Interleukin 6 has been an analyte which till recently was rarely used in general clinical practice.
IN these days of COVID 19 it is being widely used to detect IL storm and helps in deciding whether Tocilizumab therapy ought to be given.
It has come to our notice that when tested immediately after collection ( within half and hour) the method of collection or the tube in which it is collected makes not much difference.
But in plain red topped tubes , if it is collected allowed to clot and serum is not immediately separated , the clotting process causes rapid release of Interleukin 6 and results come very high.
The degree of false increase is directly proportional to the amount of time it remains in contact with the clotted cells as varied from 3-4 times to 100 times or more .
Eg 1 . A physician from Valsad who had come in contact with a patient of COVID, but clinically asymptomatic , all inflammatory markers normal , CBC normal, HRCT normal was given an IL6 value of 5500. We collected with precautions and it came 3.
2. In past two days two similar incidents where IL6 of 66o and 1550 when repeated in same day with precautions came 10 and 9 respectively. Just prior to writing this another clinical with IL6 150 was given a result of 10.
We need to run controls to ensure that machines are ok , normally we run three levels of controls to decide that the machine and kit is oK. But here the problem is in collection and processing and transport.
So if your IL6 levels are not correlating clinically please get them rechecked with proper precautions to rule out preanalytical errors, we will be saving some Tocilizumab for actually needy patients.
I have also found that EDTA keeps the level more stable as no clotting happens , and we are already undertaking a study on stability of EDTA plasma which I will let you know in a day or two .
Hope these helps all of you at the frontline !!
Dr Pranav Desai ,
Desai Metropolis laboratory.