VDL Investigates Problems with PRRSv Antibody Test Kit for Oral Fluids

March 30, 2017

Testing oral fluids for antibodies to Porcine Respiratory and Reproductive virus (PRRSv) is an efficient and effective way to monitor swine herds for exposure to this devastating virus. The VDL uses commercially manufactured kits for this testing.

In March 2017, Idexx reported that recent lots of PRRSV antibody test kit for oral fluids manufactured in the United States may have lower specificity producing occasional weak positives that run close to the assay cutoff (i.e. that do not confirm as true positives).

The Serology lab at the VDL had been using one of these lots (lot number FM336).  The VDL ordered another kit lot (lot number H571) manufactured by Idexx, Europe. A total of 45 samples that were tested by lot number FM336 were re-tested using the new lot (H571).  Out of these, 32 samples that had S/P (sample to positive) ratio that were close to cut off in lot FM336 were found negative in lot number H571. Thirteen samples were positive in both lots; these 13 samples had S/P ratios greater than 2.0 when initially tested by lot FM336. On kit lot H571, these 13 samples had S/P ratios in the positive range, although the numbers were lower than those obtained by lot FM336.  (See table below)


PRRS OF kit lot number

No. positive

No. negative

FM336 (US)



H571 (Europe)




The VDL has immediately stopped using lot number FM336 and switched to testing by lot number H571.

In order to continue monitoring the specificity of the test, clients are asked to indicate expected PRRS status (positive or negative) of their farms on the swine health test chart when submitting samples. This will help determine if any samples need to be re-tested.

picture of swine health test chart