I was detected with syphilis 3.5 months ago. I had a test for LUES. It was 1:16. After 3 months it is 1:4. What does this mean? How is the drop four fold understood.
Four-fold means a 4 times change in the titer. In your example, a 1:16 decrease to 1:4 is a 4-time or 4-fold change. So look at the denominator and see if it is 4 times different. Again in your case 4 x 4 = 16.