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Updated: Aug 12, 2026
Measurement of Factor V Activity in Human Plasma Using a Microplate Coagulation Assay
Published on: September 9, 2012
Common units for clotting factors assayed against different standards
Insights
Standardizing clotting factor measurements is crucial. A population-based method proved most effective for deriving conversion values for factors V, VII, and VIII, ensuring consistent results across different assay standards.
Area of Science:
- Hematology
- Clinical Chemistry
- Epidemiology
Background:
- Clotting factor measurements lack universally accepted units, with results often expressed as percentages relative to variable standards.
- This variability complicates the comparison of clotting factor levels across different studies and laboratories.
Purpose of the Study:
- To develop and compare methods for deriving conversion values to standardize measurements of clotting factors V, VII, and VIII.
- To establish a reliable method for routine use in large cohort studies like the Northwick Park Heart Study.
Main Methods:
- Compared three methods for deriving conversion values: standard-to-standard assay, reference plasma spanning standards, and a population-based (epidemiological) approach.
- The population-based method utilized data from over 3000 participants, adjusting for factors like age and obesity to ensure comparability.
- All results were standardized to the first assay standard (71/11) used during the six-year study period.
Main Results:
- All three methods yielded comparable results for deriving conversion values.
- The population-based method demonstrated superior performance for standardizing measurements of factors V, VII, and VIII.
- This epidemiological approach proved most satisfactory for ensuring consistency in clotting factor level reporting.
Conclusions:
- A population-based method is highly effective for standardizing clotting factor measurements, particularly when multiple assay standards are used over time.
- This approach addresses the challenge of variable standard potencies and facilitates more accurate comparisons of factor levels.
- The validated population method has been adopted for routine use, enhancing the reliability of clotting factor data in large-scale studies.
Abstract:
There are no generally accepted units for clotting factors except factor VIII. Results are usually expressed as percentages of the standards used in the assays and standards vary in their potency. Over a six year period, factors V, VII and VIII were measured in over 3000 participants in the Northwick Park Heart Study. Six different standards had to be used. For comparative purposes, all results were expressed in terms of the first standard (71/11). This paper describes how appropriate conversion values were derived. Three different methods were compared. One consisted of the assay of each standard against its replacement. Another was based on the use of a reference plasma spanning the use of two successive standards. The third was a population-based, or epidemiological method using the data from all the participants in the study. This method is based on the assumption that results would be the same in comparable groups of study participants. In order to ensure comparability, personal characteristics which affect clotting factor levels, such as age and degree of obesity, were taken into account. The three methods gave similar results but the population method was, in general, the most satisfactory for factor VIII as well as factors V and VII, and has been adopted for routine use.
