Abstract Number: PB0513
Meeting: ISTH 2020 Congress
Background: The APTT is used as a screening test for deficiencies of factors VIII, IX and XI. A prolongation to the APTT should be observed when the clotting factor is below 30 IU/dL. APTT reagents may demonstrate different sensitivities to these clotting factors because of their composition.
Aims: To compare the APTT sensitivity to FVIII, IX and XI of two new APTT reagents from Horiba (Kyoto, Japan), APTT 4 and APTT Liq 4, with 6 commonly used APTT reagents.
Methods: FVIII deficient plasma (Siemens), FIX and FXI deficient plasma (Precision Biologic) was spiked with normal plasma (CCNRP, Precision Biologic) to obtain plasmas with factor concentrations of 0-90 IU/dL. APTT were performed with 8 APTT reagents on 5 different days. Local reference ranges were generated for each reagent. The intersection of the upper limit of the APTT reference range and concentration of clotting factor determined the reagent sensitivity.
Results: Sensitivity to FVIII ranged from 31.5- 67.3 IU/dL (Synthasil, Actin FS), to FIX from 15.9-36.1 IU/dL (APTT SP, Synthasil) and to FXI from 28.3-55.2 IU/dL (Actin FSL, Synthafax). Interassay CV was less than 5.5% for all reagents and factors. Sensitivity to FVIII and FXI was greater than 30 IU/dL with all reagents, including APTT 4 and APTT Liq 4, with the exception of Actin FSL and FXI (28.3 IU/dL). Sensitivity to FIX was greater than 30 IU/dL with Synthasil only.
Conclusions: A normal APTT does not always indicate normal haemostasis. The sensitivity to FVIII and FXI of most of those APTT reagents included in this study was considered acceptable however sensitivity to FIX was lower. The source of activator did not appear to effect sensitivity but the phospholipid source, type and concentration may well influence the ability to diagnose reduced factor activities, particularly FIX.
| APTT Reagent | Composition | FVIII Sensitivity(IU/dL) | FIX Sensitivity(IU/dL) | FXI Sensitivity(IU/dL) |
| Actin FS | Ellagic acid, purified soy phosphatides | 67.3 | 25.5 | 49.3 |
| Actin FSL | Ellagic acid, soy/rabbit brain phosphatides | 46.7 | 22.6 | 28.3 |
| STA-PTTA | Silica, rabbit brain phospholipid | 47.6 | 29.0 | 35.7 |
| APTT 4 | Micronised silica, rabbit brain phospholipid | 40.9 | 26.8 | 43.3 |
| APTT LIQ 4 | Ellagic acid, rabbit brain phospholipid | 37.4 | 29.7 | 48.9 |
| SYNTHASIL | Silica, synthetic phospholipids | 31.5 | 36.1 | 49.0 |
| SYNTHAFAX | Ellagic acid, synthetic phospholipids | 62.8 | 27.5 | 55.2 |
| APTT SP | Silica, synthetic phospholipids | 38.4 | 15.9 | 35.6 |
[Table 1. The senstivity of 8 APTT reagents to factors VIII, IX and XI]
To cite this abstract in AMA style:
Bowyer A, Kitchen S, Maclean R. The Sensitivity of Two New APTT Reagents to Factors VIII, IX and XI [abstract]. Res Pract Thromb Haemost. 2020; 4 (Suppl 1). https://abstracts.isth.org/abstract/the-sensitivity-of-two-new-aptt-reagents-to-factors-viii-ix-and-xi/. Accessed September 29, 2023.« Back to ISTH 2020 Congress
ISTH Congress Abstracts - https://abstracts.isth.org/abstract/the-sensitivity-of-two-new-aptt-reagents-to-factors-viii-ix-and-xi/