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Tests on specimens of urine or
stools
In this fourth article in a series on clinical testing, Pamela Mason focuses on common urine and faecal tests that pharmacists may encounter




                                                                                                                Identify knowledge gaps
                                                                                                                1. List three substances that can be measured
                                                                                                                    in urine.
                                                                                                                2. Why is mid-stream urine collected?
                                                                                                                3. List two tests performed on stools.


                                                                                                                Before reading on, think about how this article
                                                                                                                may help you to do your job better. The Royal
                                                                                                                Pharmaceutical Society’s areas of competence
                                                                                                                for pharmacists are listed in ―Plan and record‖,
                                                                                                                (available at: www.rpsgb.org/education). This
                                                                                                                article relates to ―diagnostic tests‖ and
                                                                                                                ―therapeutic drug monitoring‖ (see appendix 4 of
                                                                                                                ―Plan and record‖).


     xamation of urine for signs of disease has    results of some tests. For example, a container            catheter tubing, using a sterile syringe. Urine

E    been a diagnostic practice for many
     centuries. For example, according to
                                                   contaminated with chlorhexidine can result
                                                   in false positive results for protein. It is, there-
                                                                                                              from catheter bags can be several hours old
                                                                                                              and should not be used for testing.
Hippocrates blood or pus in the urine indi-                 freelance journalist and author, based in         fore, best for the patient to be supplied with a
cated ulceration either of the kidneys or of                Monmouthshire                                     container specifically for the purpose of
the bladder. Today, urine and stools can                                                                      specimen collection.
provide information not only about the                                                                           Pharmacists need to be sensitive to the fact
                                                   544    The Pharmaceutical Journal (Vol 272)   1 May 2004
kidneys, bladder and gastrointestinal tract, but                                                              that people can have different attitudes towards
also about a wide range of other conditions.                                                                  handling or talking about body fluids and it is
                                                                                                              important for privacy to be maintained.
Urinalysis
Urine is produced by the kidneys to remove                                                                    Midstream specimens Most tests require
soluble waste substances from the body.These                                                                  that the urine specimen is collected ―mid-
can be detected using dipstick methods (eg,                                                                   stream‖ (also known as ―clean-catch‖ speci-
tests for pregnancy or diabetic ketoacidosis)                                                                 mens). This is so that the specimen is not
or, if more detailed information is required,                                                                 contaminated by bacteria surrounding the ure-
urine can be sent for laboratory analysis.                                                                    thra — often, these bacteria can be the same as
     Some substances can be measured in blood                                                                 those causing a urinary tract infection (UTI),
or urine (eg, glucose).The main advantage of                                                                  so can result in a false positive result. First, the
tests on urine is that they are relatively non-                                                               skin around the urethra must be cleaned. The
invasive compared with blood tests. However,                                                                  patient then urinates, pauses, then urinates
if the urine specimen is collected incorrectly,                                                               again into the specimen container.
this can affect test results. The correct proce-                                                                 Not everyone is able to collect their own
dure for collection needs, therefore, to be                                                                   specimen, particularly if a midstream speci-
explained clearly. It is important that any                                                                   men is required. Parents may need to help a
container used to collect a urine specimen is                                                                 child hold the container (urine collection
clean and contains no traces of detergent or                                                                  bags are used for babies) and people with
disinfectant because these can affect the                                                                     disabilities or illness may need the help of a
                                                                                                              carer. Gloves should be provided to protect
         Pamela Mason, PhD, MRPharmS, is   a                                                                  the person collecting the specimen as well as
to prevent cross contamination. In hospital,   Visual examination The appearance and
specimens may need to be collected from        odour of urine can also suggest health prob-
                                               lems. Normal urine is a clear, straw-coloured
                                               fluid and, often, simply examining a specimen
                                               visually can provide evidence of an infection
                                               or disease. Like other bacterial infections,
                                               UTIs are associated with the recruitment of
                                               the white blood cells to the site of infection.
                                               Pus is formed, which causes urine to become
                                               cloudy. However, cloudy urine is not always a
                                               sign of a UTI and clear urine does not always
                                               rule out infection.
                                                  Patients who are jaundiced will have dark
                                               yellow, orange or brown urine because of the
                                               excess bile (often accompanied by pale stools
                                               and yellow skin). Blood can colour urine red
                                               (indicating disease) as can the rare, inherited
                                               disorder porphyria. Some foods, such as beet-
                                               root and asparagus, can also affect the colour
                                               of urine. Drugs that change urine colour
                                               include: levodopa (red), rifampicin (red),
                                               triamterene (blue-green) and vitamin B
                                               complex (dark yellow). Freshly voided urine
                                               has almost no smell, whereas infected urine
                                               has a fishy odour. Urine from people with
                                               anorexia can smell of pear drops.
                                                  Pharmacists asked for advice on abnormal
                                               urine colour should check that it is not diet-

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                                                                                                 Mik e Wyndham Medical P Library
                                                                                                                  icture
                                                                                                                                                 CPD
or drug-related. Change
that cannot be clearly                                                                                            Panel 2: Dipstick test results
attributed to foods or
medicines,       or that             is                                                                           Bilirubin The presence of bilirubin in urine can
accompanied by unex-                                                                                              suggest biliary disease.
plained symptoms, should
be referred to a GP.                                                                                              Blood Blood is not usually present in urine.
                                                                                                                  Haematuria (blood in the urine) can be caused by
Dipstick tests         Reagent                                                                                    renal conditions (such as glomerulonephritis),
strips, or ―dipsticks‖, are                                                                                       carcinoma and vasculitis (eg, endocarditis,
strips of plastic, with test                                                                                      systemic lupus erythmatosus or other connective
areas treated with chemi-                                                                                         tissue diseases). It can also be caused by
cal reagents. For example,                                                                                        infection (eg, cystitis, prostatitis and urethritis),
a Clinistix strip is impreg-                                                                                      bladder catheterisation, calculi and the use of
nated        with       glucose                                                                                   cyclophosphamide.
oxidase and an indicator                                                                                             Urine can also be examined for the presence
substance        (o-toluidine)                                                                                    of red and white blood cells under a microscope.
which is oxidised to vari-                  Dipstick and colour chart must be closely compared
ous shades of blue-green,                                                                                         Glucose Glycosuria (sugar in the urine) can be
depending on the amount of glucose present.                  result in microbial contamination and this           caused by diabetes mellitus, pregnancy, sepsis or
Most pharmacists will be familiar with the                   can affect test results (eg, bacterial consump-      renal tubular damage (ie, abnormal renal
dipsticks used by people with diabetes who                   tion of glucose can give a false negative).          absorption).
find blood glucose monitoring difficult (eg,                 However, samples should be allowed to
Diabur-test 5000), dipsticks used to detect                  return to room temperature before testing.           Ketones Ketones are breakdown products of fats
diabetes and those popular with people on                    Pharmacists can also advise patients on              and their presence in urine can indicate anorexia,
the Atkins diet (eg, Ketostix, see PJ,       27 July         keeping records of their test results.               dieting or diabetes that is poorly controlled.
2002, pp135–7). Dipstick testing is simple,                     In addition to contamination, diet and
convenient and offers quick results. Tests can               medicines can also sometimes cause false             Leucocytes A significant increase in white cell
be performed at home, in surgeries or                        negatives or false positives. For example, a         numbers is evidence of infection, which can be
hospitals and in pharmacies.                                 high ascorbic acid concentration in urine can        confirmed by urine culture.
    Various dipsticks are available to detect                give false negative results with Clinistix.
substances such as glucose, protein and blood.               Drugs containing azo dyes (eg, nitrofuran-           Nitrites Nitrites in urine indicate infection. The first
Multiple reagent strips are also available. For              toin) can also affect the readability of the         morning urine, or urine passed at least four hours
example, Multistix 10 SG strips test for biliru-             reagent area.                                        after last urinating, is the best specimen to use.
bin, blood, glucose, ketones, leukocytes,
nitrite, pH, protein, specific gravity and uro-              Urinary tract infections Assuming that the           pH Bacteria will usually increase the pH of urine
bilinogen, to give a comprehensive urinalysis                urine has been collected appropriately (ie, it       because they break down urea to ammonia,
profile. However, not all of these reagent                   is not contaminated with the bacteria                which combines with hydrogen ions. In terms of
strips are prescribable on NHS prescriptions.                normally present in the lower third of the           monitoring acid-base imbalance in the body,
    Pharmacists can advise patients, who need                urethra or anogenital area), bacteria in the         serum pH is generally a better measure than
to test their urine regularly to follow the                  urine indicates a UTI. The dipstick method           urine pH.
manufacturer’s instructions on the storage of                for detecting UTIs is based on the fact that all          Acidic urine is associated with uric acid and
reagent strips as well as use. These should be               common bacteria causing UTIs convert                 calcium oxalate stones. Alkaline urine is
kept in their original container (which often                nitrate to nitrite.Thus, an increase in urinary      associated with calcium carbonate, calcium
contains a dessicant) and the expiry date                    nitrite concentration indicates bacterial            phosphate, and magnesium phosphate stones.
should be checked. Usually, reagent strips                   infection. In addition, the enzyme leucocyte         Risks can, therefore, be lowered by modifying
should be discarded six months after the                     esterase indicates the presence of white cells       urine pH accordingly.
container is opened. General instructions for                and detection of this enzyme provides further            Ideally, pH tests should be performed
testing are given in Panel 1.                                evidence of infection. Dipsticks for UTIs            immediately after urine collection. The specimen
    If urine cannot be tested within an hour of              usually consist of at least two reagent squares,     container must be covered to prevent the escape
urinating,      it should       be refridgerated.            one for detecting nitrite and the other for          of carbon dioxide.
Prolonged exposure to room temperature can                   detecting the enzyme.
                                                                 Although convenient, these            dipstick   Protein Proteinuria (protein in the urine) can be
                                                             methods are limited by the number of false           caused by urinary tract infection, diabetes
  Panel 1: Dipstick procedure                                positives they generate so positive results          mellitus, glomerulonephritis, nephrosis, pyrexia
                                                             should always be submitted for urine culture         and pregnancy. A morning specimen is best for
  ■   Dip the reagent strip into the urine, making           (which can take at least two days) to confirm,       detecting levels outside the reference range.
      sure that the reagent area is completely               reliably, the presence of bacteria. A negative
      immersed                                               dipstick result, however, is strong evidence         Specific gravity Increased urine specific gravity
  ■   Take the strip out immediately, removing               that the patient does not have a UTI.                can indicate dehydration, diarrhoea, glucosuria,
      excess urine by gently tapping the strip                   Other conditions that dipstick tests can         heart failure (decreased blood flow to the
      against the side of the specimen container             indicate are shown in Panel 2.                       kidneys) or renal arterial stenosis. Decreased
  ■   At a prescribed time after dipping the strip                                                                urine specific gravity can suggest excessive fluid
      into the specimen (eg, 30 seconds for Diastix          pH The body’s control of urine pH is not as          intake, diabetes insipidus, glomerulonephritis or
      and 10 seconds for Clinistix), closely compare         strict as its control of blood pH. Conditions        pyelonephritis.
      the colour of the test area with the colour            associated with high or low pH are listed in
      chart provided                                         Panel 2. The efficacy of some medicines is           Urobilinogen Small      amounts of urobilinogen are
  ■   After testing, urine can be disposed of in a           affected by acidic or alkaline environments so       usually present in urine, but raised levels suggest
      toilet                                                 pH can be used to select the most appropri-          liver disease.
                                                             ate treatment for a UTI. For example, strep-

www.pjonline.com                                                                                                   1 May 2004      The Pharmaceutical Journal (Vol 272)      545
                     CPD
tomycin and neomycin are more effective in                 diarrhoea is the result of antibiotic use. This
treating UTIs when urine is alkaline.                      bacterium grows excessively when antibiotics           Action: practice points
                                                           alter the balance of colonic bacterial flora and
Specific gravity The specific gravity of urine is          can cause pseudomembranous colitis.                    Reading is only one way to undertake CPD and the
a measure of the amount of substances                         Recently, a stool antigen test for Helicobacter     Society will expect to see various approaches in a
dissolved in the urine (g/ml). It primarily                pylori infection has become available.                 pharmacist’s CPD portfolio.
indicates how well the kidneys are function-                                                                      1. Familiarise yourself with the range of
ing to adjust the amount of water in urine.                Microscopy and stool cultures              Stool           dipsticks available and how they should be
                                                           specimens can be examined for the presence                 used.
24-hour urine tests           Urine is sometimes           of GI infective organisms, such as those               2. Revise the symptoms of bowel cancer and
collected over 24 hours in order to measure a              causing food poisoning (eg,           Salmonella           consider how you would advise a patient with
number of metabolites, such as calcium,                    species, Staphylococcus aureus and Clostridium            a change in bowel habit or stool appearance.
creatinine, nitrogen, oxosteroids, potassium,              botulinum), shigella, cholera and giardia. A           3. Make a list of the drugs that can alter the
sodium, urea and urate.The accuracy of such                small amount of stool is smeared on to a                   colour of urine or stools and be sure to
measurements depends, mainly, on the                       microscope slide and a Gram stain is per-                  counsel patients about this.
accuracy of the urine collection.                          formed. The stained smear is then examined
    For a 24-hour urine collection required                under the microscope for the presence of
from 9am on Tuesday, the patient should be                 bacteria. The colour, size and shape of cells          Evaluate
asked to empty the bladder completely at                   allow identification of infecting organisms.           For your work to be presented as CPD, you need to
9am and discard this specimen. Urine in the                   Infections can also be identified by placing        evaluate your reading and any other activities.
bladder at the start of the test must not be in-           a small stool sample in culture media and              Answer the following questions: What have you
cluded in the collection.All urine passed after            observing bacterial growth.                            learnt? How has it added value to your practice?
this point is collected. At 9am on Wednesday                                                                      (Have you applied this learning or had any
the bladder should be emptied completely                   Faecal occult blood          Blood in the stool        feedback?) What will you do now and how will this
and this final specimen added to the collec-               can come from anywhere along the digestive             be achieved?
tion, which is given to the health care profes-            tract, from the mouth to the anus. Some con-
sional carrying out the analysis. Analysis must            ditions, such as GI ulcers, are associated with
be performed within one hour of collection.                heavy bleeding.This can result in stools being       colorectal cancer and positive results are
                                                           black or ―tarry‖. A black stool usually means        bound to cause anxiety. Oral iron prepara-
Stool tests                                                that the blood has come from the upper part          tions can also give false positive results. In
A lot of information about a person’s diet and             of the GI tract (ie, the oesophagus, stomach or      addition to NSAIDs, drugs that can cause GI
general state of health can be gained from                 duodenum) because exposure to digestive              bleeding include anticoagulants, colchicine
stools. For example, a change in dietary habits            juices turns the blood black. Stomach or duo-        and corticosteroids. Other factors that can
can lead to an increase in the amount of gas               denal ulcers caused by non-steroidal anti-           cause inaccurate FOB test results include
produced by gastrointestinal (GI) bacteria, as             inflammatory drugs are common causes of              eating red meat, fish, turnips or horseradish
can acute GI infections (increased gas in the              upper GI bleeds. Other causes include gastri-        within three days of the test.
intestines due to the rapid movement of food               tis and oesophageal varices. Taking iron                Screening of asymptomatic people over 45
through the gut) and excessive flatus and stools           supplements or bismuth-containing medicines          years of age shows that 2 per cent of people
that float are generally associated with these             (such as Pepto-Bismol) can also blacken stools.      test positive. Of these, one in 10 will have a
conditions. Floating stools can, however, also                Bleeding in the lower GI tract can result in      carcinoma and one in three an adenoma. A
be associated with malabsorption syndromes.                maroon or bright red, bloody stools. Causes          series of two or three samples taken over
Increased levels of nutrients in the stool (due            include haemorrhoids, anal fissures, diverticu-      several days may be a more definite way of
to malabsorption in the GI tract) are supplied             lar bleeding, bacterial enterocolitis, inflamma-     detecting bleeding in the gut, so sometimes a
to GI bacteria, which produce more gas.                    tory bowel disease, colon polyps and colon           patient might be asked to supply three stool
    Bile salts (made by the liver) give stool its          cancer. People with such symptoms must be            samples for laboratory testing. It should be
a normal brown colour. Cholestasis or liver                referred to their GP.                                remembered that the earlier that diseases, like
infections like viral hepatitis may produce                   Small amounts of blood in stools may not          bowel cancer, are detected the better the
clay coloured stools. Pharmacists asked for                be visible but an FOB test should detect this.       prognosis. Some health care professionals
advice on a change in stool characteristics                FOB tests are mainly used to screen for              recommend that all people over 50 years old
should refer patients to a GP if the change has            colorectal cancers and polyps. Such tests are        should have an annual test for FOB.
persisted for more than two weeks or if                    also used in people with persistent abdominal
blood, fever, or dizziness accompanies these               symptoms (eg, pain). There are two types of          Faecal urobilinogen            Urobilinogen is
changes. It is likely that the patient will be             FOB test. The traditional guaiac smear test          produced in the small intestine by the action
asked to collect a stool sample for further                involves smearing a sample onto a card,              of the intestinal bacteria on bile and it is the
investigation.                                             adding a testing solution and observing a            compound which gives the stool its brown
    Commonly, stool tests look for blood,                  colour change (green). Flushable reagent pads        colour. Increased faecal urobilinogen levels
urobilinogen and fat or infection. For exam-               are also now available. These are convenient         are found where there is increased haemoly-
ple, a faecal occult blood (FOB) test can be               for home use and there is no stool handling.         sis of red blood cells. Decreased levels suggest
requested if a patient has unexplained                     Many health care providers, however, favour          obstructive biliary disease.
anaemia. If a parasitic infestation is suspected           guaiac tests because these were used in the
(eg, in prolonged diarrhoea of unknown                     large studies that have shown the benefits of        Faecal fat Tests for faecal fat are used to
cause or other intestinal symptoms) stools are             colon cancer screening.                              help diagnose malabsorption syndromes (eg,
examined for parasites and ova.                               Although safe and inexpensive, FOB tests          pancreatic disease with a deficiency of lipase
    Less common stool tests include the                    are limited by the fact that colorectal cancers      and biliary obstruction). If there is steator-
detection of proteolytic enzymes (trypsin and              bleed intermittently so tests can give false         rhoea (excess fat in the stools), stools will be
chymotrypsin) in young children suspected of               negatives. Large amounts of vitamin C can            frothy, foul smelling and greasy.This indicates
having cystic fibrosis. Another example is a               also cause false-negative results. Moreover,         that fats are not being digested.
stool test to detect toxins produced by                    other lesions can cause blood to be present in          It is a misconception that floating stools
Clostridium difficile, particularly in hospital            stools (even bleeding gums following a dental        are caused by an increase in the fat content of
patients when there is a suspicion that                    procedure), so the test is non-specific for          the stool.

546    The Pharmaceutical Journal (Vol 272)   1 May 2004                                                                                         www.pjonline.com

				
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