Seeing dark urine can be alarming — especially if you don’t know why it’s happening. “My concern arose after experiencing fatigue during physical activity and seeing dark-colored urine,” one member of myPNHteam shared. Another myPNHteam member said, “For me it was my labs, bone marrow biopsy, and when I told the doctor that my urine was red.”

In some cases, dark urine can be a sign of a rare condition called paroxysmal nocturnal hemoglobinuria (PNH). In PNH, red blood cells break down too much, and the hemoglobin that’s released during this process can be excreted into the urine.

If your pee looks darker than usual, talk to your doctor.

Read on to learn why PNH can cause this symptom and what your urine might look like if you have it.

How Does PNH Cause Dark Urine?

PNH is a blood disease caused by a mutation (change) in the PIGA gene (phosphatidylinositol glycan anchor class A) within a hematopoietic stem cell (a stem cell that is able to generate all kinds of blood cells). Normally, PIGA provides all erythrocytes (red blood cells) with a protein barrier to defend them. This barrier helps protect them against the complement system — blood-based proteins that work with the leukocytes (white blood cells) of the immune system to fight foreign cells like bacteria.

In PNH, red blood cells break down and release hemoglobin into the urine, causing it to look dark or cola-colored.

Instead of creating healthy red blood cells, the PIGA gene mutation causes red blood cells to form without a protein barrier. In people with PNH, the bone marrow — where all types of blood cells are made — replicates the mutated gene, so the mutation is passed to all new stem cells. Because these cells originate from a single abnormal stem cell, they are referred to as PNH clones.

Without their protective barrier, PNH red blood cells are exposed to the attacks of the complement system. These attacks cause red blood cells to break apart sooner than they should. When these cells are destroyed, hemoglobin — the red part of the cell that carries oxygen — can enter your urine (hemoglobinuria), which can change its color, causing it to look dark or cola-colored.

What Does Urine Look Like With PNH?

When the complement system targets PNH red blood cells, it causes them to break apart. During this breaking down process — referred to as hemolysis — a red blood cell’s membrane (external wall) is destroyed. The break in the membrane allows hemoglobin to leak out, eventually appearing in urine.

PNH can affect urine color differently from person to person. If you have PNH, you might notice your pee looks brownish, dark like cola, or — less commonly — red like blood. It may look discolored or it may appear normal.

When Are You Most Likely To Notice Dark Urine With PNH?

Discolored urine that’s dark or cola-colored is the most common symptom of PNH. But when are you more likely to notice urine changes if you have the condition?

Dark urine is often the first sign that someone has PNH. For many people, this symptom is most noticeable at night and first thing in the morning. The name “paroxysmal nocturnal hemoglobinuria” actually refers to hemoglobin that appears in urine during the night.

This happens because although the breakdown of red blood cells happens all the time, urine becomes more concentrated while you sleep. This allows more hemoglobin from the destroyed red blood cells to build up in the bladder, making the color change more noticeable in the morning.

Although dark urine is most noticeable at night and in the early morning, in people with PNH, hemolysis is ongoing. The overnight period — when people are sleeping rather than using the bathroom — simply gives the hemoglobin more time to collect. This means that, if you have PNH, it’s possible for you to have dark urine at any time of day.

You might also notice darker urine more when you’re sick. This is because things that put stress on the body, such as fighting off an infection or recovering from an injury, can act as triggers and make hemolysis worse. In some cases, hemolysis may lower your red blood cell count enough to cause hemolytic anemia. Symptoms of anemia to look out for include pale skin, tiredness, weakness, and dizziness.

Other Reasons For Dark Urine

PNH is a rare blood disorder — it only affects about 6 in 1 million people per year, mostly between the ages of 30 and 40. If you don’t have a PNH diagnosis, keep in mind that there are other reasons that may be more likely causes of your dark urine.

Other possible causes of dark urine include:

• Dehydration
• Eating colorful foods like beets or blueberries
• Liver disease
• Kidney problems, such as kidney disease, kidney stones, or kidney cancer
• Issues with the prostate or bladder, such as enlarged prostate, bladder stones, or cancer
• Certain medications, such as antibiotics
• Urinary tract infections (UTI)
• Mercury or lead poisoning

Your urine color can change for many reasons. If you’re noticing dark urine often and there’s no obvious reason for it, speak with your doctor. They can help you figure out whether the changes to your urine are caused by PNH or something else.

When To Talk to Your Doctor

If you have dark urine frequently, it’s a good idea to talk to your healthcare provider. If your doctor suspects you might have PNH, they may order tests such as flow cytometry — a blood test used to detect PNH cells. It’s especially important to talk with a medical professional if you notice any other symptoms of hemolysis along with your dark urine, such as:

• Fatigue
• Headaches
• Fast heartbeat or chest pains
• Shortness of breath during physical activity

If you have been diagnosed with PNH and are noticing your urine has become darker than usual, reach out to your doctor. Dark urine, especially together with other PNH symptoms, may be a sign that your treatment plan needs to be adjusted.

Other symptoms of PNH that may signal that your condition isn’t well controlled include:

• Severe fatigue or tiredness that affects your quality of life
• Shortness of breath
• Back or abdominal pain
• Problems swallowing or spasms in the esophagus (the tube that carries food from your mouth to your stomach)
• Erectile dysfunction

Always keep your doctor updated on your condition, as PNH can lead to serious complications. Constant hemolysis, for example, can put you at an increased risk of developing thrombosis (blood clots), which can block blood flow to organs. Blood clots, especially in veins, are common with PNH — they happen in 15 percent to 30 percent of people with the condition. If blood clots impact your liver, you’re also at risk of developing Budd-Chiari syndrome, which can cause the liver to swell and collect fluid.

PNH is also associated with other conditions, such as:

• Aplastic anemia
• Myelodysplastic syndrome
• Rarely, transformation to acute leukemia (in less than 3 percent of people)

When in doubt, check in with your hematology provider about any changes in your symptoms. They can help you manage your PNH, improve your quality of life, and reduce your risk of potentially life-threatening complications.

Join the Conversation

On myPNHteam, people share their experiences with paroxysmal nocturnal hemoglobinuria, get advice, and find support from others who understand.

Have you talked with your doctor about dark-colored urine? Let others know in the comments below.