Thus, intrathecal production of CXCL13 (IPCXCL13) can be estimated by the use of the CXCL13 index (QCXCL13/Qalbumin) in a similar manner to how the IgG index (QIgG/Qalbumin), a commonly used measure in clinical assessment of MS patients [49], estimates intrathecal production of IgG. Here, CXCL13 is linked to myeloid sarcoma.