GB2230856A

GB2230856A - Storing urine samples

Info

Publication number: GB2230856A
Application number: GB8908404A
Authority: GB
Inventors: Harry Keen; Gian Carlo Viberti
Original assignee: St Thomas Hospital Medical School
Current assignee: St Thomas Hospital Medical School
Priority date: 1989-04-13
Filing date: 1989-04-13
Publication date: 1990-10-31
Also published as: GB8908404D0

Abstract

Samples are stored contacting urine with an absorbent material, which material incorporates a anti-bacterial agent, and enclosing the absorbent material in a moisture impermeable container. Absorbent is e.g. sponge, pretreated filter paper or polystyrene.

Description

A METHOD OF STORING A URINE SAMPLE The present invention relates to a method of storing a urine sample and to an absorbent material suitable for use in such a method.

In medical diagnosis it is often necessary to assay urine samples to determine the amounts of particular substances, for example proteins, contained therein. For example, in order to make an early diagnosis of diabetic kidney diseas, early morning urine may be assayed to determine the level of human albumin and creatinine concentrations. This will identify diabetics with a raised or rising urinary albumin excretion. The latter can be determined only by estimating multiple (20-50) serial samples. This multiple sampling offers the potential for very early diagnosis of diabetic kidney disease at a time when protein excretion is systematically rising within the normal range and at a time the condition is most readily amenable to control or reversal.To obtain the urine sample in the usual way it is often necessary for the patient or subject to travel daily to hospital to give the urine sample. This is expensive and inconvenient, especially when it is desired to assay many repeated samples of early morning urine. Even if the sample is obtained in a hospital, the sample would need to be processed or frozen until analysis if this was to be done without degradation by bacterial decomposition.

We have discovered a method of collecting and storing a urine sample satisfactorily and stably before it is assayed, such that the patient or subject can easily collect and prepare his or her own sample'and store it in a form which can, if required, conveniently be transmitted to the hospital or diagnosis unit, for example by post. This avoids the problem of the patient or subject having to make frequent trips to the hospital and the expense of professional nursing time involved in looking after the patient or subject at the hospital and also makes feasible the collection of a large number of daily samples over relatively long periods of time.

The present invention provides a method of storing a urine sample which comprises contacting urine with an absorbent material, which material incorporates an anti-bacterial agent, and enclosing the absorbent material in a moisture impermeable container.

The present invention also provides an absorbent material suitable for use in such a method which incorporates an anti-bacterial agent.

In the method of the present invention the urine is stored on an absorbent material. This has two advantages.

Firstly the material can be placed in the stream of urine being passed, which is a more convenient and user-acceptable way of obtaining a small sample than with a sample bottle.

Secondly, the absorbent material can easily be placed in and removed from a moisture impermeable container which can also act as a recipient container for the liquid when it is recovered from the material, for example by centrifugation.

Should the container break, the sample would also not be completely lost.

The absorbent material may be any material which does not adsorb the substances which it is desired to assay.

This is to ensure that the substances which are to be assayed can be recovered from the material. It is therefore possible to use a material which naturally does not adsorb the substance to be assayed. A number of synthetic plastic materials such which can be spun into an absorbent form such a fabric can be used, for example polystyrene, as they do not adsorb, for example, proteins. A natural or synthetic sponge may be used. Untreated filter paper adsorbs some substances suc as human albumin although it does not adsorb the non-protein substance creatinine. Therefore to assay proteins such as human albumin it must be treated to prevent adsorption of the urinary proteins. The absorbent material may be so treated by contacting it with an agent which blocks protein binding sites such that it no ionger adsorbs the urinary proteins.This can be done, for example, by contacting the material with a protein other than that which is to be assayed, for example a solution of bovine serum albumin or gelatin. The solution is preferably an aqueous solution. If bovine serum albumin is used, the concentration thereof in the solution should be at least 0.025 percent by weight. All the binding sites on the filter paper must be blocked to prevent binding of the small quantity of the urinary proteins on the urine sample.

After treatment the absorbent material is dried.

The dried material may be stored before use and, for example, sent to the patient or subject at home for use.

The absorbent material should be in a form which is easy to use. Thus for example, it may be formed on the end of a stick, or may be attached to a non-absorbent handle so that it may be held briefly in the stream of urine. A further possibility is that it is contained in a reversible bag or in a tube open at both ends. It may also be a filter paper, for example, Whatman No. 1 (Trade Mark) filter paper.

In this case, for convenience of handling, the filter paper may be folded, for example into a fan shape, and a fixing wire or string attached.

It is essential that the absorbent material incorporates an anti-bacterial agent. The material may be treated with the agent before, after or at the same time that the material is contacted with an agent which blocks urinary protein binding sites. The anti-bacterial agent prevents bacterial contamination and degradation of the constituents of the urine sample. Suitable anti-bacterial agents are boric acid, a mercury containing antiseptic agent, thiomersal and antibiotics.

The anti-bacterial agent may be in the form of an aqueous solution thereof, for example a solution of about 3% by weight boric acid.

If desired a further agent or agents may be added to prevent chemical degradation of the urine sample, for example an enzyme inhibitor to prevent glucose degradation.

The absorbent material after having had the urine applied is, of course, not dried before it is placed in the moisture impermeable container. The container may be any container which prevents egress of the urine sample.

Ideally the container should be light so that it can easily be sent by post. It may, for example, be in the form of a bag or a solid container formed from a plastics material. A suitable shape for the container is a tube, for example with a screw or otherwise sealable top. The absorbent material may be attached to a stem or handle, which is itself attached to the top. For security the moisture impermeable container may itself be enclosed in a further moisture impermeable container. Thus, for example, the absorbent material may be placed in a screw-top mailing tube, which is then placed in a bag formed from a plastic material.

When it is desired to assay the urine sample, the absorbent material may be removed from the moisture impermeable container and the urine sample recovered.

Alternatively, the material may be left in the container and the container used as the receptacle for the recovered urine sample. For example it is possible to spin the container placed in a centrifuge, and the urine sample is recovered, for example, in the bottom of the recipient tube. Suitable recovery may be obtained by centrifugation, for example at about 3000 rev/min for 10 minutes, or by pressing the absorbent material. If the absorbent material has a handle or a fixing wire or string attached, the handle or fixing wire or string may be used to support the absorbed material during centrifugation. It has been found that about 65 to 76 volume percent of the urine sample may be recovered by centrifugation.

The container used for storing the sample may be used to recover the sample, for example if it is in the form of a tube it may be used as the centrifugation tube.

The recovered urine sample may be assayed for a substance contained in the sample in the normal manner. A single assay requires, for example, about 0.1 ml of sample.

Therefore, for multiple assays of the same sample a suitable recovered sample size is from 0.5 to 1 ml. Suitable proteins for assay include human albumin and globulins.

Other substances such as creatinine, urea, uric acid, steroids and drugs and their metabolites can also be recovered and assayed by this technique.

The invention will now be further described in the following Example.

EXAMPLE Whatman No. 1 filter papers were prepared by soaking them in a solution of 0.05 wt% bovine serum albumin and 3 wt% boric acid, and air-dried before being flded into a fan shape. A fixing wire was attached to each filter paper.

The filter papers were passed through a stream of early morning urine and then placed in screw-topped mailing tubes, which were themselves each placed in a bag formed from a plastics material. The bags were mailed to a laboratory in padded envelopes, and the tubes centrifuged at 3000 revs/min for 10 minutes to recover the urine sample with the fixing wire bent over the top edge of the tube after the cap was removed and so supporting the filter paper free of the bottom of the tube. A range of 65 to 76 vol % (mean 70 vol%) of the urine samples applied to the filter papers was recovered. The albumin and creatinine content of the recovered urine were assayed.

Albumin concentration and albumin/creatinine ratios from whole and filter paper-stored urine correlated across a concentration range of 7.6 to 54.3 mg/l (r = 0.99 for each).

Although small mean differences were found between human albumin and albumin/creatinine ratios in the whole and stored samples of the same urine samples (median (range) albumin whole: 30.5 mg/l (7.6 - 54.3 mg/l) stored 31.6 mg/l (7.9 - 59 mg/l), p = 0.018; albumin/creatinine ratio whole: 7.7 mg/l (0.34 - 11.7 mg/l) stored 8.6 mg/l (0.37 - 13.7 mg/l) , p = 0.008), these differences are consistent and so small as not to present significant problems.

Claims

1. A method of storing a urine sample which comprises contacting urine with an absorbent material, which material incorporates a anti-bacterial agent, and enclosing the absorbent material in a moisture impermeable container.

2. A method according to claim 1 in which the absorbent material is a synthetic plastic material.

3. A method according to claim 2 in which the synthetic plastic material is polystyrene.

4. A method according to any one of claims 1 to 3 in which the absorbent material is in the form of a fabric.

5. A method according to claim 1 in which the absorbent material is a natural or synthetic sponge.

6. A method according to claim 1 in which the absorbent material is a filter paper which has been treated by contacting it with a agent which blocks protein binding sites such that it no longer absorbs urinary proteins.

7. A method according to claim 6 in which the agent which blocks protein binding sites is bovine serum albumin or gelatin.

8. A method according to any one of the preceding claims in which the anti-bacterial agent is boric acid, a mercury containing antiseptic agent, thiomersal or an antibiotic.

9. A method according to any one of the preceding claims in which the absorbent material also comprises an enzyme inhibitor to prevent glucose degradation.

10. A method according to any one of the preceding claims in which the absorbent material is formed on the end of a stick or attached to a non-absorbent handle.

11. A method according to any one of claims 1 to 9 in which the absorbent material is contained in a reversible bag or in a tube open at both ends.

12. A method according to any one of claims 1 to 9 in which the absorbent material is a filter paper attached to a fixing wire or string.

13. A method according to any one of the preceding claims in which the absorbent material is attached to a stem or handle which forms the top of the moisture impermeable container.

14. A method according to any one of the preceding claims in which the urine is recovered from the absorbent material.

15. A method according to claim 14 in which the urine is recovered by centrifugation or by pressing.

16. A method according to claim 15 in which the urine is recovered by centrifugation and the moisture impermeable container is used as the centrifugation tube.

17. A method according to any one of claims 14 to 16 in which the urine is assayed after recovery.

18. A method of storing a urine sample substantially as described in the Example.

19. An absorbent material suitable for use in a method as defined in any one of the preceding claims.

20. An absorbent material which incorporates an anti-bacterial agent, said absorbent material being substantially as described in the Example.