Improving the timeframe between blood collection and interferon gamma release assay using T-Cell Xtend®

Area of Science:

• Immunology
• Clinical Diagnostics
• Biotechnology

Background:

• The TSPOT.TB assay requires timely processing of blood samples, typically within 8 hours using Vacutainer CPT tubes.
• Extended blood storage times can impact lymphocyte counts and assay performance, leading to potential delays and indeterminate results.
• There is a need for methods to preserve blood sample integrity for delayed processing in immunological assays.

Purpose of the Study:

• To evaluate the efficacy of T-Cell Xtend in preserving lymphocyte number and function in stored blood samples.
• To assess the performance of the TSPOT.TB assay using blood samples treated with T-Cell Xtend after extended storage.
• To determine if T-Cell Xtend can enable delayed processing of blood samples for TSPOT.TB testing.

Main Methods:

• Whole blood was collected in Vacutainer CPT tubes and lithium heparin (LH) tubes.
• T-Cell Xtend was added to LH tubes after 24 or 48 hours of storage; untreated LH tubes served as controls.
• Peripheral Blood Mononuclear Cells (PBMCs) were isolated, and cell counts (WBC, lymphocytes, granulocytes) were determined. TSPOT.TB assay performance was evaluated.

Main Results:

• T-Cell Xtend treatment maintained lymphocyte proportions in PBMCs comparable to fresh samples, unlike untreated LH samples which showed significant decreases.
• T-Cell Xtend effectively reduced granulocyte proportions in PBMC isolates, restoring them to levels similar to those from CPT tubes.
• The TSPOT.TB assay demonstrated good agreement between CPT-processed samples and T-Cell Xtend treated LH samples, even after 48 hours of storage.

Conclusions:

• T-Cell Xtend effectively removes granulocytes and preserves lymphocyte proportions in blood samples, facilitating delayed processing.
• TSPOT.TB test results from T-Cell Xtend treated samples are comparable to those from the standard CPT method.
• Using standard lithium heparin tubes with T-Cell Xtend allows for up to 48-hour blood sample storage for batched processing, potentially reducing indeterminate TSPOT.TB results.