Detection of H-ras mutations in urine sediments by a mutant-enriched PCR technique.

higher MetHb values in the presence of HbF. For MetHb concentrations of 15% or less, i.e., values most likely to be encountered clinically with NO therapy, the Corning 270, in agreement with the study carried out previously (5), was unaffected by the presence of HbF in the umbilical cord sample (P 5 0.7380). By contrast, the Chiron 800 showed a constant error to significantly higher MetHb (P 5 0.0047) for MetHb concentrations of 15% or less. The manual method was unaffected by the presence of HbF in the cord blood samples. These results indicate that, in the presence of HbF, the Chiron 800 CO-oximeter produces falsely increased MetHb values in the clinically significant range. Overestimation of MetHb in the presence of HbF may have serious implications, with the possibility of NO therapy being discontinued prematurely. The proportional bias of the Corning 270 is apparent only at values .15% and hence would seem clinically insignificant. The absorbance peak at 632 nm is the optimal region for measuring MetHb if we consider 100% adult or 100% fetal hemoglobin (HbF). Unfortunately, this 632-nm region also corresponds to a considerable difference between the absorbance spectra of adult hemoglobin and HbF (7). This difference is minimal at 610 nm, an isosbestic point. Below 610 nm, however, the absorbance curves become very steep, indicating that a compromise using wavelengths between 610 and 625 nm, for example, may prove better. According to Chiron Diagnostics, the 10 wavelengths chosen for the 800 series CO-oximeter avoid the region between 580 and 610 nm (8); in contrast, the Corning 270 uses two wavelengths in this region (597 and 605 nm). For neonates receiving NO therapy, we recommend continued use of the model 270 CO-oximeter for monitoring of MetHb.