The kit assay may work for biological fluids assuming that the analyte being measured is present above the limit of detection for the kit after any sample preparation (if required). Centrifugation of the samples and use of the supernatant directly in the kit assay (with appropriate dilution in distilled water) may be sufficient. However, if a more stringent sample preparation method is required examples are provided in this document "Biological Samples".
The test kit may not have been tested using biological fluids as samples because it is not marketed or registered as a medical device. Therefore this will require your own validation.