Deuterium oxide (D₂O) appearance in blood is a marker of fluid bioavailability. However, whether biomarker robustness (e.g., relative fluid delivery speed) is consistent across analytical methods (e.g., cavity ring-down spectroscopy) remains unclear. Fourteen men ingested fluid (6 ml/kg body mass) containing 0.15 g/kg D₂O followed by 45 min blood sampling. Plasma (D₂O) was detected (n = 8) by the following: isotope-ratio mass spectrometry after vapor equilibration (IRMS-equilibrated water) or distillation (IRMS-plasma) and cavity ring-down spectroscopy. Two models calculated D₂O halftime to peak (t_1/2max): sigmoid curve fit versus asymmetric triangle (TRI). Background (D₂O) differed (p < .001, η² = .98) among IRMS-equilibrated water, IRMS-plasma, and cavity ring-down spectroscopy (152.2 ± 0.8, 147.2 ± 1.5, and 137.7 ± 2.2 ppm), but did not influence (p > .05) D₂O appearance (Δppm), time to peak, or t_1/2max. Stratifying participants based on mean t_1/2max (12 min) into “slow” versus “fast” subgroups resulted in a 5.8 min difference (p < .001, η² = .73). Significant t_1/2max model (p = .01, η² = .44) and Model × Speed Subgroup interaction (p = .005, η² = .50) effects were observed. Bias between TRI and sigmoid curve fit increased with t_1/2max speed: no difference (p = .75) for fast (9.0 min vs. 9.2 min, respectively) but greater t_1/2max (p = .001) with TRI for the slow subgroup (16.1 min vs. 13.7 min). Fluid bioavailability markers are less influenced by which laboratory method is used to measure D₂O as compared with the individual variability effects that influence models for calculating t_1/2max. Thus, TRI model may not be appropriate for individuals with slow fluid delivery speeds.

血液中出现氧化氘 (D ₂ O) 是液体生物利用度的标志。然而，生物标志物的稳健性（例如，相对流体输送速度）在分析方法（例如，腔衰荡光谱）中是否一致仍不清楚。_{十四名男性摄入含有 0.15 g/kg D 2} O的液体（6 ml/kg 体重），然后进行 45 分钟的血液采样。等离子体 (D ₂ O) 通过以下方法检测 ( n  = 8)：蒸汽平衡（IRMS 平衡水）或蒸馏（IRMS 等离子体）和空腔衰荡光谱后的同位素比质谱法。两个模型计算了 D ₂ O 半峰时间 ( t _1/2max)：S 形曲线拟合与不对称三角形 (TRI)。背景 (D ₂ O) 在 IRMS 平衡水、IRMS 等离子体和腔衰荡光谱（152.2 ± 0.8、147.2 ± 1.5 和 137.7 ± 2.2 ppm）之间存在差异（p < .001，η 2 =  .98 ^） , 但不影响 ( p  > .05) D ₂ O 外观 (Δppm)、达峰时间或t _1/2max。根据平均t _1/2max（12 分钟）将参与者分为“慢”和“快”子组，结果相差 5.8 分钟（p  < .001，η ²  = .73）。重要的t _1/2max模型 ( p  = .01, η ² = .44) 和模型 × 速度子组相互作用 ( p  = .005, η ²  = .50) 的影响被观察到。TRI 和 S 形曲线拟合之间的偏差随着t _1/2max速度的增加而增加：对于快速（分别为 9.0 分钟和 9.2 分钟）没有差异 ( p  = .75)，但 对于 TRI更大的t _1/2max ( p = .001)慢子组（16.1 分钟对 13.7 分钟）。与影响计算t _1/2max的模型的个体变异性效应相比，流体生物利用度标记物受使用哪种实验室方法测量 D _{2 O 的影响较小}. 因此，TRI 模型可能不适合输液速度慢的个体。