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Lecture 1- Urinalysis.docx

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Biochemistry 3386B
L.Graham Smith

Lecture 1: Urinalysis Objectives: 1. Learn the proper methods for urine specimen collection and handling 2. Understand the principles of the dipstick tests and their chemical reactions 3. Learn the diagnostic uses of these tests and some of their limitations 4. Determine how to perform urine sediment examinations by microscopy and understand some of the typical findings Why Use Urinalysis?  Non invasive, window into human metabolism  Everyone produces it  Testing is easily done, immediate  Screening test for many conditions  Unique material for producing many answers without stress to the patient Background  Urine – produced by an ultrafiltration process of blood flowing through the glomerulus in the glomerular nephrons  Ultrafiltrate Contains: o Water o Waste products o Small molecules that passed through the membrane pores  Ultrafiltrate is then also passed through: o Proximal tubule o Loop of henle o Distal tubule o Collecting Ducts o Bladder  Re-absorption of: o Water o Glucose o Salts (Electrolytes)  There are other products that are secreted into the filtrate or re-absorbed back into the plasma during passage through the LoH  This process is aided by osmotic gradients and hormonal regulation (ie. ADH and water reabsorption)  Na+/K+ ATPase is a major player Collecting and Handling Urine Urine Samples  Random: refers to a single urine sample (ie. The preferred 1 morning voiding) – store at room temperature (as long as the processing is done in 2 hours)  Timed: Several specimens collected and pooled together over a time interval (24 or 8 hours are the most common (store at 4 degrees)  Microscopic analysis: Want samples processed within 2 hours (otherwise leukocytes and renal casts rapidly disintegrate) o Specimens are discarded after 4 hours (otherwise artificial changes can take place: crystals forming, bacterial growth, metabolism of glucose, formation of ammonia, alkalization etc.)  The larger 24 hour collections will have volume measured as soon as they get to the lab, then a sample is collected and the rest is discarded  You can only do a quantitative analysis on a 24 h sample (ie. Look at concentrations) Visual Inspection Look at : 1. Clarity 2. Color 3. Odor Clarity:  Always the first step in urinalysis  Fresh Urine: o Clear o Pale Yellow o Uchrome pigments (from bilirubin)  Some urine may become cloudy due to the precipitation of urates and phosphates on refrigeration  If the cloudiness persists it may be do to a bacterial infection (increased concentrations of white blood cells) Color  Red urine might be due to : intake of certain foods, candies or medication; more likely due to the presence of blood Porphyria: A Disease  Genetic disease  Increased heme synthesis  Red wine colored urine Odor  Odor can also be used as a diagnostic marker  Ketone smell from ketoacidosis can be present in diabetic urine  Burned sugar smell can signify maple syrup urine disease (rare metabolic disease; now screened for all babies) Remember: Diabetes Insipidus = pale, thin urine; Diabetes Mellitus = sweet urine The Urine Dipstick Test  Routine analysis  Have pads impregnated with chemical reagents (specific for each test)  When dipped – change color when they react with the specimen  Intensity of color = concentration of analyte  Read off of a color chart to yield a qualitative / semi-qualitative result Multistix  10 bands Specimens Specimen Collection and Preparation  A morning specimen or a collection of clean, midstream urine  Leak-proof snap-cap vial  NO preservatives added  Dipstick screening must be done within 2 hours (to maintain its integrity) o If it cannot be done within two hours, refrigerate it to minimize bacterial growth and break down of other constituents  no microscopic analysis can be done o Refrigerated sample must be brought back to room temperature before being screened Commonly Used Automated Equipment  Clinitek 500 Analyzer o Reads the strips o Prints out the qualitative and semi-quantitative results o There is inherent variability in urine o Minimum detectable levels may vary o This analyzer allows for more consistency in the readings o Accomodates for:  Different densities  Color intensities  Acidities  Constant timing between measurements Interpretations Glucose -30s  Normal = Negative  Positive: o Diabetes Mellitus o Low renal threshold (9-10 mmol) even if blood glucose is normal o Pregnancy where gestational diabetes may be transient  the test is highly specific for glucose because glucose oxidase is the active component  very high ascorbic acid (vitamin C) can give a false negative  reactivity may vary with temperature  reactivity decreases as specific gravity increases (inverse relationship)  clinitest tablet method is sometimes used because it detects all reducing sugars (including galactose) o problem: ascorbic acid will give a positive interference Bilirubin  Normal = Negative  Only conjugated (direct reacting or water soluble) bilirubin is excreted in urine  Bilirubin seen in: o Intra-hepatic Jaundice o Extra-hepatic Jaundice o Hepatocellular Jaundice o Chronic Hepatitis o Hepatocirrhosis o Icteric stages of Dubin-Johnson and Rotor Syndromes (functional hyperbilirubinemia)  Atypical colors (unlike the ones on the block): bile pigments that mask bilirubin Ketones  Normal = Negative  Ketones are generated from the oxidation of Fatty Acids when they are used as an energy source  Detectable Levels: o Conditions of stress o Exercise o Fasting o Pregnancy o Hyperemesis gravidarum o Febrile states o Alcohol intoxication o Abnormalities in carbohydrate and lipid metabolism  Large quantities are produced in Diabetic Keto-Acidosis (DKA)  Test reacts with acetoacetic acid in the urine  It does NOT react with: acetone or B-hydroxybutyric acid  high specific gravity and low pH urines may give “trace results” o false positives (trace or less) may occur in highly pigmented urine Specific Gravity  Normal = 1.010 – 1.025  Specific gravity indicates the degree of concentration of the urine  Early morning samples = higher specific gravity  Measure of the concentrating ability of the renal tubules  Low specific gravity in people with polydipsia and diabetes insipidus  High values in: o Dehydration following severe illness o Severe exercise  Stick method is affected by high pH values  To increase the accuracy of this me
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