This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Misc. (W.B.C), Subject name: Pathology
[{'content': 'The single most important predictor of survival in multiple myeloma \nSelect and explain. \nA. IL-6 levels, B. Bence jones proteinuria, C. CD 138 positivity, D. Serum b2-microglobulin', 'role': 'user'}, {'content': 'Answer: D \nExplanation: Ans. (d) Serum b2 -microglobulin(Ref: Robbins 9th/pg 598-602/8th 608-612)b2-M concentration is the strongest and most reliable prognostic factor for multiple myeloma. It depends not only on tumor burden but also on renal function. Elevated b2-M values predict early death', 'role': 'assistant'}]