Is there any reason you particularly want to use LDH to test for cytotoxicity? There are a number of other measures which should be simpler without a kit

Here is a very simple LDH assay protocol. I apologize for the formatting (it's pasted from a word doc)

Extracellular LDH assay: Lactate → Pyruvate

Assay Buffer: 

686 µM                 MW: 505.7           Iodonitrotetrazolium chloride (INT)                       (Sigma#: I8377-1G)

291 µM                 MW: 306.3           Phenazine Methosulfate (PMS)                                                (Sigma#: P9625-1G)

1.35 mM               MW: 663.4           B-Nicotinamide Adenine Dinucleotide (NAD)    (Sigma#: N7004-1G)

200 mM                MW: 121.1           Tris(hydroxymethyl)aminomethane pH 8.2         (Sigma#: 252859-100G)

55.5 mM               MW: 96.0             Lithium L-lactate                                                              (Sigma#: L2250-25G)

Method:

___         Culture and treat cells according to experimental design

___         Remove media, centrifuge at 200 g for 5 min.

___         Transfer 30 µL supernatant to 96 well plate.

___         Add 100 µL/well Assay buffer and take multiple readings, (absorbance at 492 nm w/ background at 690 nm), within 1 hour.

Thank you very much!

Michael Nicholls How do you stop enzymatic reaction ? In kits, you have to add a stop solution after 30 minutes;

Thks !

By changing the pH value. Most kits use acetic acid (1M).