Abstract: Provided is a detector assembly for determining a ratio of lactate to pyruvate from dialysis, said detector assembly comprising: a first pump, a dialysis probe, a first tube fluidically coupling the first pump to an inlet of the dialysis probe, an infrared (IR) detector, a second tube fluidically coupling an outlet of the dialysis probe to the IR detector, and a controller. The first pump pumps a perfusate at a first flow rate to the dialysis probe, via the first tube, and to, in turn, pump a dialysate at a second flow from the dialysis probe to the IR detector, via the second tube. The IR detector detects respective absorbances due to lactate and pyruvate in the dialysate, and the controller determines the ratio of lactate to pyruvate in the dialysate.