Is a quantification of Interleukin 1 Receptor Antagonist (IL1-RA). Inhibits the activity of interleukin-1 by binding to receptor IL1R1 and preventing its association with the coreceptor IL1RAP for signaling. Has no interleukin-1 like activity. Binds functional interleukin-1 receptor IL1R1 with greater affinity than decoy receptor IL1R2; however, the physiological relevance of the latter association is unsure. The trait is Experimental Factor Ontology identifier EFO_0004754 (interleukin 1 receptor antagonist measurement).