I have to examine various cytokines as well as liver enzymes from serum, but I have a very small amount, so i want to know whether it can be used after diluting it? if yes then what should be the ratio of dilution?
Yes, I think you can dilute your small volume serum samples (1:1) and then multiply your reading by dilution factor. Any way it is preferred not to make dilutions to get good results.
yes, you can dilute it especially when you have a severe liver damage, leading to increase in the levels of the liver enzymes in the serum. there are certain biological agents that can inhibit the activities of these enzymes in the serum. an example is bilirubin. so when you read the absorbance on a spectrophotometer, you will notice that the readings (kinetics) do not flow as it suppose to be. but you will notice that when you dilute the sample using normal saline, the readings will flow. you can use 1:10 dilution which is specified by most assay kits for liver enzymes, then you multiply the final activity by 10. you may find this useful
You definately can, as for the dilution factor; most commercial ELISA kits that are optimized for serum/plasma give suggestions. Obviously it also depends on the cytokine you want to measure, if you have a rough estimation of the cytokine levels you can expect (e.g. from literature) at least make sure that the final concentration of your sample will fit the standard curve of your ELISA.
It depends on the methods and original concentrations of the studied markers. You might want to use something like "High-sensitivity" kits for ELISA (they are usually more expensive) first and than move to regular ones if concentration of the cytokines is sufficient for dilution.