A method of assaying nucleotide receptor P2X7 pore activity in white blood cells contained within a mixed cell sample is provided comprising labeling white blood cells with a white blood cell-specific label; depolarizing the labeled white blood cells with an isotonic depolarizing solution; contacting the labeled white blood cells with dye and a P2X7 agonist in an amount sufficient to activate P2X7 pore activity; contacting the labeled white blood cells with a divalent cation in an amount sufficient to deactivate P2X7 pore activity; and analyzing dye uptake whereby P2X7 pore activity is quantified by the amount of dye taken up in labeled white blood cells treated with the P2X7 agonist relative to labeled white blood cells in the absence of said P2X7 agonist, said P2X7 pore activity being corrected for sample age and by subtraction of P2X7 pore activity contributed by nonviable white blood cells.