Department of Biostatistics, University of Oslo, Oslo, Norway.
BMC Med Res Methodol. 2013 Jan 17;13:6. doi: 10.1186/1471-2288-13-6.
Plasma glucose levels are important measures in medical care and research, and are often obtained from oral glucose tolerance tests (OGTT) with repeated measurements over 2-3 hours. It is common practice to use simple summary measures of OGTT curves. However, different OGTT curves can yield similar summary measures, and information of physiological or clinical interest may be lost. Our mean aim was to extract information inherent in the shape of OGTT glucose curves, compare it with the information from simple summary measures, and explore the clinical usefulness of such information.
OGTTs with five glucose measurements over two hours were recorded for 974 healthy pregnant women in their first trimester. For each woman, the five measurements were transformed into smooth OGTT glucose curves by functional data analysis (FDA), a collection of statistical methods developed specifically to analyse curve data. The essential modes of temporal variation between OGTT glucose curves were extracted by functional principal component analysis. The resultant functional principal component (FPC) scores were compared with commonly used simple summary measures: fasting and two-hour (2-h) values, area under the curve (AUC) and simple shape index (2-h minus 90-min values, or 90-min minus 60-min values). Clinical usefulness of FDA was explored by regression analyses of glucose tolerance later in pregnancy.
Over 99% of the variation between individually fitted curves was expressed in the first three FPCs, interpreted physiologically as "general level" (FPC1), "time to peak" (FPC2) and "oscillations" (FPC3). FPC1 scores correlated strongly with AUC (r=0.999), but less with the other simple summary measures (-0.42≤r≤0.79). FPC2 scores gave shape information not captured by simple summary measures (-0.12≤r≤0.40). FPC2 scores, but not FPC1 nor the simple summary measures, discriminated between women who did and did not develop gestational diabetes later in pregnancy.
FDA of OGTT glucose curves in early pregnancy extracted shape information that was not identified by commonly used simple summary measures. This information discriminated between women with and without gestational diabetes later in pregnancy.
血浆葡萄糖水平是医疗保健和研究中的重要指标，通常通过口服葡萄糖耐量试验（OGTT）进行测量，需要在 2-3 小时内进行多次测量。使用 OGTT 曲线的简单汇总指标是常见的做法。然而，不同的 OGTT 曲线可能产生相似的汇总指标，并且可能会丢失生理或临床相关的信息。我们的主要目的是提取 OGTT 葡萄糖曲线形状固有的信息，将其与简单汇总指标的信息进行比较，并探讨这种信息的临床有用性。
对 974 名处于孕早期的健康孕妇进行了两次两小时内五次葡萄糖测量的 OGTT。对于每位女性，通过功能数据分析（FDA）将五次测量值转换为平滑的 OGTT 葡萄糖曲线，FDA 是专门为分析曲线数据而开发的一组统计方法。通过功能主成分分析提取 OGTT 葡萄糖曲线之间时间变化的基本模式。所得功能主成分（FPC）得分与常用的简单汇总指标进行比较：空腹值和两小时（2-h）值、曲线下面积（AUC）和简单形状指数（2-h 减去 90-min 值，或 90-min 减去 60-min 值）。通过对孕妇后期葡萄糖耐量的回归分析探讨了 FDA 的临床有用性。
超过 99%的个体拟合曲线之间的变化可以用前三个 FPC 来表示，从生理学上解释为“总体水平”（FPC1）、“峰值时间”（FPC2）和“波动”（FPC3）。FPC1 得分与 AUC 高度相关（r=0.999），但与其他简单汇总指标的相关性较弱（-0.42≤r≤0.79）。FPC2 得分提供了简单汇总指标无法捕捉到的形状信息（-0.12≤r≤0.40）。FPC2 得分，而不是 FPC1 或简单汇总指标，可区分孕妇后期是否患有妊娠期糖尿病。
在孕早期，OGTT 葡萄糖曲线的 FDA 提取了常用简单汇总指标无法识别的形状信息。该信息可区分孕妇后期是否患有妊娠期糖尿病。
