A lysozyme blood test measures the level of lysozyme, a natural antibacterial enzyme, in your blood. Doctors order it most often to help diagnose or monitor sarcoidosis, certain types of leukemia, and granulomatous infections like tuberculosis. The normal range for plasma lysozyme is 2.6 to 6.0 mcg/mL in anyone 12 months or older.
What Lysozyme Does in Your Body
Lysozyme is a small protein that acts as one of your body’s built-in antibiotics. It works by breaking apart the cell walls of bacteria, effectively killing them. You produce it in white blood cells, and it’s also found in tears, saliva, nasal mucus, and breast milk. Alexander Fleming, who later discovered penicillin, first identified lysozyme in 1921.
Because white blood cells (particularly monocytes and macrophages) are the main source of lysozyme in your blood, conditions that cause these cells to multiply or become overactive tend to push blood lysozyme levels higher than normal. That’s what makes the test clinically useful: a rising level can signal that something is driving your immune system into overdrive or that certain white blood cells are growing out of control.
Why Your Doctor Might Order This Test
The lysozyme blood test isn’t a routine screening tool. It’s typically ordered when a doctor already suspects one of a few specific conditions and needs additional evidence to confirm a diagnosis or track disease activity.
The most common reasons include:
- Sarcoidosis: An inflammatory disease that causes clusters of immune cells (granulomas) to form in the lungs, skin, lymph nodes, and other organs. Lysozyme is one of the blood markers used to assess how active the disease is.
- Certain leukemias: Particularly acute myelomonocytic leukemia, chronic myelomonocytic leukemia, and chronic myelocytic leukemia. These cancers involve the same white blood cells that produce lysozyme, so levels rise as those cells proliferate.
- Tuberculosis and other granulomatous infections: Infections that trigger granuloma formation can elevate lysozyme in a pattern similar to sarcoidosis.
- Inflammatory bowel disease: Crohn’s disease, regional enteritis, and ulcerative colitis are all associated with increased lysozyme activity.
- Kidney disease: Severe renal insufficiency, kidney transplant rejection, and various kidney infections can raise levels because the kidneys normally filter lysozyme out of the blood.
How Lysozyme Helps Diagnose Sarcoidosis
Sarcoidosis is one of the primary reasons this test is ordered, and lysozyme has a notably high detection rate for the disease. In studies, serum lysozyme correctly identified sarcoidosis in about 79% of confirmed cases. That’s considerably better than the other common blood marker for sarcoidosis, angiotensin-converting enzyme (ACE), which picked up only about 59% of cases.
What makes lysozyme especially useful is that it catches cases ACE misses. Even when ACE levels came back normal, lysozyme was still elevated in roughly 72% of sarcoidosis patients. The two tests complement each other, so doctors often order both.
Lysozyme levels also track with how widespread the disease is. Levels tend to climb as more organs become involved and differ across the radiographic stages used to classify lung sarcoidosis. Higher peak levels have also been linked to a worse prognosis: patients whose chest X-ray abnormalities persisted for more than five years had significantly higher maximum lysozyme levels than those whose abnormalities resolved. For these reasons, lysozyme is considered particularly good for ongoing monitoring of sarcoidosis once the diagnosis is confirmed, even though it’s less specific than ACE for making the initial diagnosis.
What the Results Mean
The standard reference range, used by Mayo Clinic Laboratories and others, is 2.6 to 6.0 mcg/mL for anyone 12 months and older. Reference values haven’t been established for infants under 12 months.
A result within that range is generally considered normal. A result above 6.0 mcg/mL suggests elevated lysozyme activity, but the number alone doesn’t point to a single cause. To illustrate the range of possibilities: in one study of patients with eye inflammation from various causes, average lysozyme levels in presumed sarcoidosis patients were about 20.7 mg/L, compared to roughly 15.3 mg/L in tuberculosis patients and 12.9 mg/L in healthy controls. The overlap between conditions means your doctor will always interpret the result alongside your symptoms, imaging, and other lab work.
A normal result doesn’t completely rule out disease, either. About 21% of confirmed sarcoidosis cases had normal lysozyme levels in the sensitivity study mentioned above. That’s why the test works best as one piece of a larger diagnostic picture rather than a standalone answer.
How the Test Works
The test itself is a standard blood draw. A technician collects a blood sample from a vein in your arm, and the lab separates out either the serum or plasma to analyze. No specific fasting is typically required for a lysozyme test, though you should follow any instructions your doctor gives you about eating, drinking, or pausing medications beforehand.
In the lab, lysozyme concentration is usually measured by tracking how quickly the enzyme breaks down bacterial cell walls in a controlled sample. The two most common techniques are a turbidimetric assay, which measures how much the cloudiness of a bacterial solution decreases, and a lysoplate assay, which measures clearing zones on a plate coated with bacteria. These methods can produce slightly different absolute numbers, so results from different labs aren’t always directly comparable. Your doctor will interpret your result against the reference range of the specific lab that processed your sample.
Conditions That Can Raise Levels
Because so many conditions can elevate lysozyme, a high result needs context. The full list of associated conditions is broad:
- Granulomatous diseases: sarcoidosis, tuberculosis
- Blood cancers: acute myelomonocytic leukemia, chronic myelomonocytic leukemia, chronic myelocytic leukemia
- Infections: acute bacterial infections, syphilis, urinary tract infections, pyelonephritis
- Inflammatory bowel conditions: Crohn’s disease, ulcerative colitis, regional enteritis
- Kidney problems: severe renal insufficiency, kidney transplant rejection, glomerulonephritis, nephrosis
- Other: megaloblastic anemias (often from vitamin B12 or folate deficiency)
This wide range is exactly why the lysozyme test is rarely used in isolation. It’s most valuable when paired with other tests and clinical findings that narrow down which of these possibilities is actually at play. For sarcoidosis monitoring or leukemia subtyping, it adds a meaningful data point. As a screening tool for a vague set of symptoms, it’s less helpful on its own.