Abstract: A method for monitoring a therapeutic treatment regime in an individual having a disease, comprises: providing at a first location a solid substrate capable of immobilising a biomarker characteristic of the disease and a therapeutic compound in the biological sample, contacting the biological sample with the solid substrate to immobilise the biomarker and the therapeutic compound; transferring the solid substrate with the immobilised biomarker and therapeutic compound to a second location; performing an extraction step on the solid substrate to extract the biomarker and the therapeutic compound; performing a first detection assay to detect and/or quantify the biomarker, performing a second detection assay to quantify the therapeutic compound; and correlating the detection and/or quantity of the biomarker with the disease state of the individual, and comparing the quantity of the therapeutic compound with a target level for treatment of the disease, thereby to assess the efficacy of the treatment regime.