Table 1.
Comparison of total folate measured at baseline by HPLC-MS/MS and MBA for various matrices1
| Sample Matrix | Descriptive Statistic | HPLC-MS/MSExcluding MeFox | HPLC-MS/MSIncluding MeFox | MBA |
|---|---|---|---|---|
| Serum2 | Mean±SD, nmol/L | 28.6±12.5 | 32.3±12.7 | 28.8±12.8 |
| Median (IQR), nmol/L | 27.2 (19.2 to 35.2) | 30.44 (23.0 to 37.9) | 28.40 (18.5 to 34.3) | |
| Pearson correlation r | 0.993 | 0.978 | n/a | |
| Relative difference (95% CI)3, % | −0.4 (−1.83 to −1.03) | 15.4 (11.5 to 19.4) | n/a | |
| Weighted Deming regression slope (95% CI) | 0.992 (0.964 to 1.020) | 1.017 (0.950 to 1.083) | n/a | |
| Weighted Deming regression intercept (95% CI) | 0.064 (−0.542 to 0.067) | 3.07(1.247 to 4.898) | n/a | |
| WB-Lysate4 | Mean±SD, nmol/L | 886±255 | 1033±295 | 1089±300 |
| Median (IQR), nmol/L | 893 (724 to 996) | 1028 (855 to 1165) | 1109 (893 to 1205) | |
| Pearson correlation r | 0.963 | 0.970 | n/a | |
| Relative difference (95% CI)3, % | −18.6 (−20.3 to −16.9) | −5.12 (−6.85 to −3.40) | n/a | |
| Weighted Deming regression slope (95% CI) | 0.824 (0.767 to 0.882) | 0.958 (0.899 to 1.017) | n/a | |
| Weighted Deming regression intercept (95% CI) | −12.81(−71.51 to 45.9) | −11.4 (−69.7 to 46.9) | n/a | |
| RBC-Lysate5 | Mean±SD, nmol/L | 899±271 | 1071±319 | 1037±295 |
| Median (IQR), nmol/L | 900 (739 to 1019) | 1051 (852 to 1186) | 1052 (839 to 1180) | |
| Pearson correlation r | 0.971 | 0.975 | n/a | |
| Relative difference (95% CI)3, % | −13.5 (−15.2 to −11.8) | 3.13 (1.36 to 4.89) | n/a | |
| Weighted Deming regression slope (95% CI) | 0.901 (0.845 to 0.958) | 1.066 (1.005 to 1.127) | n/a | |
| Weighted Deming intercept (95% CI) | −36.5 (−91.2 to 18.1) | −35.4(−91.9 to 21.2) | n/a |
Total folate by HPLC-MS/MS is the sum of folate forms (5-methyltetrahydrofolate, 5-formyltetrahydrofolate, tetrahydrofolate, 5,10-methenyltetrahydrofolate, excluding or including MeFox); MBA, microbiologic assay
Serum samples (n=60); aliquots processed and analyzed as duplicates by HPLC-MS/MS and MBA over 2 days (n=4 results per sample)
Calculated as HPLC-MS/MS minus MBA divided by MBA (expressed as percent) and then averaged across all 60 samples
WB-Lysate samples (n=60); conventionally prepared as follows: whole blood aliquot from each sample diluted 1/11 with 1% ascorbic acid, then frozen; prior to analysis by HPLC-MS/MS, WB-Lysate aliquots were incubated for 4 h at 37°C; WB-Lysate aliquots for MBA were not incubated prior to analysis; aliquots processed and analyzed as duplicates by each assay over 2 days (n=4 results per sample).
RBC-Lysate samples (n=60); washed RBC samples diluted approximately ½ with saline prior to 1/11 dilution with 1% ascorbic acid, then frozen; prior to analysis, RBC-Lysate aliquots were treated with exoGGH enzyme (5 μg/mL of lysate) for 30 min at room temperature; aliquots processed and analyzed as duplicates by each assay over 2 days (n=4 results per sample).