Guthrie test came back "abnomal" for cystic fibrosis

Has anyone else experienced this? My baby is 3.5 weeks and we just got the results of his blood test from the hospital where they pricked his heel after birth. We're told its "abnormal" for cyclic fibrosis and requires further testing. Well...reading into it more this test had a 90% false positive rate. CF does not run in either of our families and our little guy is showing zero symptoms. No breathing issues, normal stools, and is putting on weight like crazy (more than 2 pounds in 3 weeks). I also read the test can come back positive if there was a stressful delivery (he had the cord around his neck and was vacuumed out). Just wondering if anyone else had this result and what happened. We go in for further testing on Wednesday.