Table 4 Summary of studies comparing tracer methods to estimate fractional calcium absorption^a

265 women

554 measures, 5-h serum, GSM: average of oral to iv tracer valuesin multiple serum and urine samples collected for 6-10 days

^cFCA = 2.3045(Serum) + 0.021953(Weight^0.425) (Height^0.725) - 0.1735

R² 0.91

≥35 years old [3]

p not provided

30 men

New method at baseline and GSM 6 days later, 5-h serum, GSM: quotient of 5-h oral radioactivity to 3-h iv radioactivity

^cFCA = (Serum)^0.92373 x (0.385 x (Height^0.5285) (Weight^0.3721))

R² 0.90

20-60 years old [20]

p < 0.001

12 men

24 measures, 5-h serum, GSM: average of oral to iv tracer values in multiple serum and urine samples collected at multiple times, and quotient of 5-h oral radioactivity to 3-h iv radioactivity

Not provided

R² 0.92

36 ± 5 years old [21]

p not provided

19 men and women

19 measures, 4-h serum, GSM: ratio of cumulative recovery of oral to iv tracers in 24-h urine collection

^eFCA = ratio of oral calcium tracer to intravenous tracer

R² 0.83

≥50 years old [10]

p < 0.001

22 girls

31 measures, 4-h serum, GSM: Average of 3 values- oral to iv ratio in 24-h serum, 24-h urine and kinetic model

^c,d,fFCA = 1.334(Serum)^0.7872BSA^1.7132e^{(-0.01652PMA)}

R² 0.94

10-15 years old [8]

p < 0.001

26 women

129 measures, 4, 5, 6 h serum, GSM: Average of 3 values- oral to iv ratio in 24-h serum, 24-h urine and kinetic model

^cFCA = 1.3609(4 h Serum)^0.8703BSA^0.8708

R² 0.78

19-67 years old [9]

p < 0.001

^cFCA = 1.4065(5 h Serum)^0.8437BSA^0.7785

R² 0.78

p < 0.001

^cFCA = 1.5828(6 h Serum)^0.8636BSA^0.7142

R² 0.81

p < 0.001