What does the Immuknow (Immune Know) whole blood test measure?

ImmuKnow Whole Blood Test: Measuring CD4 T-Cell Immune Function

The ImmuKnow whole blood test measures the level of intracellular adenosine triphosphate (ATP) in CD4+ T lymphocytes after stimulation with phytohemagglutinin, providing a global assessment of cellular immune function. 1

Purpose and Clinical Applications

• The ImmuKnow assay is FDA-approved for monitoring the immune status of immunosuppressed patients, particularly transplant recipients, to help balance immunosuppression levels 1
• The test helps identify patients at risk for infection due to over-immunosuppression or at risk for rejection due to under-immunosuppression by measuring CD4 T-cell activation 2
• It serves as a functional immune assay that complements other laboratory tests used in immune function assessment, such as flow cytometry to enumerate CD4 and CD8 T cells 3

Technical Aspects

• The test uses the plant lectin phytohemagglutinin to stimulate lymphocytes in a whole blood sample 1
• After stimulation, an ATP assay measures the degree of activation specifically in CD4+ T cells 1
• Results are reported in ng/mL of ATP, reflecting the metabolic activity and functional capacity of CD4+ T cells 4
• The test falls under the category of "advanced tests" for cellular immunity as outlined in immunodeficiency evaluation guidelines 3

Reference Ranges and Interpretation

• For adults, ImmuKnow assay zones (in ng/mL ATP) are classified as:

  • Strong immune function: >525 ng/mL
  • Moderate immune function: 225-525 ng/mL
  • Low immune function: <225 ng/mL 1

• For children under 12 years, the corresponding zones are:

  • Strong immune function: >395 ng/mL
  • Moderate immune function: 175-395 ng/mL
  • Low immune function: <175 ng/mL 1

• In transplant recipients, significantly lower values are typically observed compared to healthy individuals 1, 4

Clinical Utility in Transplantation

• In kidney transplant patients, low ImmuKnow values (<238 ng/mL) have been associated with infection risk with high sensitivity and specificity 5
• High values (>497 ng/mL) may indicate increased risk of rejection in some transplant populations 5
• The test has shown correlation with clinical status in pediatric liver transplant recipients, serving as a parameter of cellular immune function 4
• In hematopoietic stem cell transplantation, the assay has demonstrated potential for early detection of complications like infection and GVHD 6

Advantages Over Other Immune Monitoring Methods

• Provides functional assessment of immune cells rather than just quantitative measurement 1, 4
• Less variable than absolute CD4 counts which require multiple measurements (WBC count, lymphocyte differential, and percentage of lymphocytes that are CD4+ T-cells) 7
• Offers a rapid, global assessment of immune function that can be used alongside traditional monitoring methods 6

Limitations and Considerations

• Some studies have found limited correlation between ImmuKnow results and rejection episodes in kidney transplantation 2
• Results should be interpreted in the context of clinical presentation and other laboratory findings 4
• The test measures only one aspect of immune function (CD4+ T cell activity) and may not reflect the complete immune status 3
• Reference ranges may vary between different patient populations and clinical contexts 1, 5

Clinical Implementation

• The test is typically used as part of a comprehensive immune monitoring approach rather than as a standalone test 3
• Serial measurements over time may be more informative than single readings 4, 6
• Results should be considered alongside drug levels, clinical status, and other immune parameters 4