A method for determining a condition in a blood sample includes: providing a sample of blood; providing a metering probe having a pump for aspirating and dispensing; inserting the metering probe a selected distance into the blood sample; measuring the pressure between the sample and pump during sample aspiration or sample dispense; comparing the measured pressure with a reference value; and signaling the presence or absence of the condition. A method for confirming or detecting the presence of a selected layer of blood component in a centrifuged blood sample includes: measuring a pressure of a suspected selected layer in a metering probe during aspiration or dispense; comparing the measured pressure with a reference value, wherein if the measured pressure and the reference value are substantially identical then the selected layer of the blood component is confirmed. In a preferred embodiment the reference value is a pre-selected pressure range.