True about smoldering myeloma is -a) Monoclonal gammopathyb) Lytic bone lesionc) Hypercalcemiad) Bone marrow plasma cell > 10%

**Core Concept**
Smoldering myeloma, a precursor to multiple myeloma, is characterized by the presence of monoclonal plasma cells in the bone marrow, but without the typical symptoms or end-organ damage seen in active multiple myeloma. This condition is associated with a higher risk of progression to multiple myeloma, and the bone marrow plasma cell percentage is a key factor in its diagnosis.

**Why the Correct Answer is Right**
The correct answer is **D) Bone marrow plasma cell > 10%**. This is because the diagnosis of smoldering myeloma requires the presence of more than 10% monoclonal plasma cells in the bone marrow, as per the International Myeloma Working Group (IMWG) criteria. This is a critical distinction from monoclonal gammopathy of undetermined significance (MGUS), which is defined by less than 10% monoclonal plasma cells in the bone marrow. The presence of more than 10% monoclonal plasma cells indicates a higher risk of progression to multiple myeloma.

**Why Each Wrong Option is Incorrect**
**Option A:** Monoclonal gammopathy is a hallmark of smoldering myeloma, but it is not exclusive to this condition and can be seen in other conditions such as MGUS or multiple myeloma itself. Therefore, this option is not specific enough for the diagnosis of smoldering myeloma.

**Option B:** Lytic bone lesions are a common feature of multiple myeloma, but they are not typically seen in smoldering myeloma. In fact, the absence of lytic bone lesions is one of the defining characteristics of smoldering myeloma.

**Option C:** Hypercalcemia is a complication of multiple myeloma, but it is not typically seen in smoldering myeloma. The absence of hypercalcemia is one of the criteria for diagnosing smoldering myeloma.

**Clinical Pearl / High-Yield Fact**
When diagnosing smoldering myeloma, it's essential to remember that the presence of more than 10% monoclonal plasma cells in the bone marrow is a critical factor. This distinction is crucial for differentiating smoldering myeloma from MGUS and for predicting the risk of progression to multiple myeloma.

**Correct Answer: D. Bone marrow plasma cell > 10%**