System and method for aggulutination detection

A method of determining the presence or absence of a target substance in a sample comprising:

• combining the sample with agglutination reagents specific for the target substance to form a reaction mixture;
• flowing the reaction mixture along a path having a predetermined width past a transparent read area;
• illuminating the flowing mixture at the read area;
• detecting in a direction from one side of the path to the other at a plurality of read area locations light received through the flowing mixture;
• generating a series of signals for each of the plurality of read area locations having a value corresponding to the detected illumination;
• calculating variations in the value of the signals at each read area during a predetermined time interval, wherein the step of calculating the variations in the signals comprises the substeps of passing each signal of each detector through a low pass filter equation
• LP.sub.i =K1 Input.sub.i +(1-K1).degree.LP.sub.i -1
• and a high pass filter equation
• HP.sub.i =HP-1+Input.sub.i -LP.sub.i,
• where
• i is the current signal number,
• Input.sub.i is the current input signal,
• K1 is a filter constant between 0 and 1,
• LP.sub.i is the current accumulated Low Pass filtered data, and
• HP.sub.i is the current accumulated High Pass filtered data;
• determining the absence of the target substance in the flowing mixture in response to the calculation of a predetermined number of calculated variations for each of a predetermined plurality of the read area locations;
• and
• determining the presence of the target substance in the flowing mixture in response to calculation of less than the predetermined number of value variations during the predetermined time interval.