Postpartum determination of umbilical artery blood gases: effect of time and temperature.

complete within 10 min, much shorter than the 90 min for the kinetic cadmium reduction method [13], 45 min for the enzymatic one-step assay [10], and 20 min for the enzymatic method of Moshage et al. [9]. Green et al. [12], by using a high-pressure reduction column coupled with a continuous-flow analyzer, reported a shorter reduction time (within 1 min), and an analysis rate of 30 samples per hour. Although our reduction time is longer, the analysis rate, considering the overall time spent on deproteinization, reduction, and measurement in a Hitachi 717 analyzer, amounts to .150 samples per hour. Recently, Yang et al. [11] described a very sensitive method for chemiluminescent detection of nitrate, but estimates for the analysis rate were 15–30 samples per hour. Moreover, the automated device by Green et al. [12] was specifically designed for analyzing nitrate concentrations and is not available to the majority of clinical chemistry laboratories. By contrast, Hitachi analyzers are widely used and allow simultaneous performance of other analyses. An additional advantage of this method is its low cost, because the cadmium may be regenerated and the reagents are cheaper than those used in enzymatic methods (nitrate reductase or b-NADPH). The semiautomated method described here responds in a quantitative linear fashion to nitrate within the range of 0.8 to 600 mmol/L, whereas the other methods are linear only up to 200–300 mmol/L. The detection limits and the within-run and between-day imprecisions for this method are similar to those reported in the other methods [9, 10, 12, 13]. Values reported for serum are similar to those documented by Moshage et al. [9]. We conclude that this semiautomated procedure provides an easy, less time-consuming, inexpensive, and reliable method of analysis for nitrate concentration in biological fluids, and is therefore suitable for routine performance in clinical chemistry laboratories.