Content area
Full Text
* Context.-Proper diagnosis and therapy of fibrinogen deficiency requires high-quality fibrinogen assays.
Objective.-To assess the interlaboratory bias, precision, and grading of fibrinogen assays used by laboratories participating in the United States College of American Pathologists proficiency testing program in coagulation.
Design.-Two identical vials of normal plasma were sent to more than 3500 laboratories. Participants measured fibrinogen levels using local methods.
Results.-Fifty different fibrinogen methods were evaluated. All-method bias was 8.3% (range of method-specific biases, 0.0%-27.0%) and all-method coefficient of variation was 7.7%(range ofmethod-specific coefficients of variation, 0.7%-25.8%). After controlling for reagent/instrument type, mean fibrinogen levels were 11.6% higher for prothrombin time-based reagents compared to Clauss (P < .001), and coefficient of variation was 46% lower for mechanical endpoint instruments compared to photo-optical. Most testing events (97.4%) could be reliably graded as pass or fail using a target range of ±20% from the method mean (total pass rate, 98.8%). Total fail rate was 3.0-fold lower for mechanical instruments compared to photo-optical (0.5% versus 1.5%, P = .001). Nonetheless many photo-optical methods had very high precision and very low fail rates.
Conclusions.-Fibrinogen assays showed highly variable methodology and performance characteristics. Bias, precision, and grading were affected by the type of reagent or instrument used.
(Arch Pathol Lab Med. 2012;136:789-795; doi: 10.5858/ arpa.2011-0322-OA)
Fibrinogen deficiency is an important risk factor for bleeding,1-3 and can be acquired or inherited. Acquired deficiency is most common and causes include disseminated intravascular coagulation,4 liver disease,5 hemodilution, 6 and acquired dysfibrinogenemia.7 Inherited deficiency is caused by mutations of the fibrinogen Aa, Bb, or g gene that result in quantitative or qualitative defects.8 Fibrinogen activity levels are important in the diagnosis or management of these conditions, particularly in guiding transfusion therapy with cryoprecipitate or fibrinogen concentrate.2,3,9
The first goal of this study was to determine the interlaboratory bias and precision of contemporary fibrinogen activity assays used by a large number of laboratories, and to correlate these parameters with assay variables (reagent type, instrument type, reagent/instrument type). The second goal was to grade the performance of individual laboratories as pass or fail using methodspecific peer group data, and to correlate grading with bias, precision, and assay variables. This was done using external quality assurance data obtained from participants of the 2008 College of American...