InstalabIL-1
Should you take a IL-1 test?
This test is most useful if any of these apply to you.
About IL-1
IL-1 helps start and amplify inflammation after infection or tissue damage. Its role in inflammatory disease is well established, but measuring it in blood has much less established value. For prevention and longevity screening, this remains an exploratory marker: studies have not established that testing improves decisions or outcomes.
Specialist laboratories offer IL-1 testing as supplementary information in selected inflammatory or infectious conditions. A result cannot establish or exclude a diagnosis, measure your total inflammation, or determine whether you need a particular treatment.
What This Test Measures
IL-1 refers to two related proteins, IL-1α and IL-1β. They belong to a larger family of immune signaling proteins. This test's catalog entry specifies blood and reports results in pg/mL, but it does not identify which form is measured, whether the laboratory uses serum or plasma, or the measurement method. Those details need to be confirmed with the performing laboratory before applying findings from a particular study.
Most of the studies discussed here measured IL-1β in serum or plasma. Serum is the liquid left after blood clots; plasma is separated from blood collected with an agent that prevents clotting. Results from these specimens are not automatically interchangeable. Studies of IL-1α, IL-1 receptor antagonist, or tissue samples provide related biological evidence, but they do not validate an unspecified blood IL-1 measurement.
How the Signal Works
Activated immune cells make IL-1β in response to inflammatory triggers. It starts as an inactive precursor and usually becomes active after an enzyme called caspase-1 cuts it. A group of proteins inside the cell assembles to activate that enzyme. This group is called an inflammasome. Other enzymes can also activate IL-1β.
IL-1α is often already present inside tissue cells and can be released when cells are damaged. Its precursor can be biologically active, so the two forms do not share the same activation requirements. Both can promote fever and inflammation. IL-1 also stimulates IL-6 production, which helps trigger the liver's production of C-reactive protein.
IL-1 receptor antagonist is a separate protein that blocks signaling by IL-1α and IL-1β. It is usually abbreviated IL-1Ra and circulates at higher concentrations than IL-1β. Researchers sometimes measure it to study this pathway, but its concentration is also influenced by other inflammatory signals, body fat, and genetic differences. It is not a direct substitute for an IL-1β result.
Why Blood Levels Can Be Hard to Interpret
Much of IL-1's activity happens within tissues. IL-1β in healthy people's plasma is often near or below the detection limits of commonly used assays. A below-detection result means the laboratory could not reliably detect the protein in that sample; it does not mean the pathway is inactive throughout your body. There is no validated blood target for prevention or longevity.
Rheumatoid Arthritis
An early study found higher plasma IL-1β in people with rheumatoid arthritis than in healthy controls. Levels were associated with joint tenderness, pain, and ESR. ESR is a broad blood marker of inflammation. In a subset with repeated measurements, IL-1β also varied with clinical disease activity. This supports a biological association, but it does not establish a reliable test for diagnosing arthritis or monitoring every flare.
Other studies measured serum IL-1Ra instead. In 407 people with rheumatoid arthritis, disease activity had stronger adjusted associations with IL-1Ra than with IL-6. In another group of 430, IL-1Ra was associated with several cardiovascular risk factors. These findings concern the antagonist protein and cannot be read as findings about your IL-1 concentration.
Rheumatoid arthritis diagnosis depends on symptoms, a joint examination, and supporting tests. Rheumatoid factor and CCP antibodies can support the diagnosis, but negative antibody results do not rule it out. Clinical disease activity and established inflammation markers have a clearer role in routine follow-up than blood IL-1.
Heart and Blood Vessel Disease
Studies in cultured immune cells and mice show that cholesterol crystals can activate inflammatory machinery and promote IL-1β release. Human studies have also linked circulating IL-1β to cardiovascular disease. Those associations do not establish that a blood concentration identifies inflamed plaque or predicts who will have a heart attack.
| Who Was Studied | What Was Measured | What They Found |
|---|---|---|
| 62 participants, including people with angina, people recovering from a heart attack, and healthy controls | Serum IL-1β | Average concentrations were higher in the heart disease groups. The highest average occurred in the group with angina and relatively little artery narrowing. Concentrations did not correlate with the routine inflammation markers studied. |
| 1,292 adults in the InCHIANTI population study | Serum IL-1β | Concentrations were associated with heart failure and angina. The study found no association with age, sex, or use of cardioactive medication; that does not prove these factors can never affect results. |
| Studies of people with early-onset coronary disease | Circulating IL-1 measurements pooled across studies | The review reported higher concentrations in affected groups, but rated the evidence as low quality. It did not validate this catalog test for individual risk assessment. |
These studies compared groups with and without disease. They did not establish that adding an IL-1 test to routine risk assessment improves care, or that an isolated result is a reason to obtain coronary imaging.
What Studies of IL-1Ra Show
Across six population cohorts, higher circulating IL-1Ra was associated with later cardiovascular disease. Adding it to clinical risk models did not produce a statistically significant improvement in risk prediction. In a separate study of 323 people with a heart attack, higher admission plasma IL-1Ra was associated with greater mortality at two and five years after adjustment for other measured risk factors.
Higher IL-1Ra may partly reflect the body's response to inflammation. The observational findings do not show that the antagonist causes those outcomes, and they cannot be transferred to IL-1α or IL-1β concentrations. A high concentration of a pathway blocker and a high concentration of an inflammatory signal have different biological meanings.
Brain Aneurysms and Stroke
An intracranial aneurysm is a weakened, bulging area in a brain artery. A study included 281 people with aneurysms plus comparison groups. Higher serum IL-1β and lower IL-1Ra were associated with ruptured aneurysms in the initial group. A ratio combining the two proteins was then studied in a separate group with unruptured aneurysms, including those causing symptoms. Serum and tissue measurements were correlated in the initial group.
This was research on existing rupture or symptoms, not proof that a blood result predicts future rupture. It does not replace assessment of the aneurysm on imaging. Animal studies also show that IL-1 can worsen injury after stroke, but those findings do not validate blood IL-1 as a stroke warning test.
Severe Infection
Studies of malaria found higher circulating IL-1β in severe disease than in uncomplicated infection, with substantial disagreement between studies. Uncomplicated cases did not differ significantly from healthy comparison groups. Sepsis studies have also reported inconsistent findings, including only slight serum IL-1β increases without a relationship to severity or survival. A low result cannot exclude serious infection.
Why Results Differ Across Diseases
In a study of lupus, serum IL-1β was not associated with disease activity or organ damage. Serum IL-18 was associated with active kidney involvement, but it is a different protein. A study of men with ankylosing spondylitis measured serum IL-1α and IL-1Ra and found no significant difference from controls; it did not establish the behavior of IL-1β.
A review of older adults with age-related diseases found higher IL-6 in affected groups, while its limited IL-1β evidence did not show the same pattern. That comparison does not establish either cytokine as a general screening test. Blood concentrations reflect only part of an inflammatory process, and results depend on the disease, specimen, and assay.
When Results Can Be Misleading
- Very low concentrations: Results near an assay's detection limit are less precise. A small change, including a shift from undetectable to detectable, may reflect measurement variation.
- Different specimens or assays: Serum and plasma can give different results, and laboratories differ in what they detect and how they calibrate the measurement. Using one laboratory helps only if the specimen and assay also remain the same.
- Sample handling: Delayed separation of blood cells can change measured IL-1β. Collection tubes, processing, storage, and transport must follow the performing laboratory's instructions.
- Antibody interference: If an antibody-based assay is used, rheumatoid factor or other interfering antibodies can distort cytokine measurements. The laboratory can investigate a result that conflicts with the clinical picture.
- Illness and treatment: Infection, injury, and inflammatory disease can change the biology being measured. Medicines that alter immune activity can also affect interpretation. These changes do not identify a specific cause.
- IL-1 blocking drugs: Canakinumab can increase measured total IL-1β because some assays detect protein bound to the drug. That bound protein is inactive, so a higher measured result need not mean worsening inflammation.
- Dialysis: An older plasma study found changes in circulating IL-1 during hemodialysis. The finding depends on the clinical setting and does not establish a predictable effect for every current assay.
What Repeated Measurements Can Show
Repeated measurements have been useful in some research settings, including the early rheumatoid arthritis study. There is no established amount of change that reliably means improvement or deterioration across conditions. A personal baseline does not become a validated health target, and repeated testing has not been shown to improve preventive care in healthy people.