title: The impacts of thyroid function on the diagnostic accuracy of cystatin C to detect acute kidney injury in ICU patients: a prospective, observational study.
abstract: BACKGROUND
  Cystatin C (Cysc) could be affected by thyroid function both in vivo and in vitro and thereby may have limited ability to reflect renal function. We aimed to assess the association between Cysc and thyroid hormones as well as the effect of thyroid function on the diagnostic accuracy of Cysc to detect acute kidney injury (AKI).
  
  
  METHODS
  A total of 446 consecutive intensive care unit (ICU) patients were screened for eligibility in this prospective AKI observational study. Serum Cysc, thyroid hormones and serum creatinine (Scr) were measured upon entry to the ICU. We also collected each patient's baseline characteristics including the Acute Physiology and Chronic Health Evaluation II (APACHE-II) score. The diagnostic performance of Cysc was assessed from the area under the receiver operator characteristic curve (AUC) in each quartile of thyroid hormone(s).
  
  
  RESULTS
  A total of 114 (25.6%) patients had a clinical diagnosis of AKI upon entry to the ICU. The range of free thyroxine (FT4) value was 4.77 to 39.57 pmol/L. Multivariate linear regression showed that age (standardized beta = 0.128, P < 0.0001), baseline Scr level (standardized beta = 0.290, P < 0.0001), current Scr (standardized beta = 0.453, P < 0.0001), albumin (standardized beta = -0.086, P = 0.006), and FT4 (standardized beta = 0.062, P = 0.039) were related with Cysc. Patients were divided into four quartiles based on FT4 levels. The AUC for Cysc in detecting AKI in each quartile were as follows: 0.712 in quartile I, 0.754 in quartile II, 0.829 in quartile III and 0.797 in quartile IV. There was no significant difference in the AUC between any two groups (all P > 0.05). The optimal cut-off value of Cysc for diagnosing AKI increased across FT4 quartiles (1.15 mg/L in quartile I, 1.15 mg/L in quartile II, 1.35 mg/L in quartile III and 1.45 mg/L in quartile IV).
  
  
  CONCLUSIONS
  There was no significant impact of thyroid function on the diagnostic accuracy of Cysc to detect AKI in ICU patients. However, the optimal cut-off value of Cysc to detect AKI could be affected by thyroid function.
authors.forename: Feilong
authors.initials: F
authors.lastname: Wang
authors.forename: Wenzhi
authors.initials: W
authors.lastname: Pan
authors.forename: Hairong
authors.initials: H
authors.lastname: Wang
authors.forename: Yu
authors.initials: Y
authors.lastname: Zhou
authors.forename: Shuyun
authors.initials: S
authors.lastname: Wang
authors.forename: Shuming
authors.initials: S
authors.lastname: Pan
mesh_terms: D058186:Acute Kidney Injury / Q000097:blood* / Q000175:diagnosis*; D000368:Aged; D000369:Aged, 80 and over; D015415:Biomarkers / Q000097:blood; D055316:Cystatin C / Q000097:blood*; D005260:Female; D006801:Humans; D007362:Intensive Care Units / Q000639:trends*; D007677:Kidney Function Tests / Q000379:methods; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D013960:Thyroid Function Tests / Q000379:methods; D013961:Thyroid Gland / Q000502:physiology*; D013974:Thyroxine / Q000097:blood
chemical_list: D015415:Biomarkers; D055316:Cystatin C; D013974:Thyroxine