Another alternative would be to keep the power supply you have now. And then study and find out what elevated temperature of the blood sample and holder mechanism will work the best. Then afix the regulators to the testing site to act as a heater to warm up the fixturing and the sample to the optimum temperature. The microcontroller can also have a software algorithm that drives an output pin with a PWM signal to a power transistor. This power transistor can switch on and off a 2 -> 10 ohm resistor (selected as appropriate) that is loaded on one of the regulators to adjust the power dissapation in the regulator and thus regulate the temperature. Stable readings may then be possible.

Michael Karas