title: Serum cystatin C is sensitive to small changes in thyroid function.
abstract: BACKGROUND
  Serum cystatin C (CysC) is a novel marker for kidney function. The impact of mild thyroid dysfunction on CysC has never been investigated.
  
  
  METHODS
  CysC was determined at the time of diagnosis of subclinical hypo- and hyperthyroidism, and when TSH returned into the normal range in 40 consecutive patients with mild thyroid dysfunction.
  
  
  RESULTS
  Twenty-six patients with subclinical hypothyroidism and 14 patients with subclinical hyperthyroidism were included. In patients with subclinical hypothyroidism median (range) TSH was 7.8 (4.3-26.7) mU/l (reference 0.27-4.2) at diagnosis and decreased to 2.3 (0.36-4.0) mU/l following treatment with levothyroxine. Mean (+/-S.D.) CysC increased from 0.88+/-0.23 mg/l (reference 0.63-1.33) in the hypothyroid state to 1.01+/-0.21 mg/l when TSH normalized (p<0.001). In patients with subclinical hyperthyroidism, median TSH at diagnosis was 0.08 (0.001-0.26) mU/l and increased to 1.6 (0.28-4.0) mU/l in the euthyroid state. CysC declined from 1.04+/-0.29 mg/l at diagnosis of subclinical hyperthyroidism to 0.91+/-0.25 mg/l when TSH normalized (p<0.05).
  
  
  CONCLUSIONS
  Mild thyroid dysfunction significantly alters CysC levels. Therefore, thyroid function has to be considered when CysC is used as a marker of kidney function.
authors.affiliation: Department of Internal Medicine, University Hospital of Zurich, CH-8091 Zurich, Switzerland. peter.wiesli@dim.usz.ch
authors.forename: Peter
authors.initials: P
authors.lastname: Wiesli
authors.forename: Beat
authors.initials: B
authors.lastname: Schwegler
authors.forename: Giatgen A
authors.initials: GA
authors.lastname: Spinas
authors.forename: Christoph
authors.initials: C
authors.lastname: Schmid
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D055316:Cystatin C; D015891:Cystatins / Q000097:blood*; D005260:Female; D006801:Humans; D006980:Hyperthyroidism / Q000097:blood* / Q000175:diagnosis / Q000503:physiopathology*; D008297:Male; D008875:Middle Aged; D013960:Thyroid Function Tests; D013961:Thyroid Gland / Q000503:physiopathology*
chemical_list: C525030:CST3 protein, human; D055316:Cystatin C; D015891:Cystatins