WO1989004961A1

WO1989004961A1 - Hematology cell counting apparatus

Info

Publication number: WO1989004961A1
Application number: PCT/US1988/004051
Authority: WO
Inventors: Henri Bady
Original assignee: Techne Corporation
Priority date: 1987-11-13
Filing date: 1988-11-14
Publication date: 1989-06-01

Abstract

A hematology cell counting chamber for counting particulate blood components in a sample utilizing an impedance circuit. The unit includes a sample chamber (20), a generally linear passage (21) extending away from the sample chamber, an orifice (30) interposed generally between the sample chamber and the linear passage means, and an electrical circuit including a first electrode (22) disposed in the sample chamber and a second electrode (38) disposed in the linear passage means. The circuit means provides an electrical current within the sample to detect passage of blood particles through the orifice. The linear passageway is of a relatively small diameter to inhibit turbulence in the blood sample after it passes through the orifice, thereby reducing erroneous swirlback counting of such particles.

Description

HEMATOLOGY CELL COUNTING APPARATUS TECHNICAL FIELD

The invention relates to hematology analyzers for counting blood cells, and more particularly to a cell counting chamber system.

BACKGROUND OF THE INVENTION

Blood components including platelets, white blood cells, and red blood cells may be counted by at least two popular methods, the impedance method and laser systems. In the impedance method, liquid containing the particles of interest is diluted using suitable isotonic solutions, including an electrolyte such as sodium chloride or potassium chloride. A probe having a single orifice, typically a ruby with a very precise hole in it, is inserted into a chamber containing the diluted sample. Two electrodes are provided, one within the hollow chamber of the probe, and the other located in the sample. Upon applying voltage to the electrodes, an ionic current is induced in the electrolytic solution, the current of necessity passing through the ruby orifice.

Simultaneously with passage of the current, fluid is either drawn by vacuum or pumped into the probe through the orifice. As cells or cell particles pass through the orifice, they partially block the flow of electrolyte through the orifice, therefore changing the resistance or impedance in the circuit, a change which is detectable with a galvanometer or other suitable circuitry. Based on the amount and duration of change ("pulse volume") in the resistance of the circuit, the type and number of cells passing through the orifice can be determined. White blood cells typically have a volume of about 120-1,000 cubic microns, red blood cells 85-95 cubic microns, and platelets 2-30 cubic microns.

A typical prior art probe is illustrated in Figure 1. An artifact of such probes is that passage of fluid through the ruby orifice creates turbulence within the probe, permitting a discernible percentage of cells to swirl back and again pass through the cell counting zone. Due to the dynamics of the fluid flow and electron flow, a cell passing through the zone a second time typically has a pulse amplitude significantly smaller, therefore causing errors in the cell count which are difficult to compensate for electronically_

It should be noted that when cells swirl back, as is graphically illustrated in Fig. 1, it is not necessary for the cells to actually pass backwards through the orifice for them to be detected. Rather, if they merely pass through the counting zone adjacent the orifice so as to temporarily interrupt or alternate current passage, such recirculation will be misinterpreted by the system, commonly as a particle of smaller size. Thus, for example, a recirculating red blood cell may be erroneously recognized as a platelet.

SUMMARY OF THE INVENTION

The invention relates to a counting chamber which includes an orifice mounted at the end of a hollow internal electrode through which a sample is drawn, as by a vacuum. The particles pass through a small opening before passing through the orifice, and continue in a straight path well beyond the counting zone as they are being evacuated. Turbulence is therefore substantially reduced, and the swirlback effect drops substantially.

In a preferred embodiment, the system is comprised of three parts which are easily disassembled for cleaning. The parts include a sample chamber, the orifice mount, and the electrode, the latter two defining the evacuation passage. The three parts may be assembled to one another by snug fittings sealed with O-rings which are disassembleable from one another by hand.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a schematic cross-sectional view of a prior art probe tip including a counting orifice;

Figure 2 is a schematic view of the counting chamber system of the invention;

Figure 3 is a schematic drawing of the orifice and evacuation path;

Figure 4 is a schematic drawing of the chamber of the invention illustrating the separable parts;

Figure 5 is a cross-sectional view of a preferred embodiment of the invention; and

Figure 6 is a partially broken-away view of the area in which the orifice is mounted.

DETAILED DESCRIPTION OF THE INVENTION

Referring to Fig. 2, a sample which has been diluted to the proper proportion is drawn through input (21) into chamber (20) which includes an electrode (22) . Cells are drawn, as by vacuum, toward and through an orifice (30), preferably a ruby orifice, and then pass through hollow electrode (38), and are aspirated away. Fig. 3 shows in schematic fashion the cell counting zone (35) centered about the orifice, and illustrates the substantially linear path of cells, which path effectively eliminates turbulence which gives rise to swirlback and erroneous counting of blood components.

Figs. 4-6 illustrate in greater detail a preferred embodiment of the invention. The sample chamber (20) includes a cover (25) with a thumb screw (26) securing it in place. An air/bubble input (23) is provided for mixing, and a drain (24) is also provided to allow evacuation of fluids from the sample chamber (20) .

The orifice mounting block (31) is snugly received within a complimentary fitting in the sample chamber block, and secured by pressure between the two pieces against an 0-ring (32) . The orifice mounting block (31) is provided with a rinse input (33) and rinse output (34) .

The electrode mount (38) similarly fits into the other end of the orifice mounting block (31), secured by a similar O-ring (39). Fluid is evacuated through the distal end (40) of the electrode mount.

The three-piece manufacture of the chamber allows convenient disassembly and reassembly of the various pieces for cleaning and maintenance. The device therefore provides for a relatively simple solution to the otherwise complex problem of discriminating swirlback signals from true counting signals.

While a preferred embodiment of the present invention has been described, it should be understood that various changes, adaptations and modifications may be made without departing from the spirit of the invention and the scope of the appended claims.

Claims

WHAT IS CLAIMED IS:

1. A hematology cell counting chamber for counting particulate blood components in a sample utilizing an impedance ciruit, comprising a sample chamber, means defining a generally linear passage extending away from the sample chamber, orifice means interposed generally between the sample chamber and the linear passage means, and electrical circuit means including an electrode disposed in the sample chamber and a second electrode disposed in the linear passage means, the circuit means providing an electrical current within the sample to detect passage of blood particles through the orifice, the linear passageway being of a relatively small diameter to inhibit turbulence in the blood sample after it passes through the orifice, thereby reducing erroneous swirlback counting of such particles.

2. A hematology cell counting chamber system substantially as described and shown.