Circulating levels of sialic acid and glycosaminoglycans: a diagnostic test for ankylosing spondylitis.

The circulating levels of sialic acid (N-acetylneuraminic acid) and glycosaminoglycans (GAGs) were measured in 69 patients with spinal disorders of orthopaedic interest (ankylosing spondylitis 17, osteofluorosis 6, idiopathic backache 10, osteoarthrosis 16, osteoporosis 20). The serum GAG levels showed no statistically significant change from control values in the five disorders investigated in the present study. Although osteoporosis and osteoarthrosis showed a decrease in serum sialic acid (SA) levels, the mean ratio (SA/GAG) demonstrated no change from control values. Idiopathic backache showed no difference in any of the parameters studied when compared with control values. Ankylosing spondylitis and osteofluorosis had a remarkable similarity in their clinical and radiological features, but a divergent mean value of ratio was noted. The mean ratio of both the conditions also showed a statistically significant difference from the control value. This suggests that the SA/GAG ratio can be used as a diagnostic test in ankylosing spondylitis.