Microscopic Examination of Urine Crystals and Casts PDF

Microscopic Examination of Urine- Crystals and Casts URINALYSIS & BODY FLUIDS by STRASINGER, S. & DI LORENZO, M. 7TH ED. - CHAPTER 7  Crystals Not usually found in freshly voided urine Many have little significance Significant ones: From metabolic disorders (cys...

Microscopic Examination of Urine- Crystals and Casts URINALYSIS & BODY FLUIDS by STRASINGER, S. & DI LORENZO, M. 7TH ED. - CHAPTER 7  Crystals Not usually found in freshly voided urine Many have little significance Significant ones: From metabolic disorders (cystine, tyrosine) Stone formation Medication regulation Identified by: Appearance pH of urine important Solubility characteristics  Urinary Crystals Most are not clinically significant Some labs report all crystals; others only report the clinically significant ones Appear as true geometrically formed structures or as amorphous material Must differentiate the few abnormal crystals indicating liver disease, inborn errors of metabolism, and damage to tubules Report Few according (1+) to your laboratory’s policies Positive OR Some (2+) Negative Many (3+) Marked (4+)  Crystal Formation Crystals are formed by precipitation of urine solutes: salts, organic compounds, and medications Formation is based on temperature, solute concentration, and pH Many crystals form in refrigerated specimens If crystals are found in freshly voided urine, they are usually associated with concentrated (high specific gravity) specimens.  General Identification Techniques Most have characteristic shapes and colors Most valuable aid to identification is urine pH Classification: normal acid, normal alkaline, abnormal acid All abnormal crystals are found in acid urine Polarized microscopy and solubility characteristics are also valuable in identification  Normal Crystals in Acid Urine Uric Acid Amorphous Urates  Uric Acid Crystals Shapes include: rhombic, four-sided flat plates (whetstones), wedges and rosettes Color: Yellow-brown Can occasionally be colorless and six-sided Similar to cystine crystals Highly birefringent under polarized light Cystine crystals are not Increased levels of uric acid crystals associated with: Increased purine and nucleic acid levels Leukemia patients receiving chemotherapy Patients with gout  Amorphorus Urates Shape: Granular sediment Color: Yellow-Brown or Pink (due to the pigment uroerythrin) Found in acidic urine with pH greater than 5.5 Can obscure the microscopic field and make it difficult to see other elements Common in refrigerated specimens. May dissolve if warmed. Normal Crystals in Acid/Neutral Urine Calcium Oxalate  Calcium Oxalate Crystals Shape: Two possible forms Most common – Dihydrate Calcium Oxalate Envelope-shaped Monohydrate Calcium Oxalate Oval or Dumbbell Color: Colorless Birefringent under polarized light Increased levels associated with: Renal Calculi Oxalate-Rich Foods Tomatoes, asparagus, spinach, oranges Ethylene Glycol Poisoning Noticeable presence of the  Normal Crystals in Alkaline Urine Amorphous Ammonium Biurate Phosphates Calcium Carbonate Calcium Phosphate Triple Phosphate  Amorphous Phosphates Shape: Granular sediment Color: White-colorless Present in large quantities after refrigeration Do not dissolve when warmed How do you differentiate between amorphous urates and amorphous phosphates? pH Color Urates Acid Pink Phosphates Alkaline White  Calcium Phosphate Shape: Flat rectangular plates or rosettes Color: Colorless Can be confused with sulfonamide crystals Use acetic acid to differentiate Calcium phosphate crystals will dissolve, Sulfonamide crystals do not. No clinical significance  Triple Phosphate (Ammonium Magnesium Phosphate) Shape: “coffin-lid” prism or fern leaf shaped Color: Colorless Birefringent under polarized light. No clinical significance Found in highly alkaline urine and patients with UTIs Due to the presence of urea-splitting bacteria  Ammonium Biurate Shape: Spicule-covered spheres, “thorny apples” Color: Yellow-brown Dissolve at 60OC Convert to uric acid crystals when glacial acetic acid is added Occur in old specimens Associated with the presence of ammonia produced by urea- splitting bacteria  Calcium Carbonate Shape: Small dumbbell or spherical Color: Colorless Can be confused with: Bacteria Calcium carbonate is birefringent but bacteria is not Amorphous material Gas is formed after the addition of acetic acid to calcium carbonate but not after addition to amorphous material No clinical significance  Abnormal Crystals Always in acidic urine or rarely in neutral urine. If abnormal crystals are suspected, confirm with chemical testing before reporting (if applicable) Check patient history, including disorders and medications to correlate your findings Sulfa drugs, Ampicillin can crystallize out in concentrated specimens  Abnormal Crystals Cystine - Metabolic disorder Cholesterol - Nephrotic syndrome Leucine Tyrosine - Liver diseases Bilirubin Sulfonamides Radiographic Dye - Medications Ampicillin  Cystine Shape: Hexagonal plates (thick or thin) Color: Colorless Difficult to differentiate from uric acid crystals Uric acid crystals are highly birefringent whereas only thick cystine crystals polarize. Confirmation can be made using the cyanide- nitroprusside test Found in cystinuria Metabolic disorder that prevents the reabsorption of cysteine by the renal tubules These patients tend to form renal stones at an early age  Cholesterol Shape: rectangular plates with notched corners Color: colorless Highly birefringent Associated with disorders that produce lipiduria Nephrotic Syndrome Will also see fatty casts and oval fat bodies  Liver Disease Crystals Leucine Tyrosine Bilirubin  Leucine Shape: Spheres with concentric circles and radial striations Color: Yellow-brown Seen less frequently than tyrosine crystals When present, should be accompanied by tyrosine crystals  Tyrosine Shape: Fine needles in clumps or rosettes Color: Colorless to Yellow Seen in conjunction with leucine crystals Chemical test for bilirubin will be positive. Also seen in inherited disorders of amino acid metabolism  Bilirubin Shape: Clumped needles or granules Color: Yellow Positive reagent strip for bilirubin Seen in disorders that produce renal tubular damage Ex. Viral hepatitis  Medication/Dye Crystals Sulfonamides Radiographic Dye Ampicillin  Sulfonamides Shape: Variety - needles, rhombics, whetstones, sheaves of wheat, rosettes Color: Varies - colorless to yellow-brown The variety of shapes and colors are due to the variety of sulfonamide medications available Inadequate patient hydration is the primary cause of sulfonamide crystallization. If seen in a fresh urine - can suggest possibility of tubular damage if crystals are  Radiographic Dye Shape: Flat plates (similar to cholesterol crystals) Color: Colorless Highly birefringent Differentiation from cholesterol crystals: Cholesterol crystals should be accompanied by lipid elements and protein Radiographic dye will give a very high specific gravity when measured with a refractometer Found in patients after they have had an I.V. injection of radiographic contrast media for x-ray studies.  Ampicillin Shape: Needles which form bundles after refrigeration Color: Colorless Found in patients following large doses of ampicillin who are not adequately hydrated.  Urinary Casts The major constituent of casts is uromodulin (Tamm-Horsfall protein) Uromodulin is excreted at a constant rate under normal conditions. The rate of excretion increases during stress and exercise. Uromodulin gels more readily under conditions of urine-flow stasis, acidity, and the presence of sodium and calcium. The size and shape of the cast depends on the tubule where it was formed. The cast matrix may become embedded with cells, bacteria, granules, pigments and crystals from the tubular filtrate.  Urinary Casts Shape: Cylindrical Parallel sides, rounded edges May contain inclusions from the tubular filtrate Cells, granules, pigments, etc. Casts DO NOT have dark edges Find casts under low power and identify under high power Low light is essential - casts have a low refractive index Report the number of casts seen/lpf  Urinary Casts - Composition and Formation Uromodulin is secreted by renal tubular epithelial cells of the distal convoluted tubule and collecting ducts. Secretion is increased during stress and exercise The formation of a matrix occurs from protein fibrils Occurs during urine stasis, acid pH, and presence of Na and Ca Uromodulin is not detected by reagent strips An increase in protein is due to albumin and underlying renal conditions An increase in urinary casts is called cylindruria.  Types of Urinary Casts Casts are classified based on their appearance and inclusions: Hyaline Red Blood Cell White Blood Cell Epithelial Cell Fatty Granular Waxy Broad  Hyaline Casts Most frequently seen cast Made up entirely of uromodulin Refractive index similar to that of urine Easy to overlook if not using low light Cylindrical with parallel sides and rounded ends Aging casts may have wrinkled or convoluted shapes Occasionally will have a cell or granule adhering to the matrix, but it is still  Hyaline Casts - Clinical Significance Normal: 0-2/lpf Non-pathological: Following strenuous exercise dehydration heat exposure stress Increased in: Acute glomerulonephritis Pyelonephritis Chronic renal disease Congestive heart failure  RBC Casts Orange-red color Cast matrix contain RBCs Confirmation: Free RBCs also in urine sediment Positive reagent strip test for blood Sources of error: Red cell clumps Only casts will have a matrix; clumps will not Reported as number of RBC casts/lpf  RBC Casts - Clinical Significance Bleeding within the nephron Primarily Glomerulonephritis Damage to the glomerulus allows RBCs to pass through the glomerular membrane Also seen with RBC casts associated with glomerular damage: Proteinuria Dysmorphic RBCs If intact RBCs are seen inside matrix = RBC cast Yeas t If RBC cast has degenerated due to stasis in the renal RBC  RBC Casts - Granular, Dirty, Brown Cast Clinical Significance Hemoglobin degradation products Associated with Acute Tubular Necrosis Caused by toxic effects of massive hemoglobinuria Can lead to renal failure Seen in conjunction with: RTE cells Positive reagent strip test for blood  WBC Casts Composed of neutrophils and may appear granular Multilobed nuclei will be present unless the cast has started to disintegrate. Supravital staining can be helpful in seeing the nuclei Confirmation: Free WBCs in the urine sediment Positive leukocyte esterase on the reagent strip Sources of error: White cell clumps can be mistaken as WBC casts  WBC Casts - Clinical Significance WBC casts indication inflammation/infection in the upper urinary tract (i.e. nephron) Primarily associated with pyelonephritis (upper UTI) Accompanied by RTE casts Not seen in cystitis (lower UTI) Present in acute interstitial nephritis (non- bacterial) May accompany RBC casts in glomerulonephritis  Renal Tubular Epithelial (RTE) Casts Represent advanced tubular destruction Associated with: Heavy metal, chemical or drug-induced toxicity Viral infections Allograft rejection Can accompany WBC casts in pyelonephritis Sources of error: Mistaken for WBC casts Use stain or phase microscopy to enhance nuclear detail  Granular Casts Occur as a result of disintegrating cellular casts Start off as course granules but will appear as fine granules if there is prolonged urinary stasis Allows the casts to remain in the tubules which gives them time to disintegrate If granular casts remain in the tubules for extended periods of time, the granules continue to disintegrate and the cast develops a waxy appearance. Clinical significance: Glomerulonephritis  Waxy Casts Brittle and highly refractive Appear fragmented with jagged ends and notches Easily visualized with stain Occur when hyaline and granular casts degenerate due to extreme urine stasis Clinical Significance: Extreme urine stasis Chronic renal failure  Broad Casts Wide casts Their presence indicates destruction and widening of the tubular walls Represent extreme urine stasis Any type of cast can occur as a broad form but the most common are granular and waxy. Also called Renal Failure Casts Bile-stained broad, waxy cast  Fatty Casts Will have fat droplets and oval fat bodies attached to the protein matrix Adherence Highly refractile under bright-field of fat droplets to microscopy cast matrix Confirmation is done by: Polarized microscopy Cholesterol will have maltese cross Sudan III or Oil Red O stains Triglycerides will stain orange Free fat droplets and oval fat bodies should be seen in the urine sediment as well.  Fatty Casts - Clinical Significance Primarily Nephrotic Syndrome A collection of symptoms that indicate kidney damage and include excess levels of protein in the urine. Also seen in: Tubular necrosis Diabetes Mellitus Crush injuries Fatty cast under phase microscopy  Oval Fat Bodies Lipid-containing RTE cells RTE cells absorb lipids in the glomerular filtrate (cholesterol, triglycerides or neutral fat) Cholesterol - will have maltese cross appearance under polarized light Triglycerides and neutral fats can be stained orange with Sudan III or Oil Red O  Criteria for Microscopics Laboratories will have specific criteria on when to perform a microscopic examination of urine sediment. Generally a microscopic is performed if any of the following reagent strip results are positive: Blood Leukocyte esterase Protein Nitrite If all reagent strip results are negative or normal, no microscopic examination is performed.  Urine Microscopy Setup Turn down light Scan edges of slide to Close Iris diaphragm almost fully look for casts, particularly if dipstick is Lower condenser positive for protein Focus first under low (10x) power ID under high dry (40x) Examine a minimum of 10 fields Report according to Reporting Increments Reporting Form Examine a minimum of 10 fields Casts are reported per lpf Cells are reported per hpf Reporting for bacteria and crystals may differ with each lab.  Correlating Results Microscopic Physical Chemical Elements RBCs Turbidity + Blood Red color + Protein WBCs Turbidity + Protein + Nitrite + LE Epithelial cells Turbidity Casts + Protein Bacteria Turbidity pH + Nitrite + Leukocytes Crystals Turbidity pH Color + Bilirubin