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Association of anion gap with thyroid dysfunction and nodular goiter in CAPD patients
Chih Ching Lin1, Wu Chang Yang, Yee Yung Ng
1Department of Medicine, Veterans General Hospital-Taipei, and School of Medicine, National Yang-Ming University, Taiwan, Republic of China.
Objective:
To investigate the association of clinical parameters and serum anion gap with thyroid dysfunction and nodular goiter in continuous ambulatory peritoneal dialysis (CAPD) patients.
Design:
Cross-sectional study.
Setting:
Single dialysis unit and outpatient clinic.
Patients:
This study Included 89 uremic patients on CAPD. Gender ratio was 50 males to 39 females (M/F = 1.28); mean age was 54.8 years.
Main Outcome Measures:
We investigated the prevalence of nodular goiter and thyroid dysfunction with a 10-MHz high-frequency ultrasound scanner and immunoassay kits.
Results:
Nodular goiter was detected in 52.8% (47/89) of the CAPD patients. Patients with nodular goiter were older than those without goiter (57.7 vs 51.5 years, p < 0.05). Nodular goiter was found more frequently in females than in males (66.7% vs 44.0%, p < 0.05). Patients with nodular goiter had longer duration of CAPD than patients without goiter (51.6 +/- 42.9 vs 31.0 +/- 28.1 months, p < 0.02). In addition, CAPD patients with goiter had a higher serum anion gap (AG) (16.8 +/- 3.3 vs 14.0 +/- 4.5 mEq/L, p < 0.02) and a lower weekly creatinine clearance (55.9 +/- 12.6 vs 64.6 +/- 21.1 L/week/1.73 m2, p < 0.05) than patients without goiter. As serum AG gradually Increased, significant alteration of thyroid parameters developed In the following sequence: (1) reduction of total T3 level at an AG level of 15, (2) elevation of thyrotropin (TSH) and Increased prevalence of goiter at an AG of 18, and (3) reduction of free T4 and total T4 levels and elevation of TSH, with further increased frequency of goiter at an AG of 20 mEq/L.
Conclusion:
According to this study, age, gender, dialysis duration, serum AG, and weekly creatinine clearance are correlated with prevalence of goiter in CAPD patients. Sequential alteration of thyroid function and Increasing frequency of nodular goiter correlated with higher serum AG. There are two explanations for this correlation: the level of serum AG may be an indirect index of the level of serum goitrogens, and higher serum AG and Increased frequency of nodular goiters might be a reflection of loss of residual renal function. Therefore, thyroid function screening and goiter detection using ultrasound should be considered when examining CAPD patients with progressively elevating serum anion gap.