DESCRIPTION

Factor XI (FXI) is the zymogen of a blood coagulation protease, factor XIa (FXIa), that contributes to hemostasis by activating factor IX. Factor XI is a precursor of an S1 serine protease found in blood plasma. When activated to FXIa, it plays a crucial role in forming and stabilizing fibrin by triggering the activation of factor IX.

PRINCIPLE OF THE ASSAY

An anti-tag antibody is pre-coated onto the bottom of wells. After adding antigen or samples, Tagged-Capture antibody and HRP-conjugated detection antibody, a sandwich complex is formed in the solution. TMB acts as a HRP substrate, and the solution color will change from colorless to blue. A stop solution containing sulfuric acid turns the solution yellow. The color intensity is proportional to the quantity of bound protein, which is measurable at 450 nm with the correction wavelength set at 630 nm.

PRECISION

Intra-assay Precision (Precision within an assay) Three samples of known concentration were tested 8 times on one plate to assess intra-assay precision. Inter-assay Precision (Precision between assays) Three samples of known concentration were tested in 16 separate assays to assess inter-assay precision.

Intra-assay Precision

Sample	n	Mean (pg/mL)	SD	CV%
1	8	4,457.4	130.5	2.9
2	8	1089.7	21.7	2.0
3	8	538.6	11.5	2.1

Inter-assay Precision

Sample	n	Mean (pg/mL)	SD	CV%
1	16	4,458.9	127.0	2.8
2	16	1097.5	24.8	2.3
3	16	549.2	18.9	3.4

RECOVERY

The recovery of human Factor XI spiked to three different levels throughout the range of the assay in human plasma was evaluated.

Sample Type		Average% of Expected	Range (%)
Human plasma	1:6,400	107	107-108
	1:12,800	103	100-105

LINEARITY

To assess the linearity of the assay, samples were diluted with the appropriate Sample Diluent to produce samples with values within the dynamic range of the assay. (The human plasma was initially diluted 1:800.)

		Human plasma
1:2	Average% of Expected	100
	Range (%)	-
1:4	Average% of Expected	99
	Range (%)	95-103
1:8	Average% of Expected	97
	Range (%)	91-102
1:16	Average% of Expected	108
	Range (%)	98-118

CALIBRATION

This immunoassay is calibrated against a highly purified recombinant human Factor XI produced at Sunlong Medical™.