Tumor lysis syndrome (TLS) is a potentially life-threatening condition that happens when a large number of cancer cells die rapidly and release their contents into the bloodstream. This flood of cellular debris overwhelms the body’s ability to process it, causing dangerous shifts in blood chemistry that can damage the kidneys, disrupt heart rhythm, and trigger seizures. It most commonly occurs within 12 to 72 hours after starting cancer treatment, though it can occasionally happen on its own in fast-growing cancers.
How Cancer Cell Death Causes a Chain Reaction
Every cell in your body contains potassium, phosphorus, and the building blocks of DNA called purines. Normally, when cells die, the body recycles or excretes these substances at a manageable pace. In TLS, millions of cancer cells break apart at once, dumping massive quantities of these materials into the blood faster than the kidneys can clear them.
Three things happen almost simultaneously. First, potassium levels spike. High potassium is dangerous because it interferes with the electrical signals that keep your heart beating in rhythm. Second, phosphorus floods the bloodstream. Excess phosphorus binds to calcium, pulling calcium out of circulation and depositing calcium-phosphate crystals in soft tissues. The resulting drop in calcium can cause muscle cramps, spasms, and seizures. Third, the purines released from broken-down DNA get converted into uric acid by the liver. At very high concentrations, uric acid forms crystals inside the tiny tubes of the kidneys, physically blocking them. This raises pressure inside the kidneys, reduces blood flow, and can lead to acute kidney failure.
Symptoms to Recognize
TLS doesn’t always announce itself with dramatic symptoms early on. The first signs are often picked up through blood tests rather than how a person feels. When symptoms do appear, they reflect the specific electrolyte imbalances happening underneath.
High potassium can cause nausea, muscle weakness, a slow or irregular heartbeat, and in severe cases, cardiac arrest. Low calcium often shows up as tingling around the mouth or in the fingers, muscle twitching, cramps, or confusion. As uric acid builds up and kidney function declines, you may notice decreased urine output, swelling, fatigue, and a general feeling of being unwell. Some people experience vomiting, diarrhea, or abdominal discomfort. In the most serious cases, seizures or dangerous heart rhythm changes can occur without much warning, which is why patients at risk are monitored closely with frequent lab draws.
Which Cancers Carry the Highest Risk
TLS is most common in blood cancers, particularly those that grow quickly or respond dramatically to treatment. The highest-risk cancers include acute lymphoblastic leukemia (ALL), Burkitt’s lymphoma, and advanced-stage lymphoblastic lymphoma. Acute myeloid leukemia with a high white blood cell count (above 25,000 per microliter) also falls into the high-risk category, as does chronic lymphocytic leukemia treated with certain targeted therapies when the disease burden is large.
Intermediate-risk situations include other forms of aggressive lymphoma when the tumor burden is moderate, as well as certain solid tumors like small cell lung cancer, germ-cell tumors, and neuroblastoma. Most solid tumors, multiple myeloma, and slower-growing lymphomas carry a lower risk, though it’s not zero.
Several factors push someone into a higher risk category regardless of cancer type: existing kidney problems, elevated uric acid before treatment begins, a very high white blood cell count, bulky disease (any tumor mass 7.5 cm or larger), and elevated lactate dehydrogenase (LDH), a blood marker that reflects how fast cells are turning over. Kidney dysfunction is especially important because the kidneys are the primary exit route for the substances that cause TLS. If they’re already compromised, even a moderate amount of cell death can overwhelm them.
How It’s Diagnosed
Doctors use a standardized system called the Cairo-Bishop criteria to classify TLS. Laboratory TLS is diagnosed when blood tests show two or more of the following within a short window around the start of treatment:
- Uric acid at or above 8 mg/dL, or a 25% increase from baseline
- Potassium at or above 6.0 mEq/L, or a 25% increase from baseline
- Phosphorus above normal thresholds, or a 25% increase from baseline
- Calcium below 7.0 mg/dL, or a 25% decrease from baseline
Laboratory TLS means the blood chemistry is deranged but hasn’t yet caused organ damage. Clinical TLS is more serious. It’s diagnosed when laboratory TLS is present along with at least one clinical complication: kidney injury, seizures, cardiac arrhythmia, or death. The distinction matters because clinical TLS requires more aggressive intervention and carries a significantly worse prognosis.
Prevention: Hydration and Medication
The most effective strategy for TLS is preventing it before it starts. Aggressive intravenous hydration is the cornerstone. The goal is to keep the kidneys flushing out uric acid, potassium, and phosphorus as fast as they’re being released. Guidelines recommend fluid intake high enough to maintain urine output of 80 to 100 mL per square meter of body surface area per hour. In practical terms, this means patients receive a high volume of IV fluids starting before chemotherapy and continuing for at least 24 to 48 hours afterward. One important note: urine alkalinization with sodium bicarbonate, once a common practice, is no longer recommended because raising urine pH can actually promote calcium-phosphate crystal formation.
Two medications are used to control uric acid, and they work in fundamentally different ways. Allopurinol blocks the liver enzyme that converts purines into uric acid in the first place. It’s effective, but it takes 24 to 72 hours to work and only prevents new uric acid from forming. It does nothing to lower uric acid that’s already circulating. For this reason, it’s ideally started one to two days before chemotherapy begins. Allopurinol is the standard choice for patients at low to intermediate risk.
For high-risk patients, or those who already have elevated uric acid, rasburicase is the more powerful option. Rather than blocking uric acid production, rasburicase is an enzyme that directly breaks down existing uric acid into a much more soluble substance called allantoin, which the kidneys can easily clear. It works within hours, making it especially valuable when treatment can’t be delayed or when uric acid is already dangerously high.
Who Cannot Receive Rasburicase
Rasburicase is contraindicated in people with G6PD deficiency, a genetic condition that affects roughly 400 million people worldwide, particularly those of African, Mediterranean, and Southeast Asian descent. The reason is specific: rasburicase produces hydrogen peroxide as a byproduct when it breaks down uric acid. Normally, red blood cells neutralize hydrogen peroxide using a protective molecule called NADPH. But in G6PD deficiency, red blood cells can’t produce enough NADPH. The hydrogen peroxide generated by rasburicase overwhelms their defenses, causing the red blood cells themselves to rupture. This can trigger severe hemolytic anemia and a condition called methemoglobinemia, where the blood can’t carry oxygen efficiently. Screening for G6PD deficiency is recommended before administering rasburicase.
How Kidney Damage Develops
Acute kidney injury is the most common serious complication of TLS and the one that drives much of the urgency around prevention. The mechanism is largely mechanical. As the kidneys filter enormous quantities of uric acid from the blood, the fluid inside the kidney’s tubules becomes progressively more concentrated and more acidic. Uric acid is far less soluble in acidic environments, so crystals form directly inside the tubules and collecting ducts. These crystals physically obstruct the flow of urine, raising pressure within the kidney. That increased pressure compresses the small veins surrounding the kidney tubules, reducing blood flow. The combination of blocked tubules and reduced blood flow causes a rapid decline in the kidney’s filtering capacity.
Calcium-phosphate crystals can cause additional damage through a similar process. When phosphorus and calcium levels are both elevated, these crystals precipitate in kidney tissue and other organs, compounding the obstruction. If kidney function deteriorates severely and doesn’t respond to fluids and medication, dialysis becomes necessary to mechanically filter the blood until the kidneys recover.
What Monitoring Looks Like
Patients identified as being at risk for TLS undergo frequent blood draws, sometimes every 4 to 6 hours during the first 24 to 72 hours of treatment. These labs check potassium, phosphorus, calcium, uric acid, and kidney function markers. Urine output is tracked closely, and cardiac monitoring is often in place for high-risk patients because dangerous heart rhythms from high potassium can develop quickly.
Patients at risk are also kept off routine electrolyte replacement protocols. Adding potassium or calcium supplements, which are standard in many hospital settings, could worsen the very imbalances TLS creates. Managing TLS is a balancing act: the medical team needs to treat the cancer aggressively enough to be effective while keeping the metabolic fallout from that treatment under control.