Table 3.

Performance of spot urine samples taken at different times to predict 24-hour urine excretions (Tufts sample; n = 20 participants)

Variables	Lin's CCC	95% CI	Bias (mg/24 hour)	95% LoA (mg/24 hour)	P30
Oxalate
Morning fasting	0.71	0.50–0.92	−1.7	−24.8–21.5	75.0
Preprandial	0.96	0.92–0.99	1.0	−9.6–11.5	95.0
Postprandial	0.40#	0.09–0.72	−7.5	−37.9–23.0	70.0
Calcium
Morning fasting	0.80	0.66–0.95	−18	−116–79	75.0
Preprandial	0.63	0.39–0.87	−7	−163–150	60.0
Postprandial	0.44	0.11–0.77	−6	−210–158	35.0
Magnesium
Morning fasting	0.87	0.75–0.98	−13	−63–37	60.0
Preprandial	0.84	0.71–0.97	−6	−68–56	65.0
Postprandial	0.78	0.62–0.95	1	−78–80	60.0
Citrate
Morning fasting	0.90	0.81–0.98	−10	−237–217	85.0
Preprandial	0.86	0.74–0.97	27	−281–334	95.0
Postprandial	0.81#	0.66–0.96	−98	−383–187	65.0
Uric acid
Morning fasting	0.67	0.42–0.92	−14	−329–301	75.0
Preprandial	0.74	0.54–0.93	−64	−293–166	85.0
Postprandial	0.78	0.64–0.93	−85	−326–155	70.0

*P < 0.05 versus morning fasting. Prediction 1 was used to estimate 24-hour urinary excretions.