CHEM 110 - Clinical Chemistry 1 - LO3 PDF

Learning Outcome 3: Interpret microscopic urinalysis results and their correlation to clinical pathology. Learning Step 3.1: Describe preparation of urine sediment for microscopic urinalysis. 3.1.1 Reading Assignment Read the introductory paragraphs, Sediment Preparation and Microscopic Observation...

Learning Outcome 3: Interpret microscopic urinalysis results and their correlation to clinical pathology. Learning Step 3.1: Describe preparation of urine sediment for microscopic urinalysis. 3.1.1 Reading Assignment Read the introductory paragraphs, Sediment Preparation and Microscopic Observation and Enumeration pages 112-113 from the textbook, Mundt and Shanahan, Graff’s Textbook of Urinalysis and Body Fluids. 3rd Ed. Formatting 3.1.2 Instruction Sheet: Preparation of Urine Sediment Microscopic urinalysis may be done as requested by the physician or the laboratory may have a protocol to do microscopic analysis only on specimens that are cloudy and/or contain one of the following on chemical urinalysis: blood leukocytes nitrites protein Because consistency and standardization of microscopic examinations are important, there are various commercial systems available to laboratories to assist in the preparation of a urine sediment. Regardless of the system used, care must be taken that each step is followed consistently by all lab personnel to provide accurate results. Urine Volume Most systems use a 10-12 ml conical urine sample tube. If the specimen of less than the optimum volume is processed, according to general protocol a comment should be added to the microscopic report indicating that the evaluation was done on a smaller than normal volume. Some laboratories choose to do the microscopic urinalysis on an uncentrifuged specimen if the specimen volume is less than optimal. A comment would be added to the report that the microscopic analysis was done on an uncentrifuged specimen. Page 54 CHEM 110 – Clinical Chemistry 1 – LO3 Centrifugation When the chemical analyses have been completed, the conical tube is centrifuged at 400-450g (Relative Centrifugal Force) for 5 minutes. RCF(g) = 1.118 x 10-5 x radius in cm x (rpm)2 Centrifugation at 400-450g for 5 minutes will allow an adequate sediment to form without the disruption of the fragile formed elements. The supernatant is then removed from the sediment so that all sediment volumes are consistent. The sediment may or may not be stained before microscopic examination. Viewing the Sediment The urine sediment must be gently mixed to resuspend the particles and transferred to a standardized slide. Subdued light must be used to provide adequate contrast. This is obtained by closing the iris diaphragm located in the substage condenser. If too much light is used, some structures will be missed. The fine focus should be continuously adjusted while performing the microscopic examination. This ensures that objects on a different focal plane are counted and identified. Casts are counted on 10x but identified on 40x. Other microscopic elements are counted or observed on 40x. Scan a minimum of 10 fields. Final counts for casts and cells are an average of those fields. CHEM 110 - Clinical Chemistry 1 – LO3 Page 55 Learning Step 3.2: Describe the elements seen in microscopic urinalysis and correlate to clinical pathology. 3.2.1 Reading Assignment Read pages 113-136 from the textbook, Mundt and Shanahan, Graff’s Textbook of Urinalysis and Body Fluids. 3rd Ed. 3.2.2 Instruction Sheet: Microscopic Urinalysis Cells Three types of cells can be seen in urine sediment: red blood cells, leukocytes, and epithelial cells. Red Blood Cells In normal urine, the upper limit of normal is 2-5/HPF (high power field). An increased number of RBCs in urine is called hematuria. When increased red blood cells are accompanied by red blood cell casts, the source of the hematuria is probably renal. Increased red blood cells in the absence of red blood cell casts suggests the source of the hematuria is somewhere in the urinary tract other than the kidney. Page 56 CHEM 110 – Clinical Chemistry 1 – LO3 Depending on the osmotic pressure (OP) and the pH of the urine, the appearance of red cells can be altered. If the osmotic pressure is high, the RBCs will appear crenated; if the osmotic pressure is low or the pH very alkaline, the RBCs will be swollen or lysed. When lysing occurs, the microscopic examination may show the empty red blood cell membranes which are often referred to as “ghost cells” and are very difficult to see. Ghost red blood cells are still counted when performing microscopic urinalysis. At times, RBCs may be confused with WBCs, yeast, urate crystals, or atypical calcium oxalate. To help confirm the presence of RBCs, check the blood portion of the reagent strip: it should be positive if there are at least 5-10 RBC/HPF. Red blood cells may also be lysed with acetic acid to help with differentiation. Leukocytes In normal urine the upper limit is 5-8/HPF. Leukocytes probably enter the urine of healthy individuals by diapedesis through the glomerular membrane or the tubular cells. An increased number of leukocytes in urine is called pyuria. The most common type of leukocyte seen is the neutrophil which can sometimes be identified by the multilobed nucleus. Slight pyuria along with proteinuria, will occur in a healthy individual following strenuous exercise or stress. Hyaline or granular casts may also be observed. Pyuria is associated with an inflammatory process in or adjacent to the urinary tract. Leukocytes are attracted to any area of inflammation, and, because of their ameboid properties, they can penetrate the areas adjacent to the inflammatory site. Sometimes pyuria is seen in conditions such as appendicitis and pancreatitis. It is also found in non-infectious conditions such as glomerulonephritis, dehydration, fever, or irritation to the ureter, bladder, or urethra. Acute infection of the urinary tract is suggested when 50 or more leukocytes per HPF are seen in microscopic examination of urine sediment, especially when they occur in clumps. If this degree of pyuria is accompanied by minimal proteinuria and leukocyte casts, the probable cause is pyelonephritis. If accompanied by minimal proteinuria and no casts, it is likely an infection of the lower urinary tract. CHEM 110 - Clinical Chemistry 1 – LO3 Page 57 Leukocytes shrink if the urine is concentrated and swell up or are rapidly lysed in the urine is dilute or alkaline. Studies have shown the number of leukocytes decreases by 60% within two hours after collection if the urine is alkaline and dilute, and not refrigerated. When leukocytes swell in dilute urine, their granules may show Brownian movement. Cells which develop this characteristic are called “glitter cells”. Glitter cells are not reported. Leukocytes in urine sediment may be confused with RBCs or renal tubular epithelial cells (RTEs). leukocytes “lumpy nucleus” RTEs round central nucleus RBCs smaller, no nucleus To confirm the presence of Leukocytes, check the leukocyte portion of the reagent strip: it should be positive if there at least 10/HPF. Page 58 CHEM 110 – Clinical Chemistry 1 – LO3