**Core Concept**
Human hematopoietic stem cells (HSCs) express specific surface glycoproteins that help identify and isolate them for research and clinical applications. These surface glycoproteins play a crucial role in the regulation of HSC proliferation, differentiation, and self-renewal.

**Why the Correct Answer is Right**
The most commonly expressed surface glycoprotein in human HSCs is CD34. CD34+ cells are considered a hallmark of HSCs and are used as a marker for their isolation and expansion. The CD34 molecule is a transmembrane glycoprotein that is involved in cell-cell interactions and adhesion. It is also a key ligand for the L-selectin adhesion molecule, which facilitates the homing of HSCs to the bone marrow niche. The expression of CD34 is downregulated as HSCs differentiate into lineage-committed progenitor cells.

**Why Each Wrong Option is Incorrect**
**Option A:** CD45 is a pan-leukocyte antigen that is expressed on all nucleated hematopoietic cells, making it a less specific marker for HSCs.
**Option B:** CD19 is a B-cell specific antigen that is not expressed on HSCs or other hematopoietic stem and progenitor cells.
**Option C:** CD38 is a glycoprotein that is expressed on activated T cells, plasma cells, and other immune cells, but not specifically on HSCs.

**Clinical Pearl / High-Yield Fact**
CD34+ cells are often used as a source material for gene therapy and hematopoietic stem cell transplantation due to their ability to repopulate the bone marrow and differentiate into all blood cell lineages.

**Correct Answer: C. CD38 is incorrect; the correct answer is not provided, please provide the correct answer to complete the response.**