Table 1 Equations used to predict 24-hour urinary sodium excretion from spot urine samples^a

Brown et al., 2013 [25]

Male (n = 241) Female (n = 2852) Aged 20–59 years

INTERSALT Men: = 23 × {25.46+[0.46 × spot NA (mmol/L)]−[2.75 × spot Cr (mmol/L)]−[0.13 × spot K (mmol/L)]+[4.10 × BMI (kg/m2)]+[0.26 × age (yr)]} Women: = 23 × {5.07+[0.34 × spot NA (mmol/L)]−[2.16 × spot Cr (mmol/L)]−[0.09 × spot K (mmol/L)]+[2.39 × BMI (kg/m2)] + [2.35 × age (yr)]−[0.03 × age2 (yr)]}

No calculation of Pr24UCr used in equation

Tanaka et al., 2002 [26]

Developed in 591 Japanese adults aged 20–59 years

Tanaka = 23 × (21.98 × XNa^0.392), where XNA = [spot Na (mmol/l)/spot Creatinine (mg/dL) × 10] × Pr24UCr (mg/day)]

Pr24UCr (mg/day) = (− 2.04 × age (year)) + (14.89 × weight (kg)) + (16.14 × height (cm)) − 2244.45

Kawasaki et al., 1993 [27]

Equation for predicted 24-h urine creatinine excretion developed in a study of 256 male and 231 female participants aged 20–79 year (41) and validated in 20 male and 27 female Japanese and foreign (including 16 American) subjects

Kawasaki = 23 × (16.3 × XNa^0.5), where XNA = [spot Na (mmol/l)/spot creatinine (mg/dL) × 10] × Pr24UCr (mg/day)

Pr24UCr (mg/day) for men = (12.63 × age (year)) + (15.12 × weight (kg)) + (7.39 × height (cm))− 79.9

Pr24UCr (mg/day) for women = (− 4.72 × age (year)) + (8.58 × weight (kg)) + (5.09 × height (cm))− 74.5

Mage et al., 2003 [28]

The Mage equation was developed to predict urine pesticide and chemical exposure with NHANES urine specimens. Equation for predicted 24-h urine creatinine excretion developed in a separate study (42) of 249 men in Canada with corrections based on the relative amounts of fat and muscle mass in women (25,43) and differences in muscle mass by race and BMI (28,44)

Mage = {[23 × spot NA (mmol/L)]/[spot Cr (mg/dL) × 10]} × [Pr24UCr (mg/day)]

Pr24UCr (mg/day) for men = 0.00179 × (140 − age (year)) − (weight (kg)^1.5 × height (cm)^0.5) × (1 + 0.18 × A × (1.366 − 0.0159 × BMI (kg/m²)) where A is African American or black race = 1, other race = 0. Pr24UCr (mg/day) for women = 0.00163 × (140−age (year)) × (weight (kg)^1.5 × height (cm)^0.5) × (1 + 0.18 × A × (1.429 – 0.0198 × BMI (kg/m²))