How did this Changeling pass the blood test?

Question

In the Star Trek: Deep Space Nine episode “Way of the Warrior”, General Martok met with Benjamin Sisko and Kira Nerys aboard Deep Space Nine. Before they began the meeting, General Martok insisted on a blood test: All three characters cut their hand with Martok’s knife and dripped blood on the table. Since none of the blood reverted to changeling goo, it was assumed that all three were who they appeared to be.

This appears to be an effective way of screening changelings, and is later used to reveal one. However, we later find out that

Martok was a changeling, and had been the entire time - since before his first appearance until his death in episode Apocalypse Rising. The real Martok does not appear until the later episode Purgatory's Shadow.

Since his blood did not revert, how was this achieved?

Answer 1

According to the Star Trek: Memory Alpha there is no official explanation for what happened; bold emphasis is mine:

The changeling impersonating Martok once took a blood test, cutting himself with a d'k tahg and allowing blood to drip out of his hand in DS9: "The Way of the Warrior". It was never stated in canon how the changeling managed this, but Joseph Sisko once suggested that a way a changeling could beat the blood test was to kill a random civilian on the street, absorb the man's blood into itself and release it whenever it took part in a test. It is possible the Martok changeling did this. It could also provide an explanation as to why the Dominion kept the real people that changelings impersonated alive in Internment Camp 371.

And as explained in the summary on Star Trek: Memory Alpha for the Homefront episode:

The blood tests may not be all that infallible anyway. Joseph argues that if the Changelings are all that clever, they'll find a way around the blood screening tests telling Ben there's not a test that exists that someone smart enough can't get around.