Okay, the user wants me to translate "serum proteins" into Japanese. Let me check the rules again. The first rule says to translate all content into Japanese. The second rule states that if the content is already in Japanese, leave it as is. The third rule is to provide only the translation without any explanations.
So, "serum proteins" is in English. I need to translate it. The correct translation for "serum proteins" in Japanese is "血清タンパク質". I should make sure there's no typo. Also, since the user mentioned to output only the translation, I shouldn't add anything else. Let me confirm the term again. Yes, "血清タンパク質" is the accurate term used in medical or biological contexts. Alright, that's all. Just output that term.