DESCRIPTION

Secreted Frizzled Related Protein 1 (SFRP1) belongs to the SFRP family that contains a cysteine-rich domain homologous to the putative Wnt-binding site of Frizzled proteins. SFRP1 has been classified as a tumor suppressor gene due to the loss of expression in various human cancers, which is mainly attributed by epigenetic inactivation via DNA methylation or transcriptional silencing by microRNAs. SFRP1 is a biomarker for aggressive subgroups of human gastric cancer and loss of SFRP1 expression is associated with poor prognosis in hepatocellular carcinoma. Patients with high SFRP1 expression in tumor tissue had a significantly better overall survival rate, and SFRP1 can be used as a prognostic biomarker for patients with poor survival.

PRINCIPLE OF THE ASSAY

Sandwich ELISA structure (Detection antibody labeled with HRP) A capture antibody is pre-coated onto the bottom of wells which binds to analyte of interest. A detection antibody labeled with HRP also binds to the analyte. TMB acts as the HRP substrate and the solution color will change from colorless to blue. A stop solution containing sulfuric acid turns 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 20 times on one plate to assess intra-assay precision. Inter-assay Precision (Precision between assays) Three samples of known concentration were tested in 24 separate assays to assess inter-assay precision.

Intra-assay Precision

Sample	n	Mean (ng/mL)	SD	CV%
1	20	6.8	0.3	5.2
2	20	1.5	0.1	5.8
3	20	0.7	0.03	4.9

Inter-assay Precision

Sample	n	Mean (ng/mL)	SD	CV%
1	24	7.6	0.3	4.5
2	24	1.7	0.2	9.2
3	24	0.7	0.1	9.5

RECOVERY

The recovery of human SFRP1 spiked to three different levels throughout the range of the assay in various matrices was evaluated.

Sample Type		Average% of Expected	Range (%)
Human plasma	1:2	102	94-111
	1:4	112	100-123

LINEARITY

To assess the linearity of the assay, human serum samples were diluted with the appropriate Sample Diluent to produce samples with values within the dynamic range of the assay.

		Human serum
1:2	Average% of Expected	100
	Range (%)	-
1:4	Average% of Expected	108
	Range (%)	99-121
1:8	Average% of Expected	105
	Range (%)	98-118
1:16	Average% of Expected	123
	Range (%)	123-123

CALIBRATION

This immunoassay is calibrated against a highly purified recombinant human SFRP1 produced at Sunlong Medical™.