifies as massive is any amount of bleeding that impairs a person’s ability to breathe, destabilizes blood pressure, or threatens respiratory failure.
This matters because even a relatively modest volume of blood in the airways can be lethal if it floods the side of the lung that is still working. The danger is less about blood loss and more about drowning. A person coughing up large, formed clots in rapid succession, or producing bright red blood continuously for more than a few minutes, needs emergency care. Lying on the side of the suspected bleeding lung, if known, can help keep blood from spilling into the healthy lung while awaiting treatment.
How Doctors Track Down the Source
Figuring out exactly where the blood is coming from inside the lungs is not always straightforward. Doctors use a combination of imaging and direct visualization. A standard chest X-ray is the usual first step but only identifies the bleeding site in about a third of cases. High-resolution CT scans and bronchoscopy, where a flexible camera is passed into the airways, both perform considerably better. In one study of intensive-care patients with hemoptysis, bronchoscopy identified the bleeding site in roughly nine out of ten cases, and CT scanning performed similarly. When either test alone failed, using both together located the source in nearly all patients.
Bronchoscopy has the added advantage of being both diagnostic and, in some situations, therapeutic. A doctor can suction out clots, apply medications to constrict bleeding vessels, or place a balloon to tamponade a bleeding airway, all during the same procedure. For bleeding that cannot be controlled through the bronchoscope, bronchial artery embolization is a common next step. In this procedure, an interventional radiologist threads a catheter through the blood vessels to the artery feeding the bleed and blocks it off with tiny particles or coils.
Fibrin Casts from Toxic Inhalation
An unusual type of airway cast forms not from chronic disease but from acute exposure to inhaled toxins. Sulfur mustard, a chemical warfare agent, causes severe lung injury that triggers the formation of fibrin casts capable of blocking airways at multiple levels. The mechanism involves a rapid activation of the clotting cascade inside the airways themselves. Damaged airway cells release a substance called tissue factor, which kick-starts clot formation directly in the bronchial tubes. The resulting casts are dense, fibrin-rich plugs that obstruct breathing and can cause respiratory failure.
While sulfur mustard exposure is thankfully rare outside military and industrial settings, this type of cast formation has been studied extensively because it reveals how the lungs’ own clotting response can become a threat. The casts differ from those seen in plastic bronchitis: they are composed primarily of fibrin rather than a mix of mucus, inflammatory cells, and cellular debris. They tend to form rapidly, within hours of exposure, and can obstruct enough of the airway to be fatal without prompt removal.
What Children Cough Up Versus Adults
Hemoptysis in children is far less common than in adults and usually has different causes. Infections, particularly lower respiratory tract infections and cystic fibrosis exacerbations, are the most frequent triggers. Foreign body aspiration, where a child inhales a small object that damages the airway lining, is another possibility that rarely applies to adults.
The plastic bronchitis picture also looks different in children. Pediatric cases often arise after Fontan procedures, a type of heart surgery performed for certain congenital heart defects. In these children, altered blood flow and lymphatic drainage appear to promote the formation of thick, rubbery casts in the airways. The casts can be dramatic in size relative to the child’s small airways, and the symptoms, which include coughing, wheezing, and respiratory distress, may recur over months or years. Type II casts, linked to surgical causes, are the form most often seen in this population.
Practical Questions Most People Have
If you cough up something bloody and are trying to decide how worried to be, a few practical details are worth noting. A single episode of blood-streaked mucus during a bad cold or bronchitis flare is common and usually not an emergency, though mentioning it to your doctor at your next visit is sensible. Repeated episodes, clots larger than a small coin, or blood that appears without any obvious respiratory infection deserve same-day medical attention.
Saving what you coughed up, as unpleasant as that sounds, can help your doctor enormously. Place it in a clear bag or container. The color, consistency, and volume all provide diagnostic clues. Snap a photo on your phone if collecting the material itself is not feasible. Note whether the blood came up with a cough, with vomiting, or seemed to appear in your mouth without either, because each pattern points in a different diagnostic direction.
People on blood thinners should be especially attentive. These medications do not cause hemoptysis on their own, but they make it harder for any small bleed to stop, turning what might have been a minor streak into a more persistent problem. If you are taking anticoagulants and notice blood in your sputum, contact your prescribing doctor promptly rather than waiting to see if it resolves.
Why Appearance Alone Does Not Tell You the Cause
It is tempting to try to diagnose yourself based on what the blood looks like, and to some extent the visual clues do help narrow things down. Bright red, frothy blood usually means active bleeding from the airways. Dark, clotted material mixed with mucus suggests a slower or intermittent bleed. A branching, cast-like structure points toward plastic bronchitis or a related process. Uniformly pink or blood-tinged fluid coming up in large volumes raises concern for diffuse alveolar hemorrhage.
But these visual patterns overlap enough that no one, including experienced physicians, relies on appearance alone to make a diagnosis. The same bright red blood could come from a ruptured bronchial artery, an eroded tumor, or an area of lung tissue damaged by a clot in the pulmonary circulation. The same dark, clotted material could reflect old blood from a resolving pneumonia or a slow-growing cancer. Imaging, lab work, and sometimes bronchoscopy are what ultimately distinguish one cause from another. What you can do at home is note the details carefully and get them to a doctor who can put the visual puzzle together with the rest of the clinical picture.
Clots That Come Back
Recurrent hemoptysis, where someone coughs up blood or clots repeatedly over weeks or months, has its own set of implications. In many cases, the underlying cause is a chronic structural problem: bronchiectasis, a vascular malformation in the lung, or a condition that keeps irritating the airway lining. These patients often learn to distinguish their “usual” episodes from something new, though any change in volume, color, or frequency warrants re-evaluation.
For patients with recurrent massive or near-massive episodes, bronchial artery embolization can provide lasting relief. In one reported case involving a patient with pulmonary embolism and severe hemoptysis, embolization successfully stopped the hemorrhage and allowed anticoagulant therapy to be started safely a few days later.1PubMed Central. Massive hemoptysis in a patient with pulmonary embolism, a real therapeutic conundrum The procedure works by cutting off blood supply to the vessels that are feeding the bleed. It is not always permanent, since new blood vessels can grow to replace the blocked ones, but it buys time and can be repeated if needed.
People who experience repeated episodes of coughing up clots without an identified cause sometimes undergo CT angiography, which maps the blood vessels in the chest in fine detail. A surprising number of cases that initially seem mysterious turn out to involve abnormal bronchial arteries that have enlarged over time, feeding chronic low-grade bleeding that only becomes visible when it clots and is coughed up.