A urine test strip or dipstick is a basic diagnostic tool used to determine pathological changes in a patient's urine in standard urinalysis. + Urine test stripLeukocytes Nitrite Urobilinogen Protein pH Haemoglobin Specific gravity Ketone Bilirubin Glucose A standard urine test strip may comprise up to 10 different chemical pads or reagents which react (change color) when immersed in, and then removed from, a urine sample. The test can often be read in as little as 60 to 120 seconds after dipping, although certain tests require longer. Routine testing of the urine with multiparameter strips is the first step in the diagnosis of a wide range of diseases. The analysis includes testing for the presence of proteins, glucose, ketones, haemoglobin, bilirubin, urobilinogen, acetone, nitrite and leucocytes as well as testing of pH and specific gravity or to test for infection by different pathogens.
The test strips consist of a ribbon made of plastic or paper of about 5 millimetre wide. Plastic strips have pads impregnated with chemicals that react with the compounds present in urine producing a characteristic colour. For the paper strips the reactants are absorbed directly onto the paper. Paper strips are often specific to a single reaction (e.g. pH measurement), while the strips with pads allow several determinations simultaneously.
There are strips which serve different purposes, such as qualitative strips that only determine if the sample is positive or negative, or there are semi-quantitative ones that in addition to providing a positive or negative reaction also provide an estimation of a quantitative result, in the latter the colour reactions are approximately proportional to the concentration of the substance being tested for in the sample. The reading of the results is carried out by comparing the pad colours with a colour scale provided by the manufacturer, no additional equipment is needed.http://www.seg-social.es/ism/gsanitaria_es/ilustr_capitulo6/cap6_7_analisorina.htm language = Spanish
This type of analysis is very common in the control and monitoring of diabetic patients. The time taken for the appearance of the test results on the strip can vary from a few minutes after the test to 30 minutes after immersion of the strip in the urine (depending on the brand of product being used).
Semi-quantitative values are usually reported as: trace, 1+, 2+, 3+ and 4+; although tests can also be estimated as milligrams per decilitre. Automated readers of test strips also provide results using units from the International System of Units.
Test method The test method consists of immersing the test strip completely in a well mixed sample of urine for a short period of time, then extracting it from the container and supporting the edge of the strip over the mouth of the container to remove excess urine. The strip is then left to stand for the time necessary for the reactions to occur (usually 1 to 2 minutes), and finally the colours that appear are compared against the chromatic scale provided by the manufacturer.
An improper technique can produce false results, for example, leukocytes and erythrocytes precipitate at the bottom of the container and may not be detected if the sample is not properly mixed, and in the same way, if an excess of urine remains on the strip after it has been removed from the test sample, may cause the reagents to leak from the pads onto adjacent pads resulting in mixing and distortion of the colours. To ensure that this does not occur it is recommended the edges of the strip are dried on absorbent paper.
Reactions for generalised tests
pH
The lungs and kidneys are the main regulators of an organism's acid / alkali balance. The balance is maintained through the controlled excretion of acidic hydrogens in the form of ammonia ions, monohydrogenated phosphate, weak organic acids and through the reabsorption of bicarbonate through glomerular filtration in the convoluted tubules of the nephron. The pH of urine normally vary between 4.5 and 8 with the first urine produced in the morning generally being more acidic and the urine produced after meals generally more alkaline. Normal reference values are not provided for urine pH as the variation is too wide and results have to be considered in the context of the other quantifiable parameters.
The determination of urinary pH has two main objectives, one is diagnostic and the other is therapeutic. On the one hand it provides information regarding the balance between acid and alkali in a patient and allows identification of the substances that are present in the urine in crystalline form. On the other hand, certain illnesses require a patient to keep the pH of their urine within given narrow margins, whether to promote the elimination of chemotherapeutic agents, avoid the precipitation of salts that promote the formation of kidney stones, or in order to facilitate the control of a urinary infection. Regulating diet mainly controls urinary pH, although using medication can also control it. Diets rich in animal proteins tend to produce acidic urine, while diets mainly composed of vegetables tend to produce alkali urine.
Commercial brands measure pH in increments of 0.5 or 1 pH units between pH 5 and 9. In order to differentiate pH in this wide range it is common to use a double indicator system comprising methyl red and bromothymol blue.ADW Diabetes. Methyl red produces a colour change from red to yellow in the range of pH 4 to 6 and the bromothymol blue changes from yellow to blue between pH 6 and 9. In the range 5 to 9 the strips show colours that change from orange at pH 5, passing through yellow and green to dark blue at pH 9.
Specific gravity
One of the kidneys' important functions is to reabsorb water after glomerular filtration. The complex process of reabsorption is usually one of the first renal functions to be affected by disease. The specific gravity of urine is a measure of its density compared to H2O and depends on the quantity and density of solutes (molecules with more mass per volume increase measure of specific gravity). The measurement of specific gravity should not be confused with the measurement of osmotic concentration, which is more related to the number of particles than with their mass.
The urine test strip test for specific gravity is based on the change in dissociation constant (pKa) of an anionic polyelectrolyte (poly-(methyl vinyl ether/maleic anhydride)) in an alkali medium that is ionised and releases hydrogen ions in proportion to the number of cations present in the solution. The greater the cation concentration of the urine the more hydrogen ions are released, thereby reducing the pH. The pad also includes bromothymol blue, which measures this change in pH. It should be remembered that the test strip only measures cation concentration, it is therefore possible that urine with a high concentration of non-ionic solutes (such as glucose or urea) or with high molecular weight compounds (such as the media used to provide radiographic contrast) will yield a result that will be erroneously lower than that measured by densitometry. The colours vary from dark blue with a reading of 1.000 to yellow for a reading of 1.030. In an alkaline medium Polyelectrolyte-Hn + Cationsn+ → Polyelectrolyte-Cations + nH+ In an alkaline mediumH+ + Bromothymol blue(Blue) → Bromothymol blue-H+(Yellow) Elevated protein concentrations produce slightly elevated specific density results as a consequence of the indicator's protein error; in addition, samples with a pH above 6.5 give lower readings as a result of the indicator's bias. For this reason the manufacturers recommend that 5 units are added to the specific gravity reading when the pH is greater than 6.5.
Blood Blood may be present in the urine either in the form of intact red blood cells (hematuria) or as the product of red blood cell destruction, hemoglobin (hemoglobinuria). Blood present in large quantities can be detected visually. Hematuria produces cloudy red urine, and hemoglobinuria appears as a clear red specimen. Any amount of blood greater than five cells per microliter of urine is considered clinically significant; visual examination cannot be relied upon to detect the presence of blood. Microscopic examination of the urinary sediment shows intact red blood cells, but free hemoglobin produced either by hemolytic disorders or lysis of red blood cells is not detected. Therefore, chemical tests for hemoglobin provide the most accurate mean for determining the presence of blood. Once blood has been detected, the microscopic examination can be used to differentiate between hematuria and hemoglobinuria.
Chemical tests for blood use the pseudoperoxidase activity of hemoglobin to catalyze a reaction between the heme component of both hemoglobin and myoglobin and the chromogen (a substance that acquires colour after a chemical reaction) tetramethylbenzidine to produce an oxidized chromogen, which has a green-blue colour. Reagent strip manufacturers incorporate peroxide, and tetramethylbenzidine, into the blood testing area. Two colour charts are provided that correspond to the reactions that occur with hemoglobinuria, myoglobinuria and hematuria (RBCs). In the presence of free hemoglobin/myoglobin, uniform colour ranging from a negative yellow through green to a strongly positive green-blue appears on the pad. In contrast, intact red blood cells are lysed when they come in contact with the pad, and the liberated hemoglobin produces an isolated reaction that results in a speckled pattern on the pad. Reagent strip tests can detect concentrations as low as five red blood cells per microliter; however, care must be taken when comparing these figures with the actual microscopic values, because the absorbent nature of the pad attracts some of urine. The terms trace, small, moderate, and large (or trace, 1+, 2+, and 3+) are used for reporting.
False-positive reactions due to menstrual contamination may be seen. They also occur if strong oxidizing detergents are present in the specimen container. Vegetable peroxidase and bacterial enzymes, including an Escherichia coli peroxidase, may also cause false-positive reactions. Therefore, sediments containing bacteria should be checked closely for the presence of red blood cells. Traditionally, ascorbic acid (vitamin C) has been associated with false-negative reagent strip reactions for blood. Both Multistix and Chemstrip have modified their reagent strips to reduce this interference to very high levels of ascorbic acid, and Chemstrip overlays the reagent pad with an iodate-impregnated mesh that oxidizes the ascorbic acid prior to its reaching the reaction pad. False-negative reactions can result when urine with a high specific gravity contains crenated red blood cells that do not lyse when they come in contact with the reagent pad. Decreased reactivity may also be seen when formalin is used as a preservative or when the hypertension medication captopril or high concentration of nitrite are present. Red blood cells settle to the bottom of the specimen container, and failure to mix the specimen prior to testing causes a falsely decreased reading.Urinalaysis and Body Fluids Sixth Edition by Susan King Strasinger and Marjorie Schaub Di Lorenzo
Diseases identified
With the aid of routine examinations early symptoms of the following four groups can be identified: Diseases of the kidneys and the urinary tract Carbohydrate metabolism disorders (diabetes mellitus) Liver diseases and haemolytic disorders Urinary infections
Urinary tract