Table 3 Piecewise linear regression model between serum cotinine and PTH.

From: Association between tobacco smoke exposure and serum parathyroid hormone levels among US adults (NHANES 2003–2006)

Ln-cotinine(ng/dL)

Adjust OR (95% CI) P value

Fitting by linear regression model

−0.58 (−0.72, −0.45) < 0.001*

Fitting by two-piecewise linear regression model

 

Inflection point

8.29

 < 8.29

−0.25 (−0.51, 0.01) 0.0602

 > 8.29

−2.10 (−3.12, −1.08) < 0.001*

Log likelihood ratio test

 < 0.001*

  1. *p < 0.05.
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