Why are blood tests for HGH claimed to be ineffective?

NFL players distrust methods utilized by the WADA. Why did the mistrust appear? Let try to understand the reason.
The World Anti-Doping Agency (WADA) decided to test players of the National Football League for HGH. Althogh the NFL Players’ Association has agreed, some skeptic thoughts linked with the grade of trustworthiness of blood test for HGH were expressed. This test is going to be just a part of the testing for anabolic steroids and other performance-enhancing drugs.
Certain experts that are not connected with the WADA activity directly do not agree with the methods utilized by this agency. They support the skepticism of the NFL players.
Matt Chaney, a chief chronicler of administration of steroids in American football, assures that the NFL players distrust the WADA anti-doping tests not without any reason. The point of view of the players is justified by Matt Chaney.
Don Catlin, the director of Anti-Doping Research, points out that methods of the WADA for detection of HGH have to be transparent. The WADA uses the HGH isoform ratio test introduced by Christian Strasburger.
It is necessary to notice that according to some specialists, the HGH isoform ratio test doesn’t have scientific basis. It is not trustworthy. The Director of Anti-Doping Research notes that this test is not useful for detection of HGH at all.
There is another test that can be utilized by the WADA to identify sportspersons who take HGH. Sonksen introduced a certain HGH testing method that is based on physiological biomarkers. But the WADA doesn’t utilize this method to identify consumers of HGH.
According to Sonksen, employees of the WADA are not specialists in this area. That’s why they do not see the priority of one method over the other. But as it was proved by experts, the HGH biomarker test is better than HGH isoform test.
Although scientists point out about difference between these two tests, the WADA doesn’t desire to to use the method elaborated by Sonksen.