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Urine analysis
- 1. By Dr. KrishnaGharti Intern MBBS
- 2. Urinalysis isone of the most commonly used diagnostic tests in modern medicine. The urinalysis is an informative and noninvasive diagnostic tool that is readily accessible to the clinician in both the ambulatory and hospital settings. Hippocrates wrote about urine examination as early as 400 BC and correctly identified urine as a filtrate of blood. The modern era of reagent strip, or dipstick testing, began in 1956 and has constantly improved since then. Introduction
- 3. In apatient with evidence of kidney disease, such as someone with albuminuria or an acute or chronic reduction in the glomerular filtration rate. In a patient with suspected kidney disease. Kidney disease may be suspected on the basis of clinical findings (eg, edema) or because of a concurrent illness or condition that is commonly associated with kidney disease (eg, systemic lupus erythematosus, small-vessel vasculitis, newly identified hypertension). In an otherwise asymptomatic patient in order to clarify the significance of incidental findings noted on urine dipstick analyses (eg, microscopic hematuria) when the dipstick was part of a workup for another condition (eg, hypertension, diabetes mellitus). When to perform
- 4. In conjunctionwith the history, physical examination, and serum chemistries, the urinalysis plays a central role in evaluating acute and chronic kidney disease. In addition, abnormal findings on a routine urinalysis, even in an otherwise asymptomatic patient, may be the first evidence of underlying kidney disease. The urinalysis can also be used in some patients to monitor the course of established kidney disease Role in kidney disease
- 5. Methods of specimencollection Random sample: Sample which is collected anytime during the day. First voided specimen: Sample also referred to as a first morning specimen. A first voided specimen is the most concentrated and is the preferred specimen for pregnancy testing, bacterial cultures and microscopic examinations. Timed specimens: These specimens are used when the physician requires urine samples to be taken at specific intervals during the day. Twenty-four (24) hour urine specimens are required for creatinine clearance tests and many other hormone studies. Clean-catch midstream specimen: This sample type is collected if the urine is going to be cultured and examined for bacterial growth or used for cytology. Specimen collection
- 6. Catheterized specimen(CSU): These specimens are obtained by inserting a catheter or sterile flexible tube into the bladder via the urethra to withdraw urine. This procedure is done only by specially trained personnel Suprapubic Aspiration Specimen: This method is used when a bedridden patient cannot be catheterized or a sterile specimen is required. The urine specimen is collected by needle aspiration through the abdominal wall into the bladder. Pediatric Specimen: For infants and small children, a special urine collection bag is adhered to the skin surrounding the urethral area. Once the collection is completed, the urine is poured into a collection cup or transferred directly into an evacuated tube with a transfer straw.
- 7. Following collection,improper specimen handling can affect urinalysis results. The chemical composition of urine is relatively stable over 24 h if bacterial growth is inhibited. This can be accomplished by storing the sample at 2 to 8°C with minimal exposure to light. Samples should not be kept at room temperature for longer than 2 hours. Because formed elements are particularly unstable. In laboratory, samples more than 4 h old will not undergo microscopy for this reason. Specimens older than 24 h should not be used for urinalysis Storage
- 8. Gross evaluation Dipstick analysis Microscopicexamination of the urine sediment Components
- 9. Colour Normal: Yellow(light/pale to dark/deep amber) Other abnormal colour of urine Colour Causes Red Blood, Hb, Myoglobin, Drugs: Rifampicin, or phenytoin Food dyes, ingestion of beets, acute intermittent prophyria White Polyuria, phosphate crystals, chyluria, propofol Pink Uric acid crystals Black Alkaptonuria, Hb, onchronosis Green Methylen blue Purple Bacteriuria in catheter Gross evaluation
- 10. Turbidity Normal: Clear Turbidurine may be seen in the setting of infection, or as a result of precipitated crystals or chyluria Odour Normal: Aromatic Abnormal odours Odour Causes Ammonia like Urea splitting organisms Foul, offensive Old specimen, pus or inflammation Sweet Glucose Fruity Ketone Maple syrup like Maple syrup urine disease
- 11. The urinedipstick provides a rapid semi- quantitative assessment of urinary characteristics on a series of test pads embedded on a reagent strip. Most dipsticks permit the analysis of the following core urine parameters: heme, leukocyte esterase, nitrite, albumin, hydrogen ions, specific gravity, and glucose. Some dipsticks include test pads for additional parameters including urobilinogen and ketones. Dipstick analysis
- 12. Protein • Normallyprotein is absent in the urine. Albumin, globulins, and other large molecular weight protein cannot cross glomerular wall. Small proteins (<20 kDa) are freely filtered but readily reabsorbed by tubules. •The urine dipstick test for protein is most sensitive to albumin and provides a semi-quantitative means of assessing albuminuria. •The dipstick is insensitive to non-albumin proteins, most notably potentially nephrotoxic immunoglobulin light chains. A screen for the presence of such proteins may be performed with the sulfosalicylic acid (SSA) or trichlroacetic acid test. •Albumin level 30-300 mg/day is called micro-albuminiuria and albumin > 300 mg/day is called macroalbuminuria. • Categories of albuminuria: Grade Albumin level in urine (mg/day) Negative <10 Trace 15-30 1+ 30-100 2+ 100-300 3+ 300-1000 4+ >1000 Dipstick analysis
- 13. Causes ofproteinuria
- 14. Glucose Presenceof glucose in urine is called glycosuria. In patients with normal kidney function, significant glycosuria does not generally occur until the plasma glucose concentration exceeds 180 mg/dL. Causes of glycosuria • Diabetes mellitus • Pregnancy • Renal tubular acidosis • Drugs: corticosteroids
- 15. Blood Presenceof blood in the urine is known as hematuria. In dipstick test, heme is detected by chromogen strip. Positive dipstick for heme may result not only from urinary RBCs but also from hemoglobin or free myoglobin. Causes of hematuria
- 16. pH • pHis measurement of H+ ion concentration. pH of urine indicates acidification of urine. • The urine pH ranges from 4.5 to 8, depending upon the systemic acid-base balance. • Causes of change in urinary pH High pH Low pH Infection with urea splitting organisms respiratory and metabolic acidosis Renal tubular acidosis (type I and II) Uric acid calculi Vegetarian diet, diuretic therapy, vomiting, gastric suction and alkali therapy
- 17. Specific gravity •The osmolality of the urine can be inferred by measuring the urine specific gravity, which is defined as the weight of the solution compared with the weight of an equal volume of distilled water. • The urine specific gravity generally varies with the osmolality, rising by approximately 0.001 for every 35 to 40 mosmol/kg increase in urine osmolality. • Thus, a urine osmolality of 280 mosmol/kg (which is isosmotic to normal plasma) is usually associated with a urine specific gravity of 1.008 or 1.009. • Normal range: 1.003 – 1.030.
- 18. Nitrite • ManyEnterobacteriaceae species, the most common microorganisms causing urinary tract infections, elaborate the enzyme nitrate reductase, which confers the ability to convert urinary nitrate to nitrite. Thus, nitrite-positive urine may indicate underlying bacteriuria. • However, bacteriuria or frank infection may still be present in the absence of nitrite positivity. This would occur with organisms expressing low levels of nitrate reductase (eg, enterococcus), or when urine dwell time in the bladder is short. Leukocyte esterase • Leukocyte esterase released by lysed neutrophils and macrophages is a marker for the presence of white blood cells (WBCs). • However, a concentrated urine may impede cell lysis and therefore produce a false-negative result. • Proteinuria and glucosuria may also lead to a false-negative test for leukocyte esterase.
- 19. Urobilinogen Normallypresent in the urine in small quantity. Less than 1% of urobilinogen is passed by the kidneys the remainder is excreted in the faeces or transported back to the liver and converted into bile. Raised levels may be due to: • Cirrhosis • Hepatitis • Hepatic necrosis • Haemolytic and pernicious anaemia • Malaria
- 20. Ketone bodies Not normally found in the urine, ketones are produced during fat metabolism. Presence of ketones may indicate: • Diabetes • Alcoholism • Eclampsia • A state of starvation • Pregnancy
- 21. Microscopic examinationof the urine sediment is an essential part of the urinalysis, as it enables confirmation and clarification of urine dipstick findings and also the identification of structures that are not evaluated by the urine dipstick (eg, epithelial cells, casts, crystals). To perform the urine sediment examination, 10 mL of urine is centrifuged at 3000 rpm for five minutes. Most of the supernatant is then poured out, and the pellet is resuspended with gentle shaking of the tube. A pipette can then be used to place approximately 50 microL (or a small drop) of resuspended sediment on a glass slide, followed by application of a coverslip. A brightfield (or if available, phase-contrast) microscope with a binocular head, built-in light source, and polarizing filters should be used. The entire specimen is initially scanned at low power (100x) with particular attention to the edges of the coverslip where casts tend to migrate. High power (400x) should then be used to better characterize structures that were identified at lower power. Microscopic examination
- 22. Red cells •Hematuria may be grossly visible or microscopic. Microscopic hematuria is commonly defined as the presence of two to five RBCs per high- powered field in a urine sediment. • Causes of gross hematuria Renal stones Tuberculosis Trauma Prostatitis • Hematuria may be transient or persistent. Transient hematuria is relatively common in young patients and may occur following exercise or sexual intercourse. • Causes of transient hematuria Menstruation , mild trauma, viral infections Urinary tract infection (cystitis or prostatitis)
- 23. • Persistent hematuria(>3 RBC/hpf on three urinalysis or single urinalysis with >100 RBCs or gross hematuria) should always be evaluated. • Causes of persistent hematuria Kidney stones Malignancy Glomerular disease • Distinguishing between glomerular and non-glomerular causes is the first key step in the evaluation of unexplained hematuria. • Isomorphic RBCs have an appearance similar to erythrocytes in the circulation (small, anucleated cells shaped as biconcave discs) and can be seen with any cause of hematuria. • By contrast, dysmorphic RBCs (which have an altered morphology) are suggestive of glomerular disease
- 24. White cells •Although the entire spectrum of WBCs may be seen in the urine, neutrophils and eosinophils are the cell types of greatest practical interest. • Urinary neutrophils are commonly associated with bacteriuria. However, if the corresponding urine culture is negative (ie, sterile pyuria), interstitial nephritis, renal tuberculosis, and nephrolithiasis should be considered. • Urine eosinophils can be detected by applying Wright's or Hansel's stain to the urine sediment. The presence of eosinophiluria has classically been considered a marker of acute interstitial nephritis.
- 25. Epithelial cells •Epithelial cells may appear in the urine after being shed from anywhere within the genitourinary tract. • Renal tubular cells are 1.5 to 3 times larger than white cells and are further distinguished by a round, large, centrally- located nucleus. • Transitional epithelial cells originate anywhere from the renal pelvis to the proximal urethra and are slightly larger than renal tubular epithelial cells. They may have a pear-like or oval appearance. • Squamous epithelial cells are derived from the distal urethra or external genitalia. They are large and irregular in shape with a small central nucleus, and their presence represents contamination by genital secretions.
- 26. Casts • Castsare cylindrical structures that are formed in the tubular lumen; several factors favor cast formation: urine stasis, low pH, and greater urinary concentration. • Casts will assume the shape and size of the renal tubule in which they are formed. All casts have an organic matrix composed primarily of Tamm-Horsfall mucoprotein, which comprises the basic architecture for any cast. • Casts are defined by the nature of the cells or other elements that are embedded in the cast matrix. • The observation of cells within a cast is highly significant since their presence is diagnostic of an intrarenal origin. • Different types of cast with their causes: Casts Causes RBC casts Proliferative glumerulonephritis WBC casts Interstitial inflamation Renal tubular epithelial casts Acute tubular nephritis, acute interstitial nephritis Granular casts ATN →AKI Hyaline casts Concentrated urine, diuretic therapy Waxy casts Nonspecific may be present in Acute and chronic kidney disease Broad casts Advanced CKD
- 27. Crystals • Whethercrystals form in the urine depends upon a variety of factors, including the degree of concentration of constituent molecules, the urine pH, and the presence of inhibitors of crystallization. • Abnormal crystals with their cause Crystals Causes Uric acid Uric acid nephropathy Calcium oxalate or calcium phosphate Calcium oxalate stone Cystine Cystinuria Magnesium ammonium phosphate Infection with urea splitting organism AKI + calcium oxalate Ethylene glycol ingestion larger number of uric acid crystals + AKI Tumor lysis syndrome
- 28. Microorganism • Bacteriaare often seen in the urine, although the clinical significance of bacteriuria is generally guided by patient symptoms. • Significant bacteriuria is defined as a urine sample containing more than 105 colonies/ml of urine. • Fungi are also frequently present.
- 29. Harrison’s Principleof Internal Medicine 19th edition Davidson’s principle of internal medicine 22nd edition www.uptodate.com www.medscape.com References
- 30.
Editor's Notes
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