What are acceptable specimen matrices for troponin testing?
A: Serum and/or plasma are appropriate for contemporary and high-sensitivity cardiac troponin (hs-cTn) T and I assays. However, variation in analytical performance between sample types precludes the interchangeable use of serum and plasma in the clinical management of a patient. This is especially true for hs-cTn assays, with certain vendors reporting different 99th percentile upper reference limits based on sample type. The International Federation of Clinical Chemistry and Laboratory Medicine provides a comprehensive summary of acceptable collection containers and sample types for contemporary and hs-cTn assays.
A review of test menus from clinical labs across the United States shows that most labs are using lithium heparin plasma for hs-cTn T and I assays.
What are the benefits of using plasma versus serum?
Plasma offers several advantages over serum. Plasma specimens can improve turnaround times from time of collection to time of result upload to a patient’s medical record since they can be immediately processed and tested expeditiously upon receipt. This is because collection of anticoagulated blood eliminates the 30-60 minutes required for clot formation for isolation of serum. Rapid turnaround times for troponin assays are key for effective and efficient assessment, management, and triage of patients with acute chest pain in the emergency department or critical care settings.
Clotting time in serum may be prolonged in patients on anticoagulation therapy, leading to delayed clotting and downstream analytical issues. Additionally, incomplete clot formation may occur in serum, resulting in the presence of microclots, which can obstruct analytical probes used in automated testing platforms.
What do labs need to consider when switching to plasma-based troponin testing?
There are several operational and clinical considerations when changing from serum to plasma for troponin assays. Changing sample type or introducing a new collection tube for troponin, such as a lithium heparin gel separator tube, can alter preanalytical workflows and laboratory practice. Laboratory workflows developed for troponin testing using plasma may also differ from those previously used for serum and from pre-existing workflows for analytes already measured in plasma, including blood gases, ammonia, and hemoglobin A1c.
Laboratory personnel will need to discuss automated versus manual processing, hand delivery versus automated routing, and aliquot versus primary container analysis to determine the most efficient sample workflow within the laboratory. Laboratories with automation capabilities may opt for an automated workflow, but this may result in longer turnaround times compared to a manual approach, depending on the instrument configuration and specimen volume. A manual approach, on the other hand, requires effective communication between the preanalytical and analytical areas and sufficient staffing to ensure proper handling and transport of specimens. When deciding between these two options, the laboratory should perform internal laboratory timing studies to develop streamlined workflows that expedite result reporting. Staffing, lab automation, specimen volume, turnaround time, and patient care goals should all be considered and ultimately guide these decisions.
In general, individual labs within a large health system with standardized processes, documents, and test menus will need to consult with stakeholders from other sites prior to changing the specimen type. Lack of harmonization for troponin is not uncommon across a healthcare system, but labs should aim for standardization of assay and sample type to mitigate interpretive challenges and maintain continuity of care. These considerations are particularly important if patients are transferred or seen at multiple clinics or locations within a healthcare system.>
Lastly, with the expected turnaround time improvements, quality assurance practices should include monitoring the troponin turnaround time before and after switching sample types. As more hospitals implement the European Society of Cardiology algorithms, labs measuring troponin in serum should strongly consider using plasma to achieve the turnaround times necessary for rapid rule in or rule out of myocardial infarction.
Kyana Garza, PhD, DABCC, is the director of clinical chemistry and point-of-care testing at Los Angeles General Medical Genter. +Email: [email protected]