Urinalysis and other Renal Labs

What is Urinalysis (UA)? “Urinalysis is the physical, chemical, and microscopic examination of urine. It involves a number of tests to detect and measure various compounds that pass through the urine.” UA is the best way to physically examine the kidney

What is UA? 95 % water, 5 % solids 3 main components :  Water  Urea  NaCl Urine color  pigments urochrome + urobilin  Intensity of color parallels degree of contamination

Preparation Clean catch: clean-voided midstream specimen into non-sterile container  External genitalia should be cleansed (at least in females) Urine is a body fluid, and should be handled as such  Lab examination should occur within minutes if held at room temperature  Should be at least ml in volume to investigate Evaluation of un-spun urine (appearance, sp. gravity, chemical testing) Centrifugation ( rpm for 3-5 minutes)  Decant supernatant, resuspend sediment in the urine that remains on the sides of the tube, and place a drop on a clean slide for microscopic evaluation of sediment

Indications for UA Suspect or confirm Urinary Tract Infection (UTI) Rule out primary renal disease Rule out systemic disease with renal manifestations Assess complications of hypertension Assess presence or amount of endogenous or exogenous excreted substances

Components of the Basic UA Color / appearance Chemistries  Protein  Glucose  Ketones  Bilirubin / urobilinogen  Hemoglobin / blood  Nitrite  Leukocyte esterase Specific gravity pH Microscopic exam  Cells / casts  Bacteria  Other organisms  Crystals

Other Tests Gram stain Urine Culture Acid-fast stain Protein electrophoresis Antigen detection (immunofluorescence)

Visual Inspection of Urine Color: usually light to dark yellow, depending on concentration of the urinary pigments urochrome, urobilin, and uroerythrin  Color can be altered by:  Disease  Drugs  Food Appearance:  Turbidity: Can be due to cells, bacteria, or mucous  Amorphous phosphates (white precipitate) in alkaline urine, or amorphous urates (pink precipitate) in acid urine

Abnormal Colors in Urine Red:  Heme pigment or hematuria, drugs and food can also affect Brown:  Heme pigment--hemeglobin or myoglobin Orange/Yellow:  Bilirubin, urobilin but also carrots, pyridium, nitrofurantoin White:  Pyuria, phosphates, chyluria, propofol

Abnormal Colors in Urine Blue/Green:  Methylene blue, propofol, amitriptyline, pseudomonas UTI) Black  Hemoglobinuria, ochronosis—alkaptonuria (due to excretion of homogentisic acid) Purple:  Urinary tract infections in chronically catheterized pts, with alkaline urine

Red or Brown Urine Common causes are hemoglobin (either free or contained in RBCs) and myoglobin  All will be heme positive on dipstick Centrifugation of the urine differentiates whether the pigment is:  Contained within cells (hematuria) or represents hemoglobinuria or myoglobinuria Heme negative red urine  certain drugs, food dyes, and abnormal metabolites

Red to Brown Urine: Heme-Neg Dipstick Medications:  Doxorubicin, Chloroquine, Deferoxamine, Ibuprofen, Iron sorbitol, Nitrofurantoin, Phenazopyridine, Phenolphthalein, Rifampin Food dyes:  Beets, Blackberries, Food coloring Metabolites:  Bile pigments, Homogentisic acid, Melanin,  Methemoglobin, Porphyrin, Tyrosinosis, Urates (pink and turbid)

Specific Gravity (SG) SG is the ratio of urine density compared to a water standard  Sp gravity = mass of U vol /mass of equivalent dH2O vol SG indirectly measures renal concentrating ability Normal range Is measured by dipstick or refractometer

Specific Gravity – Falsely Elevated Excretion of radiopaque contrast media Excessive proteinuria (as in nephrosis or diabetes) Excessive glycosuria Refrigerated urine

Diagnostic Clues From Urine Odor Volatile acids responsible for normal urine odor Specific odors & diagnoses:  Acetone: Diabetic Ketoacidosis (DKA)  Ammonia : Infection with urea breakdown  Maple Syrup Urine Disease  Asparagus or garlic ingestion

Causes of Increased Turbidity Urate crystals in acid urine Phosphates in alkaline urine RBC's WBC's Bacteria Vaginal secretions Fat globules

Urine pH Range ; normal = 6 Animal protein diet : acid urine Vegetable / fruit diet : alkaline urine Stones that develop in acid urine:  Uric acid  Cysteine  Calcium oxalate Stones that develop in alkaline urine:  Calcium phosphate  Calcium carbonate  Mg PO4

Protein Analysis Normal urine contains small amounts of albumin & globulin Proteinuria exists if > 20 mg/dl  Incidence 6 to 9 % in asymptomatic patients Dipstick tests use tetrabromophenol blue indicator system (yellow to green as concentration ↑ ) React mainly with albumin False positive with quaternary ammonia compounds & phenazopyridine dyes

Sulfosalicylic Acid Test (SSA) SSA detects all proteins in the urine The acid denatures existing proteins and causes them to come out of solution  ↑ turbidity  Useful for detecting immunoglobulin light chains (multiple myeloma), especially where the albumin dipstick is negative or trace  Radio-contrast agents can cause false positive results, as can any substance precipitated by acid (cephalosporins, penicillins, sulfonamides)

Glucose Analysis Based on reduction of metal ions by glucose False positive reactions due to :  Hypochlorite or chlorine  Other sugars (galactose, lactose, fructose, maltose, as during pregnancy) Enzyme - based tests (glucose oxidase) are more specific for glucose Can have false negative results with ascorbic acid, tetracycline, or high uric acid

Reading Glucose mg/dl Negative0 Trace >2000 Correlation of Urine Glucose Readings

Hemoglobin Analysis Dipsticks for hemoglobin can detect 1-2 RBC per hpf  Detects heme protein: both hemoglobin and myoglobin Uses pseudoperoxodase activity of Hgb to oxidize a chromogen Free Hgb gives uniform color; intact RBC give a speckled pattern  False positive results can occur with alkaline urine, contamination with oxidizing agents, presence of semen

Ketones Choices are: Acetest, test tube, dipstick All use reaction between acetoacetic acid & nitroprusside to make a violet dye complex Acetone reaction is < 5 % of color change Beta-hydroxybutyrate not detected

Causes of False Positive Ketones Levodopa Phenolphthalein (in laxatives) Insulin Pyridium (phenazopyridine) Phenformin Phenylketonuria

Nitrate Analysis Nitrites are absent from normal urine Most UTI bacteria reduce urinary nitrates to nitrites Dipstick uses aromatic amine & diazonium compound to produce pink color in presence of nitrite False negatives :  High urine flow (dilutional) ; Frequent or continuous (foley) voiding  Ascorbic acid  Bacterial inhibition with antibiotics

Leukocyte Analysis Any purple color on dipstick indicates > 5 WBC's/hpf Detects intact & lysed WBC's + WBC casts False negatives :  Cephalexin, gentamicin, nitrofurantoin Up to 97 % sensitivity & 90 % specificity for culture - proven UTI's

Bacterial Counts < 1000 colonies per/ml implies only contamination Counts > 1000 and < 100,000 per/ml may imply infection Counts > 100,000 / ml imply infection

Cellular Casts Represents contents of renal tubules discharged into urine Cast types & associated diseases :  Broad, epithelial, fatty, granular, or waxy : parenchymal renal disease  RBC : acute glomerulonephritis  WBC : pyelonephritis

Cellular Casts RBC casts  Usually represent significant glomerular disease  Can occur after very strenuous exercise Hyaline casts  Clear, colorless ; due to protein precipitation  Occurrence depends on urine flow, pH, degree of proteinuria Granular casts  Result from disintegration of cell material into particles  Form waxy casts when renal failure is advanced

Urinary Crystals Normal crystals in acid pH: amorphous urates, uric acid, calcium oxalate, sodium urate, hippuric acid Normal crystals in alkaline pH: amorphous phosphate, triple phosphate, calcium phosphate, ammonium biurate, calcium carbonate Abnormal crystals in urine found in acid pH: cystine, cholesterol, tyrosine, leucine, billirubin

Urine Electrolytes Clinical situations where measurements useful :  Sodium  Volume depletion, acute oliguria, hyponatremia (R/O SIADH)  Chloride  Determine if metabolic alkalosis is chloride resistant or sensitive  Potassium  Determine site of K+ loss in hypokalemia (if < 10 meq/liter, implies GI tract as source)

Urine Culture All children (age < 14) and all males Women with history of :  Immunocompromised  Renal abnormalities  Diabetes mellitus  Recent instrumentation and indwelling catheter  Prolonged Symptoms before seeking care  3 or more ( ? > 5 ) UTI's in last year  Recent pyelonephritis  Recent hospitalization

Renal Function Tests

Physiology of Creatinine Is the breakdown product of creatine (the storage source for high-energy phosphate in muscle cells) CPK acts to add high energy phosphate to creatine from ATP Creatine-phosphate transfers the phosphate to re-make ATP when energy is needed for metabolism