Objectives: Recently it has been suggested that serum beta-N-acetylhexosaminidase (Hex) could be a joint destruction marker in rheumatoid arthritis (RA) patients. However, a large amount of serum Hex activity has its source from platelets, and the blood platelet-count is often increased in RA, which may have masked the significance of the results. The purpose of this study was to investigate the relationship between plasma activity of Hex and disease activity or severity.
Design and methods: In 51 patients with RA, with an evolution period for the illness of 10.9 +/- 1.2 yr (range 1-40 yr), we determined the total Hex activity together with its Hex A and B isoenzymes in plasma and in mononuclear (MN) and polymorphonuclear (PMN) leukocytes.
Results: The plasma activity of total Hex and Hex B isoenzyme was slightly higher in the group of patients studied (p < 0.01), together with the specific activity of total Hex, Hex A and B in PMN leukocytes (p < 0.001) than in the control group. No significant correlation was found between plasma or leukocyte Hex and the radiologic evaluation of the disease (Sharp's modified method), or the patient's functional capacity (modified Health Assessment Questionnaire). Likewise, a significant correlation between Hex activity and laboratory inflammation markers (C reactive protein, sialic acid, erythrocyte sedimentation rate) or the evolution time of the disease was not found.
Conclusions: The plasma activity of total Hex, or even of its isoenzymes Hex A and Hex B, does not appear to be a reliable marker of erosion and cartilage degradation in RA patients. Liver function appears to be the major determinant for the plasma Hex activity in these patients.