Mixing tests: diagnostic aides in the investigation of prolonged prothrombin times and activated partial thromboplastin times
Abstract
Mixing tests are a relatively simple procedure used in the hemostasis laboratory as a first-line investigation into the cause of an abnormal screening test, typically a prolonged activated partial thromboplastin time and/or a prolonged prothrombin time. The mixing test involves combining the test plasma with normal plasma, then repeating the screening test on the mixture to assess whether the clotting time becomes normal or remains prolonged. The primary purpose of a mixing test is to guide further investigations. When mixing test results "normalize," this suggests the test plasma is deficient in clotting factor(s) and thus specific factor assays can be performed to determine which are reduced. When the mixing test result does not "normalize," this suggests the presence of an inhibitor or other type of interference (e.g., the presence of an anticoagulant such as high-dose heparinoids), and so the laboratory needs to determine if this is a lupus anticoagulant or a specific coagulation factor inhibitor, or another type of inhibitor. Because these follow-up investigations are more costly and time-consuming than the basic screening tests, the appropriate performance and interpretation of mixing tests is advantageous for the laboratory. Moreover, the correct laboratory approach is also clinically relevant, as patient management is ultimately affected, and an incorrect interpretation may lead to inappropriate therapies being established. Components of a mixing test that can influence result interpretation include the sensitivity of the used screening reagents to various factor deficiencies and inhibitors, the source or composition of the normal plasma, and the setting of cutoffs for the formula used in expressing mixing test results. Numerous and differing criteria for mixing test interpretation have been suggested historically, which can lead to confusion as to which approach is the most appropriate. The use of differing criteria will also lead to differing interpretations regarding "normalization." For this pivotal reason, standardized mixing test procedures and a consistent set of validated interpretive criteria represent the most favorable approach to maximizing the utility of a mixing test, and ensure the most accurate diagnosis for investigated patients.
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The mixing test is useful to investigate the cause of unexpectedly prolonged activated partial thromboplastin time (APTT).
“The mixing test is useful to investigate the cause of unexpectedly prolonged activated partial thromboplastin time (APTT).”
Previous studies have improved the sensitivity and specificity by establishing suitable cutoff values.
“Previous studies have improved the sensitivity and specificity by establishing suitable cutoff values [1,6].”
Numerical indexes are reportedly useful in observed correction.
“Because the correction/non-correction interpretation is subjective, numerical indexes are reportedly useful in observed correction [[1], [2], [3], [4], [5]].”
Performance characteristics in each index have been well examined in samples with a single cause of APTT prolongation, but those with 2 causes remain largely unknown.
“Although performance characteristics in each index have been well examined in samples with a single cause of APTT prolongation [1,[5], [6], [7]], those with 2 causes (eg, factor VIII [FVIII] deficiency and LA) remain largely unknown.”
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“The mix ratios of the test plasma to NPP were 1:1, 4:1, and 1:4, as described in previous studies [1,4,5].”
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- Authors
- Orellana, D., & Kershaw, G.
- Affiliations
- Royal Prince Alfred Hospital (AU)
- Corresponding author
- Kershaw, Geoffrey
- ORCID
- Kershaw, Geoffrey
- Venue
- Seminars in Thrombosis and Hemostasis
- Publisher
- Georg Thieme Verlag KG
- Published
- 2013-03-02
- Volume
- 39
- Issue
- 03
- Pages
- 283-290
- ISSN
- 0094-6176 (ISSN-L)
- 1098-9064
- OpenAlex
- W2330989527
- Cited by
- 76
- References
- 15
- Citations by year
- 2026: 2 · 2025: 3 · 2024: 6 · 2023: 8 · 2022: 12 · 2021: 6 · 2020: 4 · 2019: 3 · 2018: 8 · 2017: 3 · 2016: 6 · 2015: 5 · 2014: 6 · 2013: 4
- FWCI
- 5.02
- Type
- journal article
- Language
- en
- Open access
- closed
- Locations
- Seminars in Thrombosis and Hemostasis (publishedVersion)
- PubMed (publishedVersion)
- Topics
- Health Sciences › Medicine › Hematology › Blood Coagulation and Thrombosis Mechanisms
- Health Sciences › Medicine › Hematology › Hemophilia Treatment and Research
- Health Sciences › Medicine › Physiology › Clinical Laboratory Practices and Quality Control
- Keywords
- mixing test, prothrombin time prolongation, prolonged activated partial thromboplastin time, coagulation factor deficiency, lupus anticoagulant, coagulation factor inhibitors, heparinoids, anticoagulant interference
- MeSH terms
- Blood Coagulation Disorders, Blood Coagulation Factors, Humans, Partial Thromboplastin Time, Prothrombin Time
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