A pleural effusion, a buildup of fluid in the thin space between the lung and the chest wall, is common in people with cancer, and its color is often the first thing anyone sees. That color is only a hint about the cause. It can raise or lower suspicion, but it can’t confirm or rule out cancer. A few unusual colors say more than the familiar red, because they come from specific substances such as pigment, lymph or bile getting into the fluid. The real answer comes from what the lab finds in the fluid, not from how it looks in the bottle.
Does Bloody Pleural Fluid Mean Cancer
A thoracentesis is the procedure where a needle or thin tube is placed between the ribs to draw the fluid out into bottles or bags. Healthy pleural fluid is a thin, pale yellow layer of only a few spoonfuls, so anything drained is already a large excess.
Among people whose drained fluid looked bloody, cancer was the cause in about 47%.1Chest. Clinical implications of appearance of pleural fluid at thoracentesis A bloody look made cancer only slightly more likely than clear or yellow fluid did.2Chest. Clinical implications of appearance of pleural fluid at thoracentesis
Most cancer-related fluid doesn’t look bloody at all. Only about 11% of cancer-related effusions were bloody,3Chest. Clinical implications of appearance of pleural fluid at thoracentesis so clear or straw-yellow fluid does not rule out cancer. In people already known to have cancer, the check for cancer cells came back positive about as often in bloody fluid as in non-bloody fluid, about 82% in each.4PubMed Central. Does pleural fluid appearance really matter? The relationship between fluid appearance and cytology, cell counts, and chemical laboratory measurements in pleural effusions of patients with cancer
Many other problems turn fluid bloody. Besides cancer, common causes of blood-tinged fluid include a blood clot in the lung, chest injury or surgery, pneumonia, and bleeding problems.5EMCrit Project. Pleural effusion Tuberculosis, kidney failure, asbestos-related inflammation and sometimes heart failure can do the same.6EMCrit Project. Pleural effusion Even a small nick to a blood vessel during the drainage itself can tint the fluid pink. A little blood goes a long way visually, so a red bottle does not mean someone is bleeding heavily inside the chest.
Words matter here. Doctors and labs use different terms for different shades: pink or blood-tinged, frankly bloody, and sometimes “serosanguinous” for straw-colored fluid with a reddish cast. A lab can also measure the fraction of the fluid that is red blood cells (a hematocrit) to tell whether it is truly bloody or just tinted. A red look is a reason to wait for the lab, not to assume the worst.
What Black, Brown and Milky Fluid Can Point To
Black fluid is rare.7PubMed Central. Black Pleural Effusion: A Unique Presentation of Metastatic Melanoma The main causes are fungal infections, melanoma, old bleeding broken down in lung cancer or a leaking pancreatic cyst, and inhaled crack cocaine or charcoal.8PubMed Central. Black Urine and Black Pleural Fluid: A Distinctive Presentation of Metastatic Melanoma In melanoma, the black comes from pigment-filled cancer cells floating in the fluid.9PubMed Central. Black Pleural Effusion: A Unique Presentation of Metastatic Melanoma When lung cancer causes black fluid, it is usually the adenocarcinoma type.10EMCrit Project. Pleural effusion
Brown fluid is also rare. It can come from high levels of bilirubin, the yellow-brown pigment in bile.11PubMed Central. Brown-Colored Malignant Pleural Fluid With High Bilirubin Levels: A Case Series Brown fluid with bilirubin several times higher than in the blood has been seen in people with spread adenocarcinoma from the lung or stomach, without any leak from the bile ducts.12PubMed Central. Brown-Colored Malignant Pleural Fluid With High Bilirubin Levels: A Case Series Old bleeding that has broken down in the chest can also turn fluid dark brown.
Milky fluid is often lymph, the fatty fluid absorbed from digested food, leaking into the chest.13PubMed. Spontaneous recovery of chylothorax caused by lymphoma When it isn’t caused by injury or surgery, the most common cause is cancer, especially lymphoma.14PubMed. Spontaneous recovery of chylothorax caused by lymphoma Swollen lymph nodes can block the main lymph channel in the chest.15PubMed Central. A Case of Chylothorax in Non-Hodgkin Lymphoma
Lymph carries fat, protein and infection-fighting white cells, so repeated drainage of it drains the body of nutrition and immune cells. Over time that can show up as weight loss, weakness and more frequent infections,16PubMed. Spontaneous recovery of chylothorax caused by lymphoma which is why milky fluid is treated promptly.
An unusual color still needs testing, because every color on the list has at least one non-cancer cause. Fungal infection and cocaine use can mimic the black of melanoma, and the bottle looks the same either way. Long-standing fluid of any cause can also turn cloudy and look milky from cholesterol rather than lymph fat.17CAP Today. Crystals Labs measure fats in the fluid to tell true lymph fluid from this look-alike.18CAP Today. Crystals The two have different causes and treatments.
The Test That Actually Shows Cancer
The key test is cytology, where a pathologist, a doctor who specializes in examining cells, looks at the fluid under a microscope for cells that appear cancerous. Sometimes extra stains help identify where a cancer started, such as the lung or breast. A larger sample gives a better chance of finding cells, so the team may send a generous volume.
In people with cancer, the check for cancer cells found them in about 8 in 10 of their effusions, whatever the color.19PubMed Central. Does pleural fluid appearance really matter? The relationship between fluid appearance and cytology, cell counts, and chemical laboratory measurements in pleural effusions of patients with cancer A negative result doesn’t fully rule out cancer, because cells aren’t always shed into the fluid. If suspicion stays high, doctors may repeat the test or take a small sample of the lining. That biopsy shows cancer directly in tissue, and can be done with a camera inserted through a small cut in the chest wall or with a needle guided by imaging. Tissue also allows additional tests on the tumor that help choose treatment.
Tumor markers can add evidence. Doctors may compare the level of CEA, a protein made by some cancers, in the fluid with the level in the blood.20PubMed Central. Ratio of carcinoembryonic antigen in pleural fluid and serum for the diagnosis of malignant pleural effusion When the fluid level was at least as high as the blood level, that pointed to cancer correctly about 9 times in 10.21PubMed Central. Ratio of carcinoembryonic antigen in pleural fluid and serum for the diagnosis of malignant pleural effusion CEA mainly rises with certain cancers such as lung and bowel adenocarcinomas, so it helps alongside the check for cancer cells, not instead of it.
Basic chemistry results, such as protein and LDH, often come back within a day, while the check for cancer cells typically takes several days. The report may say positive, negative or “atypical cells.” Atypical means the cells looked abnormal but not clearly cancerous, so more testing usually follows.
Other Fluid Tests That Help Point to a Cause
Labs compare protein and an enzyme called LDH in the fluid and the blood to sort fluid into two types. Exudate is fluid that leaks out because of inflammation, infection or tumor; transudate is fluid pushed out by pressure, as in heart failure.22Pulmonology Advisor. Diagnosis & Disease Info Cancer-related fluid is almost always the leaky type. These rules aren’t perfect: they wrongly label about 1 in 4 pressure-type effusions as leaky-type, mostly in people taking water pills.23PubMed. The Light criteria: the beginning and why they are useful 40 years later Doctors may run an extra protein comparison when the result is borderline.24PubMed. The Light criteria: the beginning and why they are useful 40 years later
A leaky-type result means a cause such as cancer, infection or inflammation must be looked for. A pressure-type result usually shifts attention to the heart, liver or kidneys.
This is also why doctors test even when cancer is known. Heart strain, pneumonia or clots can cause fluid in people with cancer too, and treatment differs if the fluid isn’t from the cancer.
Other clues turn up in the fluid. Fluid from lymph-channel blockage alone tends to be rich in a type of white cell.25PubMed. Pleural fluid analysis in chylous pleural effusion Unexpected protein or LDH results in milky fluid can signal a second problem that changes treatment.26PubMed. Pleural fluid analysis in chylous pleural effusion
Why Cancer Causes Fluid Around the Lung
Fluid builds up when more is made than the body can remove.27Pulmonology Advisor. Diagnosis & Disease Info When cancer causes the fluid, tumors on the lining make nearby blood vessels leaky, letting fluid seep out.28European Respiratory Review. Malignant pleural effusion: from bench to bedside Cancer in the lymph nodes in the middle of the chest can also block the channels that drain the space.29CancerNetwork. Fluid Complications Tumor cells release signals that inflame the lining and grow new, fragile vessels,30European Respiratory Review. Malignant pleural effusion: from bench to bedside and those vessels can bleed, which helps explain why some cancer-related fluid is bloody.
Fluid with cancer cells in it usually means the cancer has spread to the lining of the chest, which the cancer team factors into the stage and treatment plan. It often returns after draining, so the plan usually includes a way to manage that. Many people get good relief of breathlessness once fluid is drained and managed, even when the underlying cancer is serious.
Breathlessness that builds over days is the most common sign that fluid is collecting again. Chest heaviness or a dry cough can also signal fluid, since it presses on the lung and irritates the lining. After a drain, returning breathlessness should be reported promptly so the team can decide whether to drain again.
How Fluid Around the Lung Is Treated
Draining once often relieves breathlessness quickly. Treating the underlying cancer, such as lymphoma, can make the fluid stop on its own.31PubMed. Spontaneous recovery of chylothorax caused by lymphoma But cancer-related fluid often returns, so longer-term options are used. Pleurodesis, or sealing the space, puts a substance such as talc inside so the lung lining sticks to the chest wall. Alternatively, a soft tube left in place lets people drain fluid at home. For milky lymph fluid that doesn’t settle with diet and drainage, talc sealing can be an option.32PubMed Central. Chemical pleurodesis as a therapeutic option in non-traumatic chylothorax: a scoping review
Sealing the space usually requires a hospital stay of a few days, while a home drain can often be placed as a day procedure. Sealing only works if the lung can re-expand fully against the chest wall after the fluid is drained, so doctors check this first. If the lung cannot re-expand, a home drain is often the better option, since it doesn’t depend on the lung and lining sticking together. Ask the team which suits your lung, your routine and your preferences.
With a home drain, a nurse or trained family member drains the fluid a few times a week, using supplies from the care team. Keep the skin around the tube clean and watch for redness, swelling or discharge. Report fever, a sharp change in the color of the drained fluid, or worsening breathlessness to the care team.