Colloidal gold reagents have experienced rapid development in the field of medical testing due to their fast, convenient, and intuitive result determination without requiring special equipment, particularly in point-of-care diagnosis and home use. There are many manufacturers of such products with wide variations in size and product quality.
It is applicable to in vitro diagnostic reagents (kits) based on the principle of antigen-antibody reaction using colloidal gold immunochromatography for qualitative detection under the category II management of in vitro diagnostic reagents registration and management method. The term "qualitative" refers to the provision of only two possible results: negative or positive.
The technical requirements for the colloidal gold method testing should comply with the relevant provisions of the in vitro diagnostic reagents registration and management method and the guiding principles for the compilation of medical device product technical requirements. The performance index of the reagent (kit) mainly includes: appearance, membrane strip width, liquid migration speed, minimum detection limit (analytical sensitivity), specificity, reproducibility, batch-to-batch variation, etc. The test method should clearly indicate the reference/control products, sample preparation method, batch and quantity of the reagent used, test frequency, calculation method. The following are some key performance indicators:
The detection limit is a key indicator of qualitative diagnostic test reagents (kits), and the concentration point selected should be in line with the clinical significance of actual diagnosis. In order to avoid excessive false positive results in clinical applications, companies should not set the concentration difference between the detection limit and the actual cutoff value too high. When evaluating this indicator, it is necessary to verify not only the positivity rate of the detected limit concentration point, but also the compliance of the negative reference product.
Conduct cross-reactivity studies on other related antibody sera with similar antigen structures or clinically similar symptoms. The applicant should submit information on all pathogens used for cross-reactivity verification and concentration confirmation, etc.
Detect common endogenous interference substances in the samples using the colloidal gold method testing, such as hemolysis, hyperlipidemia, jaundice, etc., and determine the acceptable limits of interference substance concentration by evaluating the preparation method and interference experiment of the sample.
When testing the reproducibility index of the colloidal gold method, it is recommended to use samples near the cutoff value for multiple tests, and then calculate the results or precision of multiple tests on the same sample. When analyzing the reproducibility of the reagent, strongly positive or obviously negative samples should not be used, otherwise the detection effect cannot be objectively evaluated.
Select three batches of test strips, take the same amount from each batch, operate according to the instructions and test for reproducibility. The results of the three different batch tests should be consistent, and the color density should be uniform.