差异代谢物ROC曲线分析
ROC曲线（receiver operating characteristic），亦名受试者工作特征曲线或感受性曲线，是根据一系列不同的二分类方式（分界值或决定阈），以真阳性率（灵敏度）为纵坐标，假阳性率（1-特异度）为横坐标绘制的曲线。代谢组学数据分析获得差异代谢物后，采用ROC曲线来评价并筛选潜在的生物标记物，所使用的分析软件为R(v3.2.1)。
ROC曲线下面积（Area Under Curve，AUC）被用来评估生物标记物对于预测事件发生的灵敏度和特异性，每个代谢物的灵敏度和特异性由ROC曲线的最佳阈值决定[1]。AUC值在0.5~1.0之间，AUC值越接近于1，预测的准确性越高。通常来说，AUC值在 0.5～0.7时预测准确性较低，AUC值在0.7～0.9时有一定预测准确性，AUC值在0.9以上时有较高预测准确性，当AUC值 = 0.5时，该生物标记物对于预测事件发生完全不起作用，无预测价值[2]。
本实验中所得差异代谢物的AUC值见下表：
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| AUC | Ci1 | Ci2 | specificity | sensitivity | threshold | |
|---|---|---|---|---|---|---|
| Creatinine | 1 | 1 | 1 | 1 | 1 | 9862535.30130257 |
| L-2-Hydroxyglutaric acid | 1 | 1 | 1 | 1 | 1 | 3601252.7360659 |
| D-Glucuronic Acid | 1 | 1 | 1 | 1 | 1 | 13047150.0431885 |
| Uridine | 1 | 1 | 1 | 1 | 1 | 22101818.5374028 |
| L-Serine | 1 | 1 | 1 | 1 | 1 | 868297.097627333 |
| Uracil | 1 | 1 | 1 | 1 | 1 | 1579694.67989217 |
| 2,3-Butanediol | 1 | 0.833 | 1 | 1 | 0.833 | 243820833.436089 |
| Azelaic acid | 1 | 1 | 1 | 1 | 1 | 18742113.4255716 |
| Homovanillic acid | 1 | 1 | 1 | 1 | 1 | 22627089.7638657 |
| Epinephrine | 1 | 1 | 1 | 1 | 1 | 19010776.6782833 |
| Gamma-Linolenic acid | 1 | 1 | 1 | 1 | 1 | 2880922.44013587 |
| Tyramine | 1 | 1 | 1 | 1 | 1 | 9146295.88159724 |
| Phenylacetic acid | 1 | 1 | 1 | 1 | 1 | 9597662.83562234 |
| 6-Phosphogluconic acid | 1 | 1 | 1 | 1 | 1 | 11373525.2333363 |
| L-Cysteine | 1 | 1 | 1 | 1 | 1 | 8436309.13989497 |
| Phosphorylcholine | 1 | 0.889 | 1 | 0.833 | 1 | 18675405.0537446 |
| Oleic acid | 1 | 1 | 1 | 1 | 1 | 40674699.6561242 |
| Glycerophosphocholine | 1 | 1 | 1 | 1 | 1 | 2594981.70770881 |
| Limonene-1,2-diol | 1 | 1 | 1 | 1 | 1 | 8759017.4492764 |
| Palmitoyl-L-carnitine | 1 | 0.917 | 1 | 0.833 | 1 | 24511230.8525981 |
| 3-Methyl-2-oxovaleric acid | 1 | 1 | 1 | 1 | 1 | 2670133.50629735 |
| (+)-7-Isojasmonic acid | 1 | 1 | 1 | 1 | 1 | 22785848.8426095 |
| Diacetyl | 1 | 0.846 | 1 | 0.833 | 1 | 34412128.3193931 |
| 1-Pyrroline-2-carboxylic acid | 1 | 1 | 1 | 1 | 1 | 3590732.05104921 |
| 4-Aminobutyraldehyde | 1 | 1 | 1 | 1 | 1 | 8768279.00274905 |
| Dodecanedioic acid | 1 | 1 | 1 | 1 | 1 | 2099884.17916715 |
| Retinol | 1 | 1 | 1 | 1 | 1 | 7715981.13629546 |
| Ethylmethylacetic acid | 1 | 1 | 1 | 1 | 1 | 457982.13502023 |
| Ketoleucine | 1 | 1 | 1 | 1 | 1 | 2751228.85037645 |
| L-Phenylalanine | 1 | 0.833 | 1 | 0.833 | 1 | 5502307.3348656 |
| Cytidine | 1 | 1 | 1 | 1 | 1 | 26281332.6151185 |
| beta-Alanine | 1 | 0.852 | 1 | 0.833 | 1 | 8030403.33713877 |
| Sarcosine | 1 | 1 | 1 | 1 | 1 | 3983498.9987526 |
| (S)-1-Phenylethanol | 1 | 0.944 | 1 | 0.833 | 1 | 893234.275575645 |
| Cortisol | 1 | 1 | 1 | 1 | 1 | 7577138.06458071 |
| dCMP | 1 | 1 | 1 | 1 | 1 | 3471138.36826522 |
| Cinchonidine | 1 | 1 | 1 | 1 | 1 | 119304218.374299 |
| L-Octanoylcarnitine | 0.986 | 0.889 | 1 | 0.833 | 1 | 7308481.56961283 |
| Indole | 0.972 | 0.833 | 1 | 0.833 | 1 | 15760531.3230148 |
| Pelargonic acid | 0.972 | 0.833 | 1 | 0.833 | 1 | 53933889.7193195 |
| Putrescine | 0.972 | 0.889 | 1 | 0.833 | 1 | 4636535.14486855 |
| Capsidiol | 0.972 | 0.704 | 1 | 1 | 0.833 | 5354015.68936652 |
| Decanoyl-L-carnitine | 0.972 | 0.75 | 1 | 0.833 | 1 | 11030571.5687953 |
| Maltol | 0.972 | 0.833 | 1 | 1 | 0.833 | 41105177.8427532 |
| D-Galactose | 0.958 | 0.867 | 1 | 0.833 | 1 | 4059832.24747148 |
| Phthalic acid | 0.944 | 0.692 | 1 | 0.833 | 1 | 8064667.79448882 |
| Phenylacetaldehyde | 0.944 | 0.833 | 1 | 1 | 0.833 | 12837885.6767118 |
| Succinic acid semialdehyde | 0.944 | 0.778 | 1 | 1 | 0.833 | 13940482.1494834 |
| Biotin | 0.944 | 0.778 | 1 | 0.833 | 1 | 22205666.1884894 |
| Dopamine | 0.944 | 0.728 | 1 | 0.833 | 1 | 5508036.37914915 |
| Raffinose | 0.944 | 0.833 | 1 | 0.833 | 1 | 1805.07033129913 |
| Dibutyl phthalate | 0.944 | 0.673 | 1 | 0.833 | 0.833 | 3309736.12777735 |
| 3-Sulfinylpyruvic acid | 0.931 | 0.756 | 1 | 1 | 0.833 | 13578848.1169169 |
| D-Ribose 5-phosphate | 0.931 | 0.735 | 1 | 0.833 | 1 | 7190482.06144378 |
| Se-Methylselenocysteine | 0.917 | 0.75 | 1 | 0.833 | 1 | 29281925.9231605 |
| Dehypoxanthine futalosine | 0.917 | 0.519 | 1 | 1 | 0.833 | 69858860.8736177 |
| 3-Methyl-3-hydroxypentanedioate | 0.917 | 0.667 | 1 | 1 | 0.833 | 10696978.8267016 |
| 2-Heptanone | 0.917 | 0.615 | 1 | 1 | 0.833 | 128139288.25617 |
| (R)-3-Hydroxybutyric acid | 0.917 | 0.75 | 1 | 1 | 0.833 | 2288064.31446293 |
| Erucic acid | 0.917 | 0.667 | 1 | 0.833 | 1 | 3935936.27517863 |
| 6-Aminopenicillanic acid | 0.903 | 0.667 | 1 | 0.833 | 0.833 | 10192013.9009604 |
| O-Phosphoethanolamine | 0.889 | 0.728 | 1 | 0.833 | 1 | 43628867.0007932 |
| 3-Dehydroshikimate | 0.889 | 0.602 | 1 | 0.667 | 1 | 69097435.4739933 |
| Biliverdin | 0.889 | 0.679 | 1 | 1 | 0.833 | 3855356.42088394 |
| Acetoin | 0.889 | 0.722 | 1 | 0.833 | 0.833 | 7020028.26526131 |
| Retinoyl b-glucuronide | 0.889 | 0.596 | 1 | 1 | 0.667 | 20520860.1662013 |
| N-methyl-L-glutamic Acid | 0.889 | 0.679 | 1 | 1 | 0.833 | 9796158.11918899 |
| 17-HYDROXYPROGESTERONE | 0.889 | 0.617 | 1 | 0.667 | 1 | 719196.665105957 |
| (+)-Sesamin | 0.889 | 0.602 | 1 | 1 | 0.833 | 3868133.92699361 |
| Mandelic acid | 0.889 | 0.667 | 1 | 1 | 0.833 | 1805928.04624344 |
| L-Kynurenine | 0.889 | 0.667 | 1 | 0.833 | 1 | 1895670.60567634 |
| Xanthine | 0.889 | 0.679 | 1 | 0.833 | 1 | 2032397.26028509 |
| D-Fructose | 0.875 | 0.574 | 1 | 0.667 | 1 | 6668540.10645784 |
| Dimethylglycine | 0.875 | 0.525 | 0.994 | 0.667 | 1 | 25258103.3114049 |
| N1,N12-Diacetylspermine | 0.875 | 0.59 | 1 | 0.833 | 0.833 | 24923440.4894622 |
| 12-Hydroxydodecanoic acid | 0.861 | 0.667 | 1 | 0.833 | 1 | 3385139.73237699 |
| Dihydrocortisol | 0.861 | 0.568 | 1 | 0.833 | 0.833 | 10119537.2630254 |
| Glyceraldehyde | 0.861 | 0.602 | 1 | 1 | 0.833 | 6544841.15050301 |
| Pipecolic acid | 0.833 | 0.476 | 1 | 0.667 | 1 | 94833924.0635105 |
注：Name，代谢物名称；AUC，ROC曲线下的面积；Ci1，95% CI下限；Ci2，95% CI上限；specificity，特异性值；sensitivity，敏感性值；threshold，鉴别阈值