A Review of Factor VIII and Factor IX Assay Methods for Monitoring Extended Half-Life Products in Hemophilia A and B

Clinical trials have used a variety of coagulation factor assay methods to assess treatment with recombinant Factor VIII (rFVIII) and recombinant Factor IX (rFIX) extended half-life (EHL) products. However, diagnostic laboratories may use different reagent combinations for routine use or for field trials of EHL products. The focus of this review is on the choice of one-stage clotting and chromogenic Factor VIII and Factor IX methods and the influence that assay principle and components may have on results, including the effects of different activated partial thromboplastin time reagents and factor-deficient plasma. Our aim is to tabulate the findings for each method and reagent group to give laboratories practical guidance as to how the reagent combinations used in their local laboratory compare to others, for the various EHLs available.

An Analysis of the Sensitivity of the Activated Partial Thromboplastin Time (APTT) Assay, as Used in a Large Laboratory Network, to Coagulation Factor Deficiencies

OBJECTIVES

To advance knowledge in using the ex vivo method to identify factor sensitivity of the activated partial thromboplastin time (APTT), using data from a hemophilia and reference hemostasis laboratory; to evaluate application of inclusion and exclusion criteria to eliminate data outliers; and to discuss outcomes with reference to comparable studies.

METHODS

An ex vivo, retrospective analysis was performed on patient samples with conjointly ordered APTT and intrinsic pathway factors (VIII, IX, XI, XII) for application to a large network of laboratories. The relationship between factor levels and APTT, before and after application of exclusion criteria, is demonstrated.

RESULTS

Curvilinear relationships were found between all factor levels and APTTs, which demonstrated both similarities and differences with available studies. Factor sensitivity data are presented. Study strengths include large sample size and use of real-world data. Limitations include inability to exclude all residual outliers and paucity of patient samples singularly deficient in factors other than FVIII.

CONCLUSIONS

This ex vivo, retrospective analysis of the sensitivity of the APTT assay to intrinsic pathway factor deficiencies using real-world data from a hemophilia and reference hemostasis laboratory contains the largest sample size using this approach to date. The outcomes assist in informing practice in this area and can be used as a reference for further studies.

Estimation of Measurement Uncertainty of Factor Assays Using the Monte Carlo Simulation

OBJECTIVES

We aimed to quantify the measurement uncertainty (MU) for factor activities using the Monte Carlo simulation (MCS), which is a computational algorithm that simulates statistical sampling to obtain numerical results through complex mathematical calculations.

METHODS

The uncertainties of factor V (FV), factor VIII (FVIII), and factor X (FX) were simulated with two coagulation testing systems: ACL TOP 750 CTS (Instrumentation Laboratory) and STA Compact (Diagnostica Stago).

RESULTS

When the factor activities were 74% (FV), 68% (FVIII), and 89% (FX), the MUs were 3.5% (FV), 9.3% (VIII), and 2.8% (FX) for ACL TOP and 8.5% (FV), 18.2% (FVII), and 6.5% (FX) for STA Compact. MCS MUs were compared with MUs obtained from running actual samples (not simulated) using a method called the top-down approach. The MCS MU results were interchangeable with MUs from the top-down approach, except for FVIII from STA Compact.

CONCLUSIONS

The MCS procedure is well suited for the quantification of MUs for factor assays over the entire measurement range.

Rare bleeding disorders: spectrum of disease and clinical manifestations in the Pakistani population

Background

Rare inherited coagulation factor deficiencies constitute an important group of bleeding disorders. A higher frequency of these disorders is seen in areas of high consanguinity. Our aim was to study the prevalence and spectrum of rare inherited bleeding disorders, characterize the severity of the deficiencies, identify different clinical manifestations, and evaluate different treatments provided.

Methods

This cross-sectional study was conducted in the Department of Haematology, Armed Forces Institute of Pathology Rawalpindi, between January 2014 and December 2018. A detailed history was taken, and an examination was performed. The signs and symptoms were noted, and the patients were diagnosed on the basis of a coagulation profile. The disease severity was assessed using factor assays.

Results

Among 2,516 patients with suspected coagulation disorders, 774 (30.8%) had an inherited bleeding disorder. Of the 774 patients, 165 (21.3%) had a rare bleeding disorder; 91 (55.2%) of them were males, and 74 (44.9%) were females, with a male-to-female ratio of 1.2:1. The median patient age was 9 years 3 months. The most common disorder was factor VII deficiency (46 patients, 27.9%). The most common clinical presentation was bruising in 102 (61.8%) and gum bleeding in 91 (55.2%) patients.

Conclusion

The most common rare bleeding disorder in our population is factor VII deficiency. The prevalence of these bleeding disorders is high in our population due to a high number of consanguineous marriages.