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Urinalysis
This document provides an overview of urinalysis, including reference values for various analytes, explanations of urine characteristics like color and odor, and descriptions of cells and casts that may be observed in urine microscopy. Key points include normal ranges for urine specific gravity, pH, glucose, proteins, and blood; how urine analyte tests work; causes of abnormal urine colors and odors; and clinical associations of different urine microscopy findings like types of casts and crystals. The goal of urinalysis is to screen for urinary tract infections and kidney diseases.
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Urinalysis
- 1. Urinalysis Christos Argyropoulos MD,PhD, FASN University of New Mexico School of Medicine
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- 3. Reference (“normal”) valuesin UA •Color – Yellow (light/pale to dark/deep amber) •Clarity/turbidity – Clear or cloudy •pH – 4.5-8 •Specific gravity – 1.005-1.025 •Glucose - ≤130 mg/d •Ketones – None •Nitrites – Negative •Leukocyte esterase – Negative •Bilirubin – Negative •Urobilirubin – Small amount (0.5-1 mg/dL) •Blood - ≤3 RBCs •Protein - ≤150 mg/d •RBCs - ≤2 RBCs/hpf •WBCs - ≤2-5 WBCs/hpf •Squamous epithelial cells - ≤15-20 squamous epithelial cells/hpf •Casts – 0-5 hyaline casts/lpf •Crystals – Occasionally •Bacteria – None •Yeast - None
- 4. Urine color Am FamPhysician. 2005 Mar 15;71(6):1153-1162.
- 5. Odor • Infection, themost common cause of abnormal urine odor • production of ammonia by bacteria. • Ketones may cause a fruity or sweet odor. • Other disease Associations • Maple syrup urine disease (maple syrup odor), • Phenylketonuria (mousy odor), • isovaleric acidemia (sweaty feet odor), • hypermethioninemia (fishy odor).
- 6. Urine pH • Detectedby a double indicator (methy red and bromthymo blue) to give a broad range of colors • When measured with electrodes, normal pH is 4.5 – 7.8 • Reagents strips should not be trusted outside the range of 5.5 – 7.5 • High upH (>7)may indicate either infection or overgrowth (prolonged storage) with urea-splitting organisms • Alkalic pH is seen with diuretics, vomiting, gastric suction and bicarbonate therapy • Acidic upH(<5) is commonly seen in systemic acidosis • upH> 5-5.5 in the setting of systemic acidosis →RTA
- 7. Measures of RelativeDensity: Specific Gravity • Determined by the number and size of particles in the urine • Reagent strip contains a polymer which is saturated with Hydrogen ions. These are displaced by urinary cations=>change in local pH – Glucose and Urea DO NOT affect reagent strip SG – Poor correlation between SG and Urine osmolality – SG is falsely high when UpH<6, falsely low when UpH>7 • Isosthenuria: fixed SG @ 1.010 – clue to CKD in real life and the boards
- 8. Measures of RelativeDensity: Urine Osmolality • Biomarker of ADH action on the distal tubule • Measured directly with an osmometer • Under regular conditions, one would expect each 35-40 mOsm/kg to increase SG by 0.001 • Proteinuria, mannitol, dextrans and radiographic contrast may affect osmolality • Used to investigate disorders of concentration and dilution (more to follow)
- 9. Bilirubin & Urobilinogen •Only conjugated bilirubin passes into the urine • Test for bilirubin will be positive in obstructive jaundice, but negative in hemolysis • Urine urobilinogen is often positive in hemolysis • None of them are great tests for liver disease despite the high analytic sensitivity of the reagent
- 10. Leukocyte Esterase andNitrates Leukocyte Esterase • Esterases are endoleukocyte enzymes released upon cell lysis • Colorimetric detection • False (+) when ↑ lysis (+LE w/o WBCs on microscopy) – ↑ storage, ↓ SG, ↓ UpH – Think about storage conditions when w/u bacteriuria Nitrates • Requires the presence of nitrate reducing bacteria • The strip actually detects nitrite not nitrate • Conversion of nitrate to nitrite requires at least 4 hours, so inadequate bladder retention can give false –ve results
- 11. Energy Substrate Metabolism Glucose •Highly sensitive test based on an oxidative reaction • Glucose is not normally present in the urine • Presence indicates that the plasma glucose is above the threshold of renal reabsorption (180-250 mg/dl) OR interference with this process: – Proximal tubulopathies (e.g. Fanconi s) – SGLT2 inhibitors Ketones • Acetoacetate and acetate detected with the nitroprusside reaction (reduction reaction) • Beta hydroxybutyrate is not detected via this reaction (and this is 80% of ketones in human ketotic states) • Urine ketones may be +ve when serum test is –ve (nowadays indicates starvation ketosis) – used in the 70s as part of self- monitoring for diabetes (much cheaper than glucometer strips) • Alcoholic KA and DKA will also give +ve urine tests
- 12. Heme group detection (hemoglobinand myoglobin) • Peroxidase type of reaction catalyzed by the heme moiety of either compound • High oxidative states (e.g. betadine) or bacteria with pseudoperoxidase activity (Eenterobacteriaciae, Staph, Strep) will cause +ve reactions • Normally haptoglobin binds both in serum • Large hemolysis/rhabdomyolysis will cause spillover in urine • Positive test in the absence of RBCs in microscopy suggest either rhabdo or hemolysis
- 13. False (+) andFalse Negative UA Am Fam Physician. 2005 Mar 15;71(6):1153-1162. If a compound is detected via an oxidative reaction, then oxidative agents will cause +ve, reductive agents (e.g. ascorbic acid) false –ve results and vice versa
- 14. URINE MICROSCOPY More thanmeets the eye http://dx.doi.org/10.1053/j.ajkd.2007.11.039 All images from Core Curriculum Nephrology 2008
- 15. Pre-analytic considerations • Elementswill deteriorate rapidly so fresh fresh urine (within 2-5 mins of collection) should be examined • A midstream specimen is preferred for examination • 5-12 ml , centrifuged at 400 g(2000 rpm) x 5 min, remove supernatant by suction, pellet resuspended and specimen examined under phase contrast
- 16. Cells of theUrine Sediment
- 17. Renal Causes ofHematuria
- 18. Non Renal Causesof Hematuria
- 19. Hematuria Algorithm Am FamPhysician. 2013 Dec 1;88(11):747-754
- 20. Hematuria and GUmalignancy Pretest probabilities Risk Factors for GU CA Am Fam Physician. 2013 Dec 1;88(11):747-754
- 21. Types and clinicalassociations of casts in urine microscopy
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- 23. Clinical Urine MicroscopyPatterns
- 24. Figure 1 American Journalof Kidney Diseases 2008 51, 1052-1067DOI: (10.1053/j.ajkd.2007.11.039) Copyright © 2008 National Kidney Foundation, Inc. Terms and Conditions Isomorphic RBCs Dysmorphic RBCs Acanthocytes Proximal tubular cells Glomerular hematuria: 10-80% dysmorphic RBCs or > 5% acanthocytes
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- 27. Figure 2 American Journalof Kidney Diseases 2008 51, 1052-1067DOI: (10.1053/j.ajkd.2007.11.039) Copyright © 2008 National Kidney Foundation, Inc. Terms and Conditions Oval fat bodies (lipiduria as in nephrotic syndrome)
- 28. Figure 3 American Journalof Kidney Diseases 2008 51, 1052-1067DOI: (10.1053/j.ajkd.2007.11.039) Copyright © 2008 National Kidney Foundation, Inc. Terms and Conditions Fine granular casts Waxy cast RBC cast Renal Tubular Epithelial cast
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- 30. Maltese cross (fattycast under polarized light) Fatty cast (bright-field microscopy)
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- 35. Figure 4 American Journalof Kidney Diseases 2008 51, 1052-1067DOI: (10.1053/j.ajkd.2007.11.039) Copyright © 2008 National Kidney Foundation, Inc. Terms and Conditions Cholesterol crystals Cystine (benzene shaped) crystals Amoxycillin Crystal Benzene Crystal