As laboratory technology continues to advance, new assays routinely become available to help risk stratify patients and guide treatment choices.1 Globally, the clinical utility of blood assay systems is also increasing.1 Consequently, developing appropriate standardization is essential to ensure that clinical laboratories perform valid tests for anticoagulants and procoagulants as part of their routine diagnostic processes.2

The British Society for Haematology (BSH) recently published a guideline update for the laboratory aspects of assays used in hemostasis and thrombosis in the British Journal of Haematology. Peter Baker, of Oxford University Hospital’s NHS Foundation Trust in Oxford, United Kingdom, and coauthors, updated 2 previous guidelines released in 2003 and 2013.

“Adherence to national and international guidance of [laboratory] best practice [is important for clinicians]” explained Mr Baker (email communication, P Baker, June 2020).

“The three most important takeaways from the guidelines include: preanalytical variables, assay selection, and timeliness of testing,” he said.


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Best Practices

In order to minimize preanalytical errors in the clinical laboratory, the importance of procedural standards for blood collection, handling, and storage becomes evident. Both laboratory and phlebotomy staff must be properly trained, and must understand the test being performed, including potential sources of error.

In the new guidelines, Baker and his colleagues established recommendations and best practices for:

  1. Blood collection
  2. Sample handling
  3. Storage and preparation
Table. Selected Recommendations by the BSH Guideline Group for Blood Collection, Handling and Storage2
Blood collection
  • Perform clean venipuncture with minimal stasis
  • Use a 21-gauge needle (19 gauge may be used in adults with good veins, 23 gauge may be required for infants)
    • If a butterfly is used and the coagulation tube is the first tube drawn then a discard tube should be used
  • Do not use heparin-contaminated venous lines
    • Where this is unavoidable because of poor venous access, flush the line with saline and use a labelled discard tube
  • Ensure correct order of drawing (generally the coagulation tube should be the first drawn)
Sample handling
  • Whole blood samples should be transported at room temperature to the laboratory as soon as possible, within 1 hour if possible
  • Prior to centrifugation samples should be examined for correct fill and clots
  • Centrifugation and analysis should be undertaken as soon as possibleAfter centrifugation, samples should be examined for hemolysis, icterus, and lipemia
Storage and preparation
  • Most tests should be performed within 4 hours of sample collection
    • Exception: Activated partial thromboplastin time (APTT) for monitoring unfractionated heparin (UFH), which should preferably be tested within 1 hour and the prothrombin time (PT), which has a stability of 24 hours

The group also suggested that PT, APTT, and a coagulation screen should be completed on all samples referred for hemostasis assays. This practice serves as validation for sample quality, and may also identify the presence of anticoagulants, if not known from clinical evaluation.

To read the detailed recommendations containing qualifying statements, readers should refer to the full guidelines in the British Journal of Haematology.

Key Clinical Takeaways

Preanalytical variables

With respect to sample collection, Mr Baker said, “Poorly collected samples, including under filling, will give spurious results that delay patient management and eventually only lead to a need for repeat [collection and testing]. With delivery, a pre-agreed process needs to be in place for rapid predictable transport and processing of samples.

“Hemolysis, icterus, and lipemia can impact a large proportion of coagulation analyzers and should be avoided where possible,” he explained.

Assay selection and timeliness

Mr Baker stressed that clinicians need to be aware of specific test limitations, and said, “Using predefined testing panels and algorithms will reduce the need for inappropriate testing, which may only add confusion to interpretation.”

He further explained that in terms of cost, “A step wise approach should be used to rule out higher probability causes before considering rarer conditions.”

With respect to timing of testing, he recommended that “Testing during or soon after a thrombotic event, however attractive, should be avoided as it usually ends up with a need for repeat testing.”

Additionally, “Testing during anticoagulation is to be avoided where possible. Alternatively, an awareness of the impact of vitamin K antagonists and DOACs on individual assays types is [important],” he said.

Raising Awareness and Concluding Remarks

“Communication between experts, using case studies to highlight rare or unexpected outcomes [is one strategy to increase awareness about lab best practices],” Baker explained.

“[When in doubt], speak to the lab. There is a lot of expertise that they are usually more than happy to share [with clinicians].”

References

1. Brummel-Ziedins KE, Wolberg AS. Global assays of hemostasis. Curr Opin Hematol. 2014;21(5):395-403.

2. Baker P, Platton S, Gibson C, et al. Guidelines on the laboratory aspects of assays used in haemostasis and thrombosis [published online June 14, 2020]. Br J Haematol. doi: 10.1111/bjh.16776