Brief observations
Autoantibodies against carbonic anhydrase II are increased in renal tubular acidosis associated with Sjögren syndrome

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Methods

We measured levels of anti-carbonic anhydrase II antibody in serum samples from 46 patients who had been diagnosed with primary Sjögren syndrome and who were followed regularly in our outpatient clinic. The diagnosis of Sjögren syndrome required at least four of six standard criteria. 11 No patients had hypocomplementemia or anti-DNA antibodies.

Distal renal tubular acidosis was diagnosed if the arterial bicarbonate level was <22 mEq/L at baseline and the fasting urine pH was >5.5. 12 Ten

Results

Of the 46 patients with primary Sjögren syndrome, 13 were diagnosed with distal renal tubular acidosis, including 7 who underwent the ammonium chloride loading test (Table 1). Patients with distal renal tubular acidosis had lower serum levels of bicarbonate and potassium, and higher urine pH, than did patients in the group without renal tubular acidosis. They also had higher levels of serum creatinine, γ-globulin, immunoglobulin G, anti-Ro/SSA, and anti-La/SSB; a longer duration of disease;

Discussion

We found that among patients with Sjögren syndrome, those with distal renal tubular acidosis had higher levels of anti-carbonic anhydrase II antibody than did those without renal tubular acidosis, although there was some overlap in antibody levels. Although our results cannot establish a causal relation, disordered function of carbonic anhydrase II may be involved, since patients with congenital carbonic anhydrase II deficiency have presented with renal tubular acidosis. 16, 17

It is not known

Acknowledgment

We are grateful to Drs. Hiroshi Kanbayashi and Yuzo Endo for their useful suggestions.

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