Test Id : SILRP
Interleukin 2 Receptor Alpha Soluble, Plasma
Useful For
Suggests clinical disorders or settings where the test may be helpful
Measuring the concentration of soluble interleukin 2 receptor alpha (sIL-2Ra) in plasma
Aids in the diagnosis, evaluation and monitoring of patients with hemophagocytic lymphohistiocytosis, macrophage activation syndrome, sarcoidosis, and lymphoid malignancies
Highlights
This test aids the diagnosis and evaluation of lymphoproliferative disorders and hyperinflammatory syndromes such as hemophagocytic lymphohistiocytosis, and macrophage activation syndrome.
Method Name
A short description of the method used to perform the test
Immunoassay
NY State Available
Indicates the status of NY State approval and if the test is orderable for NY State clients.
Reporting Name
Lists a shorter or abbreviated version of the Published Name for a test
Aliases
Lists additional common names for a test, as an aid in searching
CD25
Cytokine
cytokines
IL 2 Receptor
IL-2R
IL2R
IL2RS
Interleukin 2 Receptor
sCD25
Soluble CD25/IL-2 R
Soluble IL-2 Receptor alpha
Soluble Interleukin-2 Receptor Alpha
Specimen Type
Describes the specimen type validated for testing
Plasma EDTA
Ordering Guidance
If this test is ordered with TH1CP / T-Helper Cell Type 1 Cytokine Panel, Plasma or CYTOP / Cytokine Panel, Plasma, this test will be canceled as duplicate and TH1CP or CYTOP performed as ordered.
Specimen Required
Defines the optimal specimen required to perform the test and the preferred volume to complete testing
Supplies: Sarstedt Aliquot Tube, 5 mL (T914)
Collection Container/Tube: Lavender top (EDTA)
Submission Container/Tube: Plastic vial
Specimen Volume: 0.5 mL Plasma
Collection Instructions:
1. Immediately after specimen collection, place the tube on wet ice.
2. Within 2 hours of collection, centrifuge at 4 degrees C, 1500 x g for 10 minutes, and aliquot plasma into a plastic vial.
3. Freeze immediately.
Additional Information:
1. Plasma for this test cannot be shared with other tests. Submit specimen for this test in its own vial.
2. This test cannot be added onto a previously collected specimen.
3. If a refrigerated centrifuge is not available, it is acceptable to use a room temperature centrifuge, provided the sample is kept on ice before centrifugation and is frozen immediately afterward.
Specimen Minimum Volume
Defines the amount of sample necessary to provide a clinically relevant result as determined by the testing laboratory. The minimum volume is sufficient for one attempt at testing.
Plasma: 0.3 mL
Reject Due To
Identifies specimen types and conditions that may cause the specimen to be rejected
| Gross hemolysis | Reject |
| Gross lipemia | Reject |
| Gross icterus | Reject |
| Heat-treated specimen | Reject |
Specimen Stability Information
Provides a description of the temperatures required to transport a specimen to the performing laboratory, alternate acceptable temperatures are also included
| Specimen Type | Temperature | Time | Special Container |
|---|---|---|---|
| Plasma EDTA | Frozen | 14 days |
Useful For
Suggests clinical disorders or settings where the test may be helpful
Measuring the concentration of soluble interleukin 2 receptor alpha (sIL-2Ra) in plasma
Aids in the diagnosis, evaluation and monitoring of patients with hemophagocytic lymphohistiocytosis, macrophage activation syndrome, sarcoidosis, and lymphoid malignancies
Clinical Information
Discusses physiology, pathophysiology, and general clinical aspects, as they relate to a laboratory test
The interleukin 2 receptor alpha chain (IL-2Ra, CD25) is a cell-surface transmembrane protein known to be upregulated on activated T cells. During lymphocyte activation, the extracellular domain is cleaved via extracellular proteolysis to generate a soluble form, soluble IL-2 receptor alpha (sIL-2Ra, sCD25), which circulates in plasma, serving as a marker of T cell and broader lymphocyte activation.
The primary application of sIL-2Ra is the evaluation and monitoring of hemophagocytic lymphohistiocytosis (HLH) and macrophage activation syndrome (MAS) in both adult and pediatric patients.(1,2) According to the HLH-2004 diagnostic and therapeutic guidelines(2), an elevated sIL-2Ra concentration is one of eight diagnostic criteria used in the evaluation of HLH and reflects the marked T cell activation observed in hyperinflammatory disorders such as HLH and MAS. The HLH-2004 diagnostic and therapeutic guidelines established a threshold of greater than 2400 U/mL, derived largely in a pediatric context.(2) A later study in adults reported a comparable optimal threshold of 2515 U/mL.(1) It is important to note, however, that sIL-2Ra measurements are not harmonized across laboratories, and these thresholds do not generalize across assays.(3) Consequently, it has been suggested that a value of approximately 4 times the laboratory-specific upper reference limit may offer a more comparable interim approach across laboratories, pending large multicenter validation studies.(4)
Beyond hyperinflammatory disorders, sIL-2Ra is a clinically established marker in other T cell driven and granulomatous conditions such as sarcoidosis(5) and lymphoproliferative disorders, including T-cell leukemia/lymphoma where sIL-2Ra serves as a marker of tumor burden and prognosis.(6)
Reference Values
Describes reference intervals and additional information for interpretation of test results. May include intervals based on age and sex when appropriate. Intervals are Mayo-derived, unless otherwise designated. If an interpretive report is provided, the reference value field will state this.
<18 years: Not established
> or =18 years: < or =1929 pg/mL
Interpretation
Provides information to assist in interpretation of the test results
Elevated concentrations of soluble interleukin 2 receptor alpha (sIL-2Ra) of approximately 4 times the upper reference limit are one of the diagnostic criteria for hemophagocytic lymphohistiocytosis (HLH) syndrome. The diagnosis of HLH syndrome should be based on compatible clinical presentation in the context of significantly elevated inflammatory markers, including ferritin, sIL-2Ra, and interferon gamma effectors such as CXCL9 (C-X-C motif chemokine ligand 9).
Cautions
Discusses conditions that may cause diagnostic confusion, including improper specimen collection and handling, inappropriate test selection, and interfering substances
Soluble interleukin 2 receptor alpha (sIL-2Ra) testing should only be used in conjunction with clinical presentation and other laboratory testing as part of a patient's overall assessment. Elevations in sIL-2Ra can be seen in several inflammatory, malignancy, or infectious conditions involving activation of T cells, B cells, granulocytes or natural killer cells. Non-elevated concentration of sIL-2Ra does not exclude the possibility of infection or other inflammatory condition.
There is substantial overlap in elevated sIL-2Ra in patients with other chronic inflammatory conditions or infections.
Soluble interleukin 2 receptor alpha is a marker for lymphocyte activation and proliferation; a comprehensive cytokine evaluation such as CYTOP / Cytokine Panel, Plasma may be more useful in overall disease assessment or pathophysiology.
Clinical Reference
Recommendations for in-depth reading of a clinical nature
1. Hayden A, Lin M, Park S, et al. Soluble interleukin-2 receptor is a sensitive diagnostic test in adult HLH. Blood Advances. 2017;1(26):2529-2534. doi:10.1182/bloodadvances.2017012310
2. Henter JI, Horne A, Arico M, et al. HLH-2004: Diagnostic and therapeutic guidelines for hemophagocytic lymphohistiocytosis. Pediatr Blood Cancer. Feb 2007;48(2):124-31. doi:10.1002/pbc.21039
3. Damoiseaux J. The IL-2 – IL-2 receptor pathway in health and disease: The role of the soluble IL-2 receptor. Clin Immunol. 2020;218:108515. doi.10.1016/j.clim.2020.108515
4. Fauser J, Klotz W, Trebo M, et al. The diagnostic pitfall of sIL-2R in hemophagocytic lymphohistiocytosis: A key marker lost in analytic translation. Journal of Allergy and Clinical Immunology. 2026;157(1):275-276. doi:10.1016/j.jaci.2025.09.005
5. Eurelings LEM, Miedema JR, Dalm V, et al. Sensitivity and specificity of serum soluble interleukin-2 receptor for diagnosing sarcoidosis in a population of patients suspected of sarcoidosis. PLoS One. 2019;14(10):e0223897. doi:10.1371/journal.pone.0223897
6. Shiratori S, Kosugi-Kanaya M, Shigematsu A, et al. Ultra-high level of serum soluble interleukin-2 receptor at diagnosis predicts poor outcome for angioimmunoblastic T-cell lymphoma. Leuk Lymphoma. 2015;56(9):2592-2597. doi:10.3109/10428194.2014.1001985
7. Kobayashi Y, Sato T, Nagai T, et al. Association of high serum soluble interleukin 2 receptor levels with risk of adverse events in cardiac sarcoidosis. ESC Heart Fail. 2021;8(6):5282-5292
8. Zoref-Lorenz A, Murakami J, Hofstetter L, et al. An improved index for diagnosis and mortality prediction in malignancy-associated hemophagocytic lymphohistiocytosis. Blood. 2022;139(7):1098-1110
Method Description
Describes how the test is performed and provides a method-specific reference
Testing for soluble interleukin 2 receptor alpha is performed using a laboratory-developed immunoassay.(Unpublished Mayo method)
PDF Report
Indicates whether the report includes an additional document with charts, images or other enriched information
Day(s) Performed
Outlines the days the test is performed. This field reflects the day that the sample must be in the testing laboratory to begin the testing process and includes any specimen preparation and processing time before the test is performed. Some tests are listed as continuously performed, which means that assays are performed multiple times during the day.
Thursday
Report Available
The interval of time (receipt of sample at Mayo Clinic Laboratories to results available) taking into account standard setup days and weekends. The first day is the time that it typically takes for a result to be available. The last day is the time it might take, accounting for any necessary repeated testing.
Specimen Retention Time
Outlines the length of time after testing that a specimen is kept in the laboratory before it is discarded
Performing Laboratory Location
Indicates the location of the laboratory that performs the test
Fees
Several factors determine the fee charged to perform a test. Contact your U.S. or International Regional Manager for information about establishing a fee schedule or to learn more about resources to optimize test selection.
- Authorized users can sign in to Test Prices for detailed fee information.
- Clients without access to Test Prices can contact Customer Service 24 hours a day, seven days a week.
- Prospective clients should contact their account representative. For assistance, contact Customer Service.
Test Classification
Provides information regarding the medical device classification for laboratory test kits and reagents. Tests may be classified as cleared or approved by the US Food and Drug Administration (FDA) and used per manufacturer instructions, or as products that do not undergo full FDA review and approval, and are then labeled as an Analyte Specific Reagent (ASR) product.
This test was developed and its performance characteristics determined by Mayo Clinic in a manner consistent with CLIA requirements. It has not been cleared or approved by the US Food and Drug Administration.
CPT Code Information
Provides guidance in determining the appropriate Current Procedural Terminology (CPT) code(s) information for each test or profile. The listed CPT codes reflect Mayo Clinic Laboratories interpretation of CPT coding requirements. It is the responsibility of each laboratory to determine correct CPT codes to use for billing.
CPT codes are provided by the performing laboratory.
CPT codes are provided by the performing laboratory.
83520
LOINC® Information
Provides guidance in determining the Logical Observation Identifiers Names and Codes (LOINC) values for the order and results codes of this test. LOINC values are provided by the performing laboratory.
| Test Id | Test Order Name | Order LOINC Value |
|---|---|---|
| SILRP | IL-2 Receptor Alpha Soluble, P | 76039-7 |
| Result Id | Test Result Name |
Result LOINC Value
Applies only to results expressed in units of measure originally reported by the performing laboratory. These values do not apply to results that are converted to other units of measure.
|
|---|---|---|
| SILRP | IL-2 Receptor Alpha Soluble, P | 76039-7 |