Negative for a uti. no leukocytes from dipstick analysis. semen is yellow. lab sent my urine to check for std. could i have an std still even with no leucocytes in urine?

Yes, you can. The "leukocyte" in urine dipstick is not detecting leukocytes (white blood cell) , actually leukocyte esterase released from broken-down leukocytes.

Dipstick test are not for STD but to get an idea of possibility of infection in urine and can be false positive/neg.. Yes - tho rare one can have an STI without the urine being positive for Leuco