Table 1.

NHANES III participants who met inclusion criteria. Comparison of those selected for analysis with those excluded on the basis of missing biochemical data for clearance calculationsa

ParameterExcludedIncludedP
a Data are mean (standard error [SE]) for continuous variables and proportions (SE) for discrete variables. Missing data: all variables had 98.6% or more complete information. P values for proportions were assessed by χ2 test, and for continuous variables with t test for independent samples.
n36513,251
Age
    20 to 39 yr53.6% (4.3)48.4% (1.0)0.2
    40 to 59 yr20.0% (3.1)31.9% (0.5)<0.01
    60 to 79 yr21.1% (2.1)17.1% (0.7)0.08
    ≥80 yr5.4% (1.5)2.6% (0.8)0.03
Gender (women)49.9% (4.2)51.9% (0.4)0.6
Race (black)19.1% (2.0)11.0% (0.2)<0.001
Past medical history
    hypertension22.8% (3.2)21.9% (0.7)0.7
    myocardial infarction6.6% (1.3)2.7% (0.3)0.005
    stroke1.2% (0.6)1.4% (0.2)0.80
    congestive heart failure3.1% (1.0)1.5% (0.1)0.15
    smoking (ever)52.6% (3.3)54.7% (0.8)0.53
    kidney stones6.8% (2.7)5.4% (0.4)0.65
Systolic BP (mmHg)122 (1.2)121 (0.4)0.33
Diastolic BP (mmHg)73 (0.9)74 (0.2)0.46