Disclosed are liquid and solid assay compositions and portable sample reader devices for use in a sample-to-answer diagnostic system for the detection of one or more analytes, preferably the detection of circulating histones in whole blood. Further provided are methods of making and using the assay compositions and portable sample reader, including the collection of a raw sample, testing the sample using the assay compositions, and analyzing the sample via the portable sample reader. More particularly, assay compositions comprising a sacrificial partition, target molecule, detectable label, and sacrificial partition are used in combination with a sample reader comprising an optical system and a housing unit as part of a sample-to-answer diagnostic system for quantifying circulating histones in whole blood as a mechanism of predicting the risk of multiple organ failure.