Following the standard order of draw, which tube is collected immediately after the light blue sodium citrate tube?

Explanation

The standard order of draw is blood cultures, light blue citrate, red or gold serum tubes, green heparin, lavender EDTA, and finally gray fluoride or oxalate, so the serum tube follows the citrate tube. Blood cultures always come first to protect sterility. Drawing lavender or gray tubes too early risks carrying additives such as EDTA or potassium into later tubes and skewing results.