Chemical Examination of Urine Chapter 6 PDF

6/20/2024 Chemical Examination of Urine Chapter 6 1 1 Preamble PowerPoints are a general overview and are provided to help students take notes over the video le...

6/20/2024 Chemical Examination of Urine Chapter 6 1 1 Preamble PowerPoints are a general overview and are provided to help students take notes over the video lecture ONLY. PowerPoints DO NOT cover the details needed for the Unit exam Each student is responsible for READING the TEXTBOOK for details to answer the UNIT OBJECTIVES Unit Objectives are your study guide (not this PowerPoint) Test questions cover the details of UNIT OBJECTIVES found only in your Textbook! 2 1  6/20/2024 Reagent Strips Reagent strips provide a simple, rapid means for performing routine chemical tests on urine Single and multitest strips available The brand and number of tests used are a matter of laboratory preference Specified by urinalysis instrumentation manufacturers Strips consist of chemical-impregnated absorbent pads on a plastic strip 3 Reagent Strips (continued_1) A color-producing chemical reaction takes place when the absorbent pad comes in contact with urine The reactions are interpreted by comparing the color produced on the pad within the required time frame with a chart supplied by the manufacturer Several degrees of color are shown to provide semiquantitative readings of neg, trace, 1+, 2+, 3+, and 4+ Estimates of mg/dL are also provided for many of the test areas 4 2  6/20/2024 Reagent Strips (continued_2) Urine reagent strips pH Protein Glucose Ketones Blood Bilirubin and urobilinogen Nitrate and leukocytes Specific gravity 5 Reagent Strip Technique Dip strip briefly into well-mixed specimen at room temperature Remove excess urine by touching edge of strip to container as strip is withdrawn Blot edge of strip on absorbent pad Wait specified amount of time Read using a good light source 6 3  6/20/2024 Improper Technique Errors Formed elements such as red and white blood cells sink to the bottom of the specimen and will be undetected in an unmixed specimen Allowing the strip to remain in the urine for an extended period may cause leaching of reagents from the pads Excess urine remaining on the strip after its removal from the specimen can produce a runover between chemicals on adjacent pads, producing distortion of the colors 7 Improper Technique Errors (continued_1) The timing for reactions to take place varies between tests and manufacturers; the manufacturer’s stated time should be followed A good light source is essential for accurate interpretation of color reactions The strip must be held close to the color chart without actually being placed on the chart; reagent strips and color charts from different manufacturers are not interchangeable Specimens that have been refrigerated must be allowed to return to room temperature prior to reagent strip testing 8 4  6/20/2024 Handling and Storing Reagent Strips Store with desiccant in an opaque, tightly sealed container Remove strips immediately prior to use Do not expose to volatile fumes Store below 30°C Do not use past the expiration date Visually inspect for discoloration/deterioration 9 Quality Control of Reagent Strips Run positive and negative controls, usually at the beginning of a shift Run additional controls When a new bottle of strips is opened When results are questionable When there are concerns over strip integrity Record control results Manufactured positive and negative controls are available Do not use distilled water as a negative control as reactions are designed for urine ionic concentration All negative control readings should be negative Positive control readings should agree with published control values Be aware of manufacturer-stated limitations and interfering substances 10 5  6/20/2024 Confirmatory Testing Confirmatory tests use different reagents or methodologies to detect the same substances as reagent strips with the same or greater sensitivity or specificity Nonreagent strip testing procedures using tablets and liquid chemicals may be available when questionable results are obtained Chemical reliability of these procedures also must be checked using positive and negative controls 11 Urine pH Lungs and kidneys are major regulators of acid-base content First morning specimen slightly acidic at 5.0 to 6.0 Postprandial specimen more alkaline Normal range is 4.5 to 8.0 No absolute values are assigned Considerations include Acid-base content of the blood Patient’s renal function Presence of a urinary tract infection Patient’s dietary intake Age of the specimen 12 6  6/20/2024 Clinical Significance of Urine pH Respiratory or metabolic acidosis/ketosis Respiratory or metabolic alkalosis urine is alkaline Renal calculi formation Treatment of urinary tract infections Precipitation/identification of crystals High-protein diets=acidic urine Low-protein diets=alkaline urine A pH above 8.5 is associated with a specimen that has been preserved improperly and indicates that a fresh specimen should be obtained to ensure the validity of testing 13 pH-Reagent Strip Reactions Needed to measure between 5.0 and 9.0 in one half or one unit increments Double-indicator system reaction Methyl red = 4 to 6 red/orange to yellow Bromthymol blue = 6 to 9 green to blue Methyl red + H+ → Bromthymol blue − H+ (Red/Orange → Yellow) (Green → Blue) Interference No known substances interfere with urinary pH measurements performed by reagent strips 14 7  6/20/2024 Protein Most indicative of renal disease Proteinuria seen in early renal disease Normal = 25 mg/dL High SG/crenated cells Formalin Captopril High concentrations of nitrite Unmixed specimens 59 Bilirubin Urine bilirubin early indicator of liver disease Normal degradation product of hemoglobin RBCs destroyed by liver and spleen following 120-day life span Body recycles iron, protein Protoporphyrin is broken down into bilirubin Bilirubin is bound to albumin Kidneys cannot excrete Unconjugated bilirubin: water insoluble 60 30  6/20/2024 Bilirubin (continued) Conjugated bilirubin: water soluble Unconjugated bilirubin to the liver Conjugated with glucuronic acid Forms conjugated bilirubin From liver to intestines Reduced to urobilinogen, stercobilinogen, and urobilin by intestinal bacteria Excreted in feces Bilirubin Metabolism 61 Bilirubin Clinical Significance Conjugated bilirubin appears in urine with bile duct obstruction, liver disease or damage Obstruction: bilirubin backs up into circulation and is excreted in urine No urobilinogen is formed Hepatitis, cirrhosis: conjugated bilirubin leaks back into circulation from damaged liver; some bilirubin passes to intestine Detection of bilirubin can also be used in determining the cause of clinical jaundice 62 31  6/20/2024 Bilirubin Reagent Strip Reactions Principle is a diazo reaction Report: neg, small (1+), moderate (2+), large (3+) Colors may be difficult to interpret Easily influenced by other pigments present in the urine Atypical colors can be problem for automated readers acid bilirubin glucuronide + *diazonium salt-------- azodye (tan or pink to violet) * diazonium salt- (2,4-dichloroaniline diazonium salt or 2,6-dichlorobenzene-diazonium-tetrafluoroborate) 63 Bilirubin Reaction Interference False-positive Urine pigments Pyridium (phenazopyridine) Drugs indican, Lodine False-negative Old specimens (biliverdin does not react) Ascorbic acid >25 mg/dL Nitrite Combine with diazonium salt and block bilirubin reaction 64 32  6/20/2024 Ictotest Tablets Confirmatory for bilirubin Tablets containing p-nitrobenzene-diazonium-p-toluenesulfonate, SSA, sodium carbonate, and boric acid Use specified mat for test; mat keeps bilirubin on surface for reaction Positive reaction = blue-to-purple color Interfering substances are washed into the mat, and only bilirubin remains on the surface 65 Urobilinogen Bilirubin in intestine converted to urobilinogen and stercobilinogen Urobilinogen is reabsorbed into circulation and stercobilinogen is not = urobilin Pigments responsible for the characteristic brown color of feces There is always a small amount of urobilinogen filtered by the kidneys and is found in the urine