From Lisa Reid-Fifoot, Technical Service Manager at Precision BioLogic:
I am acquainted with an institution that performs several dilutions on the patient’s sample (1/5, 1/10, 1/20, 1/40, 1/80, 1/160) when performing the clottable protein S (PS) assay. They find they are not getting good agreement amongst all the dilutions especially with low results. I have not come across a lab that performs several dilutions for PS patient samples. In my experience the patient sample is usually performed with one dilution for PS.
Hi, Lisa, it is nice to hear from you. There are no documented instances of PS inhibitors, thus the assay is performed on a single dilution. When results are outside the linearity limits, either low or high, the specimen is rediluted and assayed again. Multiple dilutions are likely to produce non-parallel results, as the least dilute and most dilute aliquots are likely to be outside of linearity. Geo.
Is the inconsistency between dilutions the same as might be
Is the inconsistency between dilutions the same as might be seen on a factor assay when an LLI or heparin contamination is present(ie the higher the dilution, the higher the Protein S)? Just a thought.