Urine Examination

Examination of the urine considered a routine extension of the physical examination in all patients.

Appearance

  • Cloudy urine may result from high concentrations of leucocytes, epithelial cells, or bacteria.
  • The appearance of the urine that may assist diagnosis at an early stage.
  • Blood causes a pink to black discoloration, depending on the number of RBCs
  • Jaundice may cause dark yellow or brown urine.
  • Haemoglobinuria and myoglobinuria causes of dark urine that tests +ve for blood on dipstick examination.
  • Normal urine tends to darken on standingOdour
  • Offensive urine usually denotes infection
  • Sweet urine suggests ketones.
  • Certain rare metabolic diseases confer characteristic smellsCauses of a coloured urine
  • Beetroot ingestion (red).
  • Blood (pink/red to brown/black).
  • Chloroquine (brown).
  • Chyluria (milky white).
  • Haemoglobin (pink/red to brown/black).
  • Hyperbilirubinaemia (yellow/brown).
  • Methylene blue
  • Myoglobin (pink/red to brown/black).
  • Nitrofurantoin (brown).
  • Onchronosis (black).
  • Phenytoin (red).
  • Propofol (green).
  • Rifampicin (orange).
  • Senna (orange).Specific gravityRefers to the weight of a solution, with respect to an equal weight of distilled water
  • normal range 1.003 – 1.035 in urineOsmolality
  • Refers to the solute concentration of a solution.
  • It cannot be measured with a dipstick.
  • Low Osmolality result from polyuriaUrinary pH
  • Urinary pH ranges from 4.5 to 8.0 usually 5.0 – 6.0
  • Most people pass acidic urine the majority of the time.Glucose
  • Glycosuria results when tubular reabsorptive capacity for glucose is exceeded >10mmol/L.
  • A valuable screening tool, but less useful for diagnosis and monitoring of DM.
  • Renal glycosuria occurs when proximal tubular injury leads to a failure to reabsorb filtered glucose .Protein
  • Urinary protein excretion should not exceed 150mg/day, of which less than 20mg is albumin.
  • The remainder consists mainly of non serum derived tubular mucoprotein, such as Tamm Horsfall
  • Increased excretion of albumin is a sensitive marker of renal, particularly glomerular, disease.
  • Protein excretion can be measured in untimed spot or timed (usually 24h) samples.Result;Estimated quantity;Trace0.15–0.3g/L+0.3g/L++1g/L+++2.5–5g/L++++>10g/LProteinuria
  • Normal: <30mg/g.
  • Microalbuminuria: 30 – 300mg/g.
  • Overt proteinuria: >300mg/g.Red blood cells
  • Haematuria is defined as the presence of two red blood cells per high-powered field in urine.
  • The amount determines whether it is visible to the naked eye
  • Hb induces a colour change usually green in a dye linked to organic peroxide.
  • Dipsticks detect as little as two RBCs per fiel
  • If a dipstick is +ve, it is still desirable to perform confirmatory microscopy.
  • Dipsticks detect Hb and it remain +ve, even after red blood cells lysis.
  • They detect haemoglobinuria from intravascular haemolysis
  • They detect myoglobin from muscle breakdown
  • Glomerular bleeding, Red blood cells that pass into the urine through aninflamed or damaged glomerulus may show budding, spiculation or other surface irregularitiesNeutrophils: are a prominent feature of urinary infection but may also be present in infl ammatory renal conditions.
  • Sterile pyuria refers to the situation wherein leucocytes are seen consistently on microscopy, but subsequent culture is sterile.* Causes of sterile pyuria
  • Partially treated urinary truct infection ,Calculi, Prostatitis, Bladder tumour, Papillary necrosis, Appendicitis.Lymphocytes: may be seen in prostatitis, cystitis.Microorganisms
  • Bacteriuria: normal urine is sterile. Simultaneous presence of leucocytes suggests true infection
  • Fungi: Candida species are most frequently encountered. May result from genital contamination.
  • Trichomonas: oval and fl agellate (motile if alive). Usually a genital contaminant.
  • Schistosoma haematobium: ova detection is an important technique in endemic areas.Urine culture: Culture and sensitivity differentiates contamination from true infection and guides treatment. A pure growth of >10 colony forming units /mL is the conventional diagnostic criterion for urinary tract infectionCasts: are plugs of Tamm– Horsfall mucoprotein within the renal tubules, with a characteristic cylindrical shape. They are classified according to appearance and the cellular elements embedded in them. Though produced in normal kidneys, they can be valuable clues to the presence of renal diseaseNon-cellular casts: Hyaline casts: mucoprotein alone and virtually transparent. A non specific finding that occurs in concentrated urine.Granular casts: granular material is embedded in the cast. Often pathological but non specific.Broad or waxy casts: hyaline material with a waxy appearance under the microscope. Form in dilated, poorly functioning tubules of advanced CKD.Cellular casts
  • Red cell casts: virtually diagnostic of GN.
  • White cell casts: characteristic of acute pyelonephritis may help to distinguish upper from lower tract infection. Also occur in TIN.
  • Epithelial cell casts: sloughed epithelial cells embedded in mucoprotein. A non-specific feature of ATN. Also found in GN.
  • Fatty casts: contain either lipid-fi lled tubular epithelial cells or free lipid globules. Distinguished from other casts by Maltese cross appearance under polarized light. Occur in the lipid-laden urine of the nephrotic syndrome. Lipids may also appear as droplets or crystals. When clumped, these are referred to as oval fat bodies .
  • Other casts: under the right conditions, any constituent of the urine (microorganisms, crystals, bilirubin, or myoglobin) may become entrapped in a mucoprotein cast.CrystalsDetected by examining the urine under polarized light Most crystals are clinically irrelevant. Uric acid. Usually lozenges with a yellow-brown hue. Precipitate at acid pH. A few may be normal as high meat intake, but quantities may indicate hyperuricosuria. May be present in acute urate nephropathyCalcium oxalateMay be monohydrated (ovoid) or bihydrated (pyramidal like the back of an envelope). Prefer an acidic pH but not always. A few may be normal(spinach and chocolate ingestion) but can denote hypercalciuria or hyperoxaluria. A diagnostic clue in ethylene glycol poisoning in both real life and examsCalcium phosphateHeterogeneous in their appearance (needles, prisms, stars). Favoured by alkaline pH. Might be a risk factor for calcium stone formation. Magnesium ammonium phosphate (triple phosphate CystineHexagonal Cystineis not a constituent of normal urine so always significant. Prefer acid urine. A marker of cystinuria Cholesterol Thin plates with sharp edges. Occur with heavy proteinuria.Drug-induced crystalluriaMany drugs can precipitate in the renal tubule. In severe cases this may cause AKI.
  • Antibiotics: sulfadiazine, amoxicillin.
  • Antiviral agents: aciclovir, valaciclovir, famciclovir, ganciclovir, valganciclovir, and indinavir.
  • Methotrexate.
  • Primidone (a barbiturate).
  • Triamterene.
  • Vitamin C (calcium oxalate deposition).

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