Effect of anticoagulants on the chromogenic Limulus lysate assay for endotoxin.

We have examined the effects of anticoagulants on the chromogenic Limulus lysate assay for endotoxin. The results indicate that both heparin and CPD Adenine 1 have a striking dose related inhibitory effect on the assay. At concentrations of heparin as low as about 30 U/ml there was a 90% reduction in detectable endotoxin. The inhibitory effect of up to 100 U/ml of heparin could be neutralised by the addition of protamine sulphate. Anticoagulants appear to be an additional factor which can adversely affect the Limulus chromogenic assay for endotoxin. This further emphasises the need for alternative approaches to the measurement of endotoxin.