GB2293986A

GB2293986A - Blood sample container

Info

Publication number: GB2293986A
Application number: GB9520787A
Authority: GB
Inventors: Andrew Gunn; Ian David Cameron; David Mcivor Mowat
Original assignee: Iatros Ltd
Current assignee: Iatros Ltd
Priority date: 1994-10-13
Filing date: 1995-10-13
Publication date: 1996-04-17
Anticipated expiration: 2015-10-13
Also published as: GB9420641D0; GB9520787D0; GB2293986B

Abstract

A sample container (1) for use in separating blood into a cellular fraction (7) and a blood plasma fraction (8) comprises an evacuated tube having walls which are substantially transparent to ultraviolet (UV) radiation, a sealable entry port (2) for allowing blood to be transferred into the tube (1), and a gel layer (5). A method is also provided for preparing blood for testing in such a sample container, the method including centrifuging the container (1) to separate the blood plasma and cellular fractions and exposing the sample container to ultraviolet radiation so as to sterilise at least the blood plasma fraction (8). <IMAGE>

Description

BLOOD SAMPLE ANALYSIS The present invention relates to blood sample analysis and in particular to a blood sample container and to a method of rendering safer the use of such a container.

In order to conduct tests on small samples of blood extracted from human patients it is known to make use of a glass or plastic test tube which has its opening sealed by a self-recloseable rubber membrane. The test tube is initially evacuated such that on connection of a transfer tubing between a patient and the test tube a desired volume of blood may be drawn from the patient into the tube. By providing a porous gel layer, usually a silicone polymer, in the test tube it is possible to separate the cellular fraction from the plasma (in order to allow separate analysis of the blood plasma) by spinning the test tube in a centrifuge so that the cellular fraction, which is more dense than the gel layer, passes through the gel to settle at the bottom of the tube with the relatively less dense blood plasma remaining above the gel.

Whilst the transfer of blood from a patient to this type of test tube does not involve serious risk to doctors, nurses or appropriately trained technicians and medical staff, subsequent analysis of the blood plasma and or the cellular fraction may involve some exposure which can lead to the infection of staff with harmful agents, for example bacteria and especially viruses.

It is an object of the present invention to avoid or minimize one or more of the above problems or disadvantages of the prior art and to provide a method and apparatus which enables the analysis of blood samples, and in particular blood plasma, in a manner which substantially eliminates the risk of staff handling the samples being infected by harmful agents within the blood sample. It is also an object of the present invention to enable blood fractions to be sterilised prior to exposure to human handlers.

A further object of the present inventions is to avoid contamination of sophisticated and expensive laboratory equipment which it may be difficult or even impossible to decontaminate.

According to a first aspect of the present invention there is provided a sample container for use in separating blood into a cellular fraction and a blood plasma fraction, the sample container comprising: an evacuated tube having walls which are substantially transparent to ultraviolet radiation and a sealable entry port for allowing blood to be transferred into the tube; and a gel layer which is porous to the cellular fraction and has a density less than the density of the cellular fraction but greater than the density of blood plasma.

Given the relatively high transmissibility of blood plasma to ultraviolet radiation in comparison to that of whole blood or the cellular fraction it is possible quickly to sterilise a blood plasma fraction following the separation procedure.

Whilst this sterilisation procedure may not completely sterilise the cellular fraction this is not essential insofar as only the plasma fraction is required to be accessed for sample testing for most clinical purposes. The provision of the gel layer between the plasma fraction and the cellular fraction prevents recontamination of the sterilised plasma fraction following sterilisation thereof. The sample container preferably comprises a test tube of a suitably W transparent material, for example silica glass or plastics such as low density polyethylene (LDPE) or fluorinated ethylenepropylene copolymer (FEP). Plastics materials are preferred as these can be easily destroyed by incineration. Preferably the transparent material is substantially transparent over at least a part of the range 100 to 400nm.

The seal may be provided by a rubber, or rubber like, insert having a membrane portion which can be penetrated by a hypodermic needle and which reseals itself after withdrawal of the needle. Advantageously, the seal is of a substantially Wtransparent material, e.g. silicone rubber.

According to a second aspect of the present invention there is provided a method of preparing blood for testing, the method comprising the steps of introducing into a sample container as set out in the above first aspect a body of blood, centrifuging the container to separate the blood sample into a blood plasma fraction above the gel layer and a cellular fraction below the gel layer, and exposing the sample container to ultraviolet radiation so as to sterilise at least the blood plasma fraction.

Preferably, the step of exposing the sample container to W radiation comprises exposing the sample for at least two minutes.

The step of sterilising the blood plasma fraction may comprise rotating the sample container about a centrally extending axis in proximity to an ultraviolet light source such that at least a fraction of the blood plasma adjacent the walls of the tube is sterilised as it passes past the ultraviolet light source, the sterilised fraction being subsequently mixed with the main body of the blood plasma fraction.

The method may further include the step of introducing into the blood sample in the container one or more photoactivatable substances for binding to micro-organisms in the blood sample so as to enhance sensitivity of said microorganisms to UV radiation, which substances may conveniently be introduced to the blood sample prior to centrifuging of the container. Alternatively, the one or more photoactivatable substances may be introduced into the blood plasma fraction after centrifugation and prior to exposing the container to UV radiation, this having the advantage of much more rapid sterilisation due to the greater penetration of UV radiation through plasma i.e. after the cellular fraction has been separated out therefrom.Said one or more photoactivatable substances may include a photoactivatable drug such as a psoralen, which is converted from a non-activating form into a micro-organism inactivating form by W radiation.

For a better understanding of the present invention and in order to show how the same may be carried into effect reference will now be made, by way of example, to the accompanying drawings in which: Figure 1 shows a blood sample container at various steps in a blood analysis procedure; and Figure 2 shows a UV sterilisation unit for use with the container of Figure 1; and Figure 3 shows apparatus for sterilising multiple sample containers of the type shown in Figure 1 with a high throughput rate.

There is shown in Figure 1A a blood sample container comprising a conventionally shaped test tube 1 having an upper opening. The upper opening receives an end closure 2 which sealably engages the surrounding inner walls 3 of the test tube 1. The end closure 2 is formed of rubber, or a similar resilient material such as synthetic rubber (which advantageously is substantially W-transparent) and has an inner membrane portion 4 of reduced thickness. The membrane portion 4 is formed and arranged so that it can be penetrated by a conventional hypodermic needle such that on removal of the needle the membrane recloses the hole formed by the needle.

The sample container is provided with a gel layer 5 which initially resides at the bottom of the test tube. The gel layer is of a material which is porous to the cellular blood fraction and has a density which is less than that of the cellular fraction but greater than that of blood plasma. During the fabrication of the sample container the inside of the container may be evacuated and sterilised, for example by exposure to ultraviolet radiation, x-ray or gamma, if necessary.

In order to transfer blood from a human patient into the sample container a length of sterilised tubing is intravenously connected at one end to the patient and at the other end, via a hypodermic needle penetrating the membrane portion 4 of the end closure 2, to the inside of the container (as an alternative to a length of tubing, a double ended needle may be used with a first end of the needle penetrating into a patients vein and the other end penetrating the membrane portion of the container) . The presence of a vacuum within the container causes a given volume of blood 6 to be drawn along the tubing from the patient into the container (Figure 1B).

Once the appropriate volume of blood has been received by the container the hypodermic needle is removed from the membrane 4 which subsequently reseals itself.

The sample container is then placed in a centrifuge and spun at a high rate such that the cellular fraction 7 of the blood sample 6 passes through the gel layer 5 and settles at the bottom of the holder, leaving the blood plasma fraction 8 lying above the gel layer 5 (Figure 1C).

Following separation of the blood into the blood plasma and the cellular fractions, the sample holder is placed in a sterilisation apparatus such as that shown in Figure 2 (which shows a section through the apparatus and sample container at right angles to the longitudinal axis of the container). This apparatus comprises a pair of cylindrical support rollers 9 which contact the outside surface of the sample container and cause the holder to be rotated in an anticlockwise direction.

Four ultraviolet light sources 10 are arranged around the periphery of the sample container and cause ultraviolet radiation to pass through the ultraviolet transparent walls of the sample container into the interior region.

Any U.V. radiation known to be effective in inactivating microorganisms may be used in the apparatus and method of the invention. Suitable U.V. radiation sources include those producing radiation in the wavelength range from 100 to 400nm preferably from 200 to 350nm, for example UVA at approximately 320 to 400nm, UVB at approximately 310nm and UVC at approximately 254nm.

Particular lamp sources which may be mentioned include those available from: GTE Sylvania LTD. of Charlestown, Shipley, West Yorkshire; Thorn EMI of Enfield, Middlesex; and Philips Lighting of Croydon, Surrey, all in England.

The duration of irradiation required will depend on various factors such as the intensity, disposition, and number of sources used, the transmission characteristics of the container side wall material, the container configuration and hence the mixing efficiency therein, the surface area of the thin layer of fluid adjacent the container side wall, and the volume and nature of the fluid being treated. The required duration may however be readily determined by simple trial and error using suitable techniques known in the art for assessing inactivation of the relevant microorganisms and further details are provided hereinbelow. In general the duration will conveniently be in the range from 1 to 60 minutes, preferably from 1 to 30 minutes, e.g. 5 minutes, and the radiation sources are chosen and arranged, to provide an effective inactivating dosage of U.V. radiation within such a period.

Apparatus of the general type shown in Figure 2 is known and is described for example in International Patent Publication WO 89/09067.

The blood plasma fraction 8 is transparent to ultraviolet radiation to an extent which is significantly greater than that of the cellular fraction or of the unseparated blood. It is thus possible to sterilise the blood plasma fraction very quickly in comparison to the time taken to sterilise a whole blood sample or the cellular fraction. For a sample holder having a diameter of approximately 1 cm it is possible to sterilise the blood plasma fraction in a time of 1 to 2 minutes as compared to a time of 15 minutes or more for sterilising a corresponding whole blood sample. In general, it is often only necessary to carry out tests on the blood plasma fraction and therefore the sterilisation of the entire, unseparated, fraction or of the cellular fraction is unnecessary.

Sterilisation will to some degree cause a deterioration in the sample to be tested although this need not be excessive provided that the UV exposure time is kept relatively short.

To compensate for any deterioration which does occur it is possible to create 'nomograms' by experiment to enable the accurate extrapolation of measurements.

Figure 3 shows a schematic drawing of apparatus for sterilising a multiplicity of sample containers at a high throughput rate. The apparatus comprises a pair of parallel rollers 11,12 provided with aligned screw threads 13,14 which act to carry sample containers sequentially from one end of the apparatus to the other, rotating the containers as they travel.

Several containers may be in transit at any one time.

Ultraviolet light sources (not shown) are arranged above the rollers so that the containers are exposed to UV light throughout the transit period.

In order to improve the sterilisation effect produced by the W irradiation, a psoralen, such as 8-methoxy psoralen, may be injected through the membrane portion 4 of the end closure 2 into the blood plasma fraction after centrifuging the sample container 1. Upon exposure to WA radiation of 320 to 400mm wavelength, the 8 methoxy psoralen becomes capable of forming photoadducts with DNA in lymphocytes which may be present in the sample, thereby inactivating these.

It will be apparent that various modifications may be made to the above described embodiment without departing from the scope of the present invention.

Claims

1. A sample container for use in separating blood into a cellular fraction and a blood plasma fraction, the sample container comprising an evacuated tube having walls which are substantially transparent to ultraviolet (UV) radiation and a sealable entry port for allowing blood to be transferred into the tube, and a gel layer which is porous to the cellular fraction and has a density less than the density of the cellular fraction but greater than the density of the blood plasma.

2. A sample container according to claim 1, wherein the container comprises a test tube made of a substantially UVtransparent material.

3. A sample container according to claim 1 or claim 2 wherein the container comprises a test tube made of silica glass.

4. A sample container according to claim 1 or claim 2 wherein the container comprises a test tube made of low density polyethylene (LDPE).

5. A sample container according to claim 1 or claim 2 wherein the container comprises a test tube made of fluorinated ethylene - propylene copolymer (FEP).

6. A sample container according to claim 2, wherein the substantially W-transparent material is substantially transparent to radiation over at least a part of the range 100 to 400 nanometers wavelength.

7. A sample container according to any preceding claim, wherein the sealable entry port is provided by a rubber or rubber like insert having a membrane portion which can be penetrated by a hypodermic needle and which reseals itself after withdrawal of the needle.

8. A sample container according to claim 7, wherein the insert is made of a substantially W-transparent material.

9. A sample container according to claim 7 or claim 8, wherein the insert is made of silicone rubber.

10. A method of preparing blood for testing, the method comprising the steps of: (a) introducing into a sample container according to claim 1 a body of blood; (b) centrifuging the container to separate the blood sample into a blood plasma fraction above the gel layer and a cellular fraction below the gel layer, and (c) exposing the sample container to ultraviolet (W) radiation so as to sterilise at least the blood plasma fraction.

11. A method according to claim 10, wherein the sample container is exposed to W radiation for at least two minutes.

12. A method according to claim 10 or claim 11, wherein the step of sterilising the blood plasma fraction comprises rotating the sample container about a centrally extending axis in proximity to an ultraviolet light sorce such that at least a fraction of the blood plasma adjacent the walls of the tube is sterilised as it passes past the ultraviolet light sorce, the sterilised fraction being subsequently mixed with the main body of the blood plasma fraction.

13. A method according to any of claims 10, 11 and 12, further comprising the step of introducing into the blood sample in the container, one or more photoactivatable substances for binding to micro-organisms in the blood sample so as to enhance sensitivity of said micro-organisms to W radiation.

14. A method according to claim 13, wherein the further step of introducing said one or more photoactivatable substances into the blood sample is carried out prior to the step of centrifuging the container.

15. A method according to claim 13, wherein said one or more photoactivatable substances are introduced into the blood plasma fraction above the gel layer after centrifuging and prior to exposing the sample container to W radiation.

16. A method according to any of claims 13, 14 and 15, wherein said one or more photoactivatable substances include a psoralen.