Lactate Dehydrogenase Activity as Measured by the SMAC Is Related to Flow-Cell Energy

Determination of lactate dehydrogenase (LDH) activity in the SMAC (Technicon) is based on the change in NADH absorbance between two flow cells. We noted that results for patients ’ specimens and controls changed when the fiber optic terminations for the two LDH channel flow cells were adjusted or “peaked ” at the colorimeter chopper assembly. The energy (intensity) of light reaching the flow cells was varied by adjusting the fiber optic terminations, and the absorbance readings for a series of solutions containing NADH and patients ’ specimens were recorded. For both flow cells, when the fiber optic terminations were adjusted to increase the zero absorbance light intensity from 20 lines to 60 lines, a significant (p <0.0001) pro-portional change was seen in the absorbance readings. Evidently the difference in absorbance between the tw