WO2000049401A1

WO2000049401A1 - Apparatus and method for performing hematocrit blood testing

Info

Publication number: WO2000049401A1
Application number: PCT/US2000/004256
Authority: WO
Inventors: Dean L. Kamen
Original assignee: Deka Products Limited Partnership
Priority date: 1999-02-19
Filing date: 2000-02-18
Publication date: 2000-08-24

Abstract

An apparatus and method (200) accurately and reliably measures the hematocrit value in blood or other fluid medium by passing a diluted blood or other fluid through a generally optically transparent measurement flow line (202). The apparatus and method measures the light transmitted (203) through the measurement flow line and the fluid medium and computes a hematocrit value which is compared to a range of optimum values (204). If the measured value does not fall within the range of optimum values, the apparatus and method adjusts the dilution of the blood and other fluid medium with a dilution fluid, such as a saline solution (207), establishing a dilution factor, until the measured hematocrit is within the optimal range. The hematocrit value can then accurately and reliably be computed using the dilution factor (205) and the measured light through the diluted fluid medium.

Description

APPARATUS AND METHOD FOR PERFORMING HEMATOCRIT BLOOD TESTING

RELATED APPLICATIONS

This application is related to and claims the benefit of Provisional U.S. Patent Application Number 60/120,674 entitled APPARATUS AND METHOD FOR MEASURING THE HEMATOCRIT IN BLOOD TESTING, filed February 19, 1999 and incorporated herein by reference.

FIELD OF THE INVENTION This invention relates to blood testing and more particularly, to an improved apparatus and method for performing hematocrit testing on blood.

BACKGROUND Hematocrit is a blood test which serves to measure the proportion of red blood cells to total blood volume. Normal hematocrit test result values range between 42% to 50% for men and between 38% to 47% for women. Hematocrit values may reach as high as 70% when, for example, a person donates serum. During serum donation, whole blood is removed from the donor and is separated, usually by a centrifuge, into a serum component and a red blood cell component. The red blood cell component is then returned to the donor. The returned component may have a hematocrit value as high as 70% during such a procedure.

The use of transmitted light to measure the hematocrit value of blood is well known. One method involves diluting the blood to less than 10% and usually to less than 1%. The blood is then circulated through a flow line across a portion of which has been arranged a light transmitter and a light receiver. The large dilution of the blood allows the measuring device coupled to the light receiver to count each red blood cell as it passes through a transparent portion of the flow line by measuring the "shadow" of each cell as it flows through the flow line. The large dilution factor is required to reduce the occurrence of situations where a second blood cell partially occludes the first blood cell and is therefore miscounted. A disadvantage of this method is that the output is a number count that must be converted to a volume using an assumption regarding the size of the red blood cell. Since the size of red blood cells can vary with certain illness or conditions, the assumption of the size of the red blood cell can lead to errors in the computation of the hematocrit level or value. Such a system and method is well known in the art.

A second measurement method uses the absorption of transmitted light through the flow line. The assumption in such a system is that a reduction of transmitted light is proportional to the volume fraction of the light absorbing material (red blood cells) in the flow line. The advantage of this method is that the volume measurement is directly related to the fraction of light transmitted and undiluted blood samples may be used. U.S. Patent No. 4,303,336 to Cullis, which is fully incorporated herein by reference, discloses a method and apparatus using the second method above wherein undiluted blood is passed though a flow line having a portion of the flow line that is transparent to light. A laser light source is provided that directs the laser beam through the transparent portion of the flow line. The frequency of the laser light is selected to be near a light absorption band of the red blood cells and not near an absorption band of the carrier fluid. The transmitted light is measured by a sensor and the hematocrit level of the blood is calculated. Cullis discloses that hematocrit between 30% to 70% are measurable with his embodiment of the invention. At high hematocrit levels, however, it has been found that the transmitted light readings become less reliable.

Accordingly, what is needed is an apparatus and method of performing hematocrit blood testing which can accurately measure the hematocrit level in a blood sample regardless of the percentage hematocrit level in the sample and the size of red blood cells.

SUMMARY OF THE INVENTION

The present invention provides an improved hematocrit blood testing apparatus and method which overcomes the deficiencies found in prior art systems and methods. In one embodiment of the invention, the apparatus includes a light source and a light sensor capable of measuring light transmitted by the light source. The light source and light sensor are disposed on opposite sides of a measurement flow line, which is generally transparent to light emitted by the light source. The flow line is adapted to allow a sample to flow therethrough. The light sensor provides an output signal which is proportional to the amount or intensity of light flowing through the sample and striking the sensor.

A regulated sample source is in fluid communication with the measurement flow line. The sample source provides a regulated flow rate of a sample to the measurement flow line from a sample supply for analysis of hematocrit level by the disclosed apparatus. In the preferred embodiment, the regulated sample source includes a blood sample flow line, which is in fluid communication with a blood sample pump, which provide the regulated blood sample flow to the measurement flow line.

Also in fluid communication with the measurement flow line is a regulated dilution fluid source. The regulated dilution fluid source provides a suitable dilution medium, such as a saline solution, at a regulated flow rate to the measurement flow line from a dilution medium supply for analysis by the disclosed apparatus. In the preferred embodiment, like the regulated blood sample source, the regulated dilution fluid source includes a dilution fluid flow line, which is in fluid communication with a dilution fluid pump, which provides the regulated dilution fluid flow to the measurement flow line. The flow rate of the dilution fluid and the sample establishes a dilution factor.

The apparatus also includes a processor, responsive to the output signal from the light sensor and to the dilution factor, for controlling the light source and for regulating the sample flow rate and dilution fluid flow rates and for measuring the hematocrit value in a diluted blood sample or other base fluid. Utilizing the above-described apparatus, the disclosed invention provides a method for measuring the hematocrit level in a sample, such as blood, which begins by establishing a sensor baseline by establishing a flow of a dilution fluid through the measurement flow line and measuring the transmitted light through the measurement flow line. Next, the flow of the dilution fluid is secured and a flow of a sample through the measurement flow line is established. Transmitted light through the measurement flow line is then measured while the sample is flowing through the measurement flow line. A flow of the dilution fluid is re-introduced and is adjusted until the light transmitted through the measurement flow line falls within a preset range of values stored in the processor. Based on the sample and dilution fluid flow rates, a dilution factor is calculated. Finally, the hematocrit value is calculated based on the transmitted light through the measurement flow line and the and dilution flow rates provided by the dilution factor.

BRIEF DESCRIPTION OF THE DRAWINGS

These, and other features and advantages of the present invention will be better understood by reading the following detailed description, taken together with the drawings wherein: FIG. 1 is a schematic of one embodiment of the apparatus present invention; and

FIG. 2 is a block flowchart of one embodiment of the method of the present invention.

DETAILED DESCRIPTION OF THE INVENTION One embodiment of a hematocrit measuring apparatus 10, Fig. 1, according to the present invention provides for a diluted blood sample 104 which is flowed though a measurement flow line 100, where light 106 from light source 101, such as a laser type light source, is transmitted through the blood sample flowing through a light transparent portion 108 of measurement flow line 100. Although there are many possible light source types, a light source cannot have a frequency in the absorptive band of the carrier fluid.

The transmitted light 112, which passes through the diluted blood sample 104, is detected by a sensor 102. The sensor 102 produces an output signal 114 whose value is determined by the amount of transmitted light 112 that is detected. The output signal 114 is transmitted to a processor 103. The diluted blood sample 104 is a mixture of blood supplied through a blood flow line 110 from a source of blood or other fluid 118 and a dilution fluid, preferably a saline solution, supplied through a saline flow line 120 from a source of saline or other dilution solution 122. In the embodiment of Figure 1, the blood flow rate m _b. (expressed in milliliters per second) , is maintained and controlled by a blood pump 115 which is in fluid communication with the blood flow line 110. Likewise, in the embodiment of Figure 1, the saline flow rate m_s (also expressed in milliliters per second) is maintained and controlled by a saline pump 125 which is in fluid communication with the saline flow line 120.

Those skilled in the art will appreciate that alternative embodiments of the invention may include alternative systems for regulating the blood and dilution fluid flow rates, such as mixing valves and the like. Such alternatives to the blood and saline pumps are well within the spirit and scope of the present invention.

The processor 103 regulates the blood flow rate _b and the dilution fluid flow rate m _s by controlling the operation of the blood pump 115 and the saline pump 125 through control signal paths 116, 126, respectively. The blood pump 115 and saline pump 116 may be membrane pumps as described in U.S. Patent Nos. 4,976,162 and 5,088,515 which are fully incorporated herein by reference.

In another embodiment of the invention, a mixing chamber 109 may be provided in the measurement flow line 100 where the blood flow line 110 and the saline flow line 120 are merged to form the measurement flow line 100, to provide an area in which the blood or other fluid and the saline solution mix. Further embodiments may include mixing valves, including three-way mixing valves and the like.

As the diluted blood sample 104 flows through the measurement flow line 100, the sensor 102 measures the transmitted light 112 emitted by the light source 101 and which has passed through the diluted blood sample, and sends a signal 114 corresponding to the transmitted light to the processor 103. The processor 103 calculates the hematocrit value of the sample based on the signal 114 transmitted by the sensor 102. The calculation of the hematocrit value from the sensor signal 114 will depend on the characteristics of the sensor and the characteristics of the light source 101 and are known to one of ordinary skill in the art. The processor 103 calculates the hematocrit of the blood by scaling the sample hematocrit by a dilution factor, D, given by the equation, D = (m _b + m_s) /m_b.

In one preferred embodiment of the invention, the bloo d and saline flow rates are adjusted by the processor 103 such that the transmitted light signal 114 produced by the sensor 102 is in an optimum range that is known to provide accurate and reliable measurements of the hematocrit value. The optimum range will depend on several factors such as sensor characteristics, light source characteristics and the geometry of the sensor, flow line, and light source. Optimum range, however, can be easily determined empirically by one of ordinary skill in the art of medical instrumentation and/or medical testing.

One embodiment of the method steps 200, Fig. 2, of the present invention is illustrated wherein a baseline is first established for the apparatus, step 201. To establish the apparatus baseline, the processor 103 establishes a flow of the dilution fluid through the measurement flow line 100. In the embodiment where pumps are used, the dilution fluid flow is established by turning on only the saline pump 125. Accordingly, a pure saline flow through the measurement flow line 100 will be established.

The sensor 102 then measures the light 112 transmitted from the light source 101 through the measurement flow line 100. The processor 103 converts the sensor signal 114 to a value corresponding to 100% light transmission and stores the value as the baseline.

Next, the processor 103 secures the flow of the dilution fluid and establishes a flow of the blood sample through the measurement flow line, step 202. In the embodiment of Fig. 1, this is accomplished by turning off the saline pump 125 and turning on the blood pump 115. As the blood sample flows through the measurement flow line 100, the sensor 102 measures the transmitted light 112 and sends a signal 114 (s _t) to the processor 103, step 203. The processor 103 next compares the signal s _t to a known and preset range of values corresponding to the optimum range for accuracy and reliability to determine if the value is within optimum range, step 204. If the value of s _t is within the preset range of values, the blood hematocrit value is calculated by first calculating the hematocrit value from s _t and the baseline and then scaling the result by the dilution factor given in equation 1, step 205. If in step 204 the processor 103 determines that s _t is outside of the preset range of values, the processor 103 estimates the required saline flow rate to bring s _t into the preset range of values, step 206. The processor 103 then activates and controls the saline pump 125 to produce the estimated saline flow rate, step 207. The loop shown by steps 203, 204, 206, and 207 is repeated until the sensor signal is within the preset range of values.

Accordingly, the present invention provides a novel apparatus and method whereby blood hematocrit testing may be easily, accurately and reliably performed using readily available and reasonably priced technology.

Modifications and substitutions by one of ordinary skill in the art are considered to be within the scope of the present invention which is not to be limited except by the claims which follow.

What is claimed is:

Claims

CLAIMS 1. An apparatus for measuring a hematocrit level of a sample comprising: a light source and a light sensor capable of measuring light transmitted by said light source, said light source and light sensor being disposed on opposite sides of a measurement flow line adapted to allow a sample containing a hematocrit level to flow therethrough, said measurement flow line being generally transparent to light emitted by said light source, whereby said light source, light sensor and measurement flow line form an optical path, said light sensor producing an output signal proportional to an intensity of light transmitted from said light source along said optical path through said sample and striking said light sensor; a regulated sample source in fluid communication with said measurement flow line, for providing a regulated flow of a sample containing a hematocrit level to be measured; a regulated dilution fluid source in fluid communication with said measurement flow line, for providing a regulated flow of a dilution medium to said measurement flow line and for combining with said sample to produce a diluted sample; and a processor, responsive to said output signal from said light sensor and to a dilution factor, for regulating the sample and dilution fluid sources to provide a regulated flow of said diluted sample, and for measuring said hematocrit level of said sample.

2. The apparatus of claim 1, wherein said sample comprises a blood sample.

3. The apparatus of claim 1, wherein said sample source comprises a sample flow line in fluid communication with a sample pump, and wherein said processor regulates said sample source by controlling said sample pump to provide said regulated flow of said sample to said measurement flow line.

4. The apparatus of claim 1, wherein said dilution fluid source comprises a dilution fluid flow line in fluid communication with a dilution fluid pump, and wherein said processor regulates said dilution fluid source by controlling said dilution fluid pump to provide said regulated flow of said dilution fluid to said measurement flow line.

5. The apparatus of claim 1 further comprising a mixing chamber in fluid communication with said regulated sample source and said regulated dilution fluid source, said mixing chamber disposed intermediate said regulated sample and dilution fluid sources and said measurement flow line.

6. The apparatus of claim 1 further comprising a mixing valve in fluid communication with said regulated sample source and said regulated dilution fluid source, said mixing valve disposed intermediate said regulated sample and dilution fluid sources and said measurement flow line.

7. The apparatus of claim 6, wherein said mixing valve comprises a three-way mixing valve.

8. The apparatus of claim 3, wherein said sample pump comprises a membrane pump.

9. The apparatus of claim 4, wherein said dilution fluid pump comprises a membrane pump.

10. The apparatus of claim 1 wherein said dilution factor (D) is calculated according to the equation D = (m _b + m_s ) /m_b .

11. A method of measuring a hematocrit level of a sample, said method comprising the steps of: providing a substantially transparent measurement flow line disposed in an optical path intermediate a light source and a light sensor, wherein light provided by said light source passes through said substantially transparent measurement flow line; establishing a flow of a dilution fluid from a regulated dilution fluid source through said substantially transparent measurement flow line and measuring an amount of light transmitted through said measurement flow line while said dilution fluid is flowing through said measurement flow line; establishing a sensor baseline based on said amount of light transmitted through said measurement flow line while said dilution fluid is flowing through said measurement flow line; generally stopping said flow of said dilution fluid and establishing a flow of said sample from a regulated sample source at a sample flow rate through said measurement flow line; measuring an amount of light transmitted through said measurement flow line while said sample is flowing through said measurement flow line at said sample flow rate; calculating said hematocrit level of said sample based on the transmitted light through the measurement flow line and the blood and saline flow rates provided by a dilution equation; determining if said calculated hematocrit level falls within an optimum range of values; and adjusting a flow rate of said di lution fluid to provide a diluted sample until said calculated hematocrit level falls within said optimum range of values.

12. The method of claim 11 in wherein said step of calculating said hematocrit level further includes calculating a dilution factor of said diluted sample and utilizing said dilution factor to calculate said hematocrit level .

13. The method of claim 11, further comprising the step of adjusting said sample flow rate in conjunction with adjusting said dilution fluid flow rate until said transmitted light falls within a preset range of values.

14. The method of claim 11, wherein said step of establishing a flow of a dilution fluid through said substantially transparent measurement flow line comprises pumping said dilution fluid through said measurement flow line using a dilution fluid pump in fluid communication with a dilution fluid source and said measurement flow line.

15. The method of claim 14, wherein said step of adjusting a flow rate of said dilution fluid comprises controlling said dilution fluid pump.

16. The method of claim 11, wherein said step of establishing a flow of said sample through said measurement flow line comprises pumping said sample through said measurement flow line with a sample pump in fluid communication with a sample source and said measurement flow line.

17. The method of claim 12, wherein said step of adjusting said sample flow rate comprises controlling a pump for pumping said sample from a sample source in fluid communication with said sample pump and said measurement flow line.

18. The method of claim 11, further comprising the step of mixing said sample flow and said dilution fluid flow in a mixing chamber in fluid communication with said regulated sample source, said regulated dilution fluid source and said measurement flow line, said mixing chamber disposed intermediate said regulated sample and dilution fluid sources and said measurement flow line.

19. The method of claim 11 further comprising the step of mixing said sample flow and said dilution fluid flow using a mixing valve in fluid communication with said regulated sample source, said regulated dilution fluid source and said measurement flow line, said mixing valve disposed intermediate said regulated sample and dilution fluid sources and said measurement flow line.