TABLE 2.
Geometric mean percentage difference in analyte concentration and relation to quality specifications between whole-blood samples processed within 2 hours or after 24 hours1
| Geometric mean percent difference (95% CI) from 2-hour processing | |||
|---|---|---|---|
| Sample type | |||
| Analyte | EDTA | LH | Serum |
| Clinical markers | |||
| C-reactive protein | 3 (−11 to 20) | 0.5 (−13 to 16) | −3 (−16 to 11) |
| Ferritin | 2 (−0.3 to 4) | 1 (−1 to 3) | 0.3 (−2 to 2) |
| Creatinine | 1 (−2 to 4) | 0 (−3 to 3) | 0.7 (−2 to 3) |
| Triglycerides | −2 (−8 to 5) | 2 (−4 to 9) | 0.1 (−6 to 6) |
| HDL cholesterol | −0.1 (−2 to 2) | −2 (−4 to −1)2 | −1 (−2 to 1) |
| Total cholesterol | −0.1 (−2 to 2) | −1 (−2 to 1) | 0.4 (−1 to 2) |
| Fat-soluble vitamins | |||
| 25-hydroxyvitamin D | 2 (3–7) | −1 (−6 to 3) | −4 (−8 to 0.2) |
| Retinol | −0.4 (−7 to 7) | −0.2 (−7 to 7) | 2 (−4 to 9) |
| α-tocopherol | 1 (−4, 6) | −1 (−6, 4) | 1 (−4, 5) |
| γ-tocopherol | 2 (−3 to 7) | −0.6 (−5 to 4) | 2 (−3 to 7) |
| Lutein | 1 (−5 to 8) | −1 (−7 to 5) | 2 (−4 to 9) |
| β-cryptoxanthin | 1 (−4 to 7) | −4 (−9 to 1) | −1 (−6 to 5) |
| Lycopene | 3 (−3 to 9) | −3 (−8 to 2) | −2 (−7 to 4) |
| α-carotene | 2 (−4 to 9) | −6 (−11 to 1) | −5 (−11 to 1) |
| β -carotene | 4 (2–9) | −3 (−8 to 2) | −2 (−7 to 3) |
| Minerals | |||
| Selenium | −1 (−3 to 2) | −1 (−3 to 1) | −1 (−3 to 1) |
| Zinc | 1 (−2 to 3) | 6 (3–8)2, 5 | 1 (−1 to 4) |
| Water-soluble vitamins | |||
| ETKAC (thiamin) | −1 (−3 to 1)3 | −0.3 (−2 to 2) | n/m |
| EGRAC (riboflavin) | 0 (−2 to 2) | −1 (−3 to 0.6) | n/m |
| PLP (vitamin B-6) | 4 (−2 to 10) | −8 (−13 to −2)2, 3 | −14 (−18 to −9)2, 4 |
| PA (vitamin B-6) | 1 (−5 to 7) | 3 (−2 to 9) | −5 (−10 to 0.5) |
| Total folate | −2 (−5 to 1) | −2 (−5 to 1) | 1 (−2 to 4) |
| Vitamin B-12 | −3 (−6 to −0.4)2 | 0.2 (−3 to 3) | −2 (−4 to 1) |
| Holotranscobalamin | 9 (2–16)2, 3 | 5 (−1 to 12) | −4 (−9 to 2) |
| Vitamin C | −43 (−49 to −36)2, 5 | 2 (−9 to 14) | 0.1 (−11 to 12) |
The 24-hour processed samples were mailed, cooled, overnight after collection, and processed on arrival at the laboratory. All analytes were measured in plasma or serum except for ETKAC and EGRAC (measured in saline-washed red blood cells). Percent differences were calculated from a linear mixed model with the random effect of participant ID and fixed effects of treatment and sample type. Quality specifications for bias were calculated from intra- and interindividual variations (22). No superscript indicates better than optimum performance. Abbreviations: EGRAC, erythrocyte glutathione reductase activation coefficient; ETKAC; erythrocyte transketolase activation coefficient; LH, lithium heparin plasma; n/m; not measured, sample type not suitable for analysis; PA, 4-pyridoxic acid; PLP, pyridoxal-5-phosphate.
Significant concentration difference (P < 0.05) from samples that underwent processing within 2 hours of collection.
Percent difference between treatments is between optimal and desirable performance specifications.
Percent difference between treatments is between desirable and minimum performance specifications.
Percent difference between treatments is worse than minimum performance specification.