Urinalysis Flashcards
Dipstick urine testing: pH
• Most acid = excreted as NH4
• Normal pH range: 4.5-8.0
o Dipstick less accurate for pH 7.5
o Narrower dipstick range than urine range
- High pH (>7) → infection with urea-splitting organism (proteus), vegetarian diet, diuretics, vomiting
- Low pH (<5) → acidemia, ingestion of large amount of meat (high protein), drugs (methenamine, fosfomycin)
Dipstick urine testing: blood/Hemoglobin
- Pseudoperoxidase activity
- Need to examine microscopic specimen
(+) dipstick test but (-) micro test → hemoglobin/myoglobin
o Free hemoglobin = intravascular hemolysis and hemoglobinuria
o Myoglobin = muscle damage
- False (+) = microbial peroxidase
- False (-) = Vitamin C
Dipstick urine testing: glucose
- Glucose oxidase/ peroxidase reaction
- Highly specific
- Detects glucose from 0.5 to 20 g/L
- False (-) = ascorbic acid, ketoacids, pyridium metabolites
Dipstick urine testing: Protein
- Highly sensitive to albumin (less to globulins, Hb, light chains)
- Other methods needed for accurate measurement of non-albumin proteins
- Need to note SPG to determine protein
Albuminuria: early indicator of kidney injury; prognostic
o Healthy adults: < 30 mg/ 1 g of Cr
o Microalbuminuria: 30-300 mg/ 1 g of Cr
o Macroalbuminuria: >300 mg/ 1 g of Cr
o Anything < 0.15 g/day • Nephrotic syndrome: >3.5 g/day o Spot urine protein in g/1g of creatinine in a random sample • Normal: 1g /1 g of Cr • Nephrotic syndrome: >3.5 g/1 g of Cr
• False (+) = alkaline urine, especially quaternary ammonium compounds (skin cleansers)
Negative: 0 mg/dL Trace: 15-30 1+: 30-100 2+: 100-300 3+: 300-1000 4+: >1000
Dipstick urine testing: urobilinogen/bilirubin
Urobilinogen: o False (+): contamination with stool, sulfonamides o False (-): degradation to urobilin
Conjugated bilirubin: o False (+): chlorpromazine/phenazopyridine/selenium o False (-): vitamin C
Both = little clinical use (not very sensitive to detect liver disease)
Dipstick urine testing: ketones
- Tests for acetoacetate and acetone
- Does NOT detect beta-hydroxybutyrate (often 80% of total serum ketones)
- Seen in starvation, diabetic ketoacidosis, AKA
- False (+): Vitamin C, phenazopyridine, levodopa, captopril, mesna
- False (-): standing or old urine
Dipstick urine testing: Leukocyte esterase
- Screens for WBCs by indoxyl esterase activity
- May detect WBCs despite micro being negative (ex: if WBCs broken down)
- False (+): rare but if formaldehyde is used as a preservative, contamination with vaginal debris
- False (-): high protein or glucose, tetracycline and cephalexin, high SPG, excess oxalate
Dipstick urine testing: Nitrites
- Detects bacteria that reduce nitrates to nitrites
* Does NOT detect: Pseudomonas, N. gonorrhoeae, Strep faecalis, Enterococcus, M. tuberculosis
Describe what microalbuminuria is, and explain the significance in a patient with diabetes mellitus
• Microalbuminuria: 30-300 mg/ 1 g of Cr
• In diabetes, persistent microabluminuria can lead to diabetic nephropathy
o If test negative for dipstick proteinuria → should then test for microalbuminuria
RBC in urine
• 7 micrometer uniform biconcave disks (monomorphic or isomorphic)
Dysmorphic:
• Spicules, blebs, vesicles
• Caused by RBC passing through GBM and then going through high tonicity of renal tubule
- 80% of hematuria = non-glomerular in origin (especially with normal RBC appearance)
- > 40% dysmorphic or 5% acanthocytes (specific type of dysmorphic RBCs) or RBC casts = glomerular hematuria
WBC in urine
- Neutrophils, Eosinophils, lymphocytes, macrophages
- WBCs (large, multilobed nuclei with granular cytoplasm) = UTI
- Eosinophils = allergic tubulointerstitial disease
- PMNs ~ 12 micrometers
- Indicates inflammation/infection
Explain the significance of the presence of different types of cells in urine
o Squamous Epithelial cells = genital contamination
o Transitional Epithelial cells = infection, neoplasia
o Renal Epithelial cells = inflammation, ATN
o Fat globules (epithelial cells filled with lipid) = nephrotic disease
• Appear like Maltese cross under polarized light
Hyaline casts
• Almost all Tamm-Horsfall protein
• Seen in normal individuals
• Translucent, ground-glass appearance
From ascending limb
Granular casts
- From precipitation of protein or disrupted cells in the hyaline matrix
- Can be fine-granular or coarse granular
- Non-specific, but usually pathologic
- Post exercise, volume depletion, ATN, GN, tubulointerstitial disease (types of chronic kidney diseases)
Muddy brown casts
- Coarse granular casts
- In AKI/ATN
- From renal tubular cells
RBC casts
- Hallmark for glomerulonephritis
- Indicates intraparenchymal bleeding
- Can be hard to distinguish from coarse granular casts, but usually found along with hematuria
WBC casts
- Characteristic of pyelonephritis
* Seen also with interstitial nephritis and tubulointerstitial disorders
Waxy/broad casts
- Hyaline material but higher refractive index → waxy appearance
- Have fissures along edges
- Form in dilated and atrophic tubules due to Chronic parenchymal disease
Calcium oxalate crystals
- Uniform, small, double pyramids
- Crosses in a square or dumbbell shaped
- Seen in ethylene glycol toxicity
Triple phosphate crystals
- Calcium magnesium ammonium pyrophosphate
- Coffin-lid appearance:
- Urea splitting organisms (ex: proteus)
Urate crystals
- Rhomboid (no cross in middle) or needle-shaped
* Seen in gout
Cystine Crystals
- Hexagonal
- Seen in cystinuria
- Common cause of kidney stones in children
Indinavir crystals
(HIV medication = protease inhibitor)
• Fan or starburst pattern
Urine fat/lipids
o Almost always pathologic
o Seen in nephrotic syndrome, fat embolization syndrome
o Free droplets or oval fat bodies
o Cholesterol esters: anisotropic (appear as Maltese Crosses under polarized light)
o Triglycerides: isotropic
o False (+) = some crystals, starch granules, mineral oil
Micro-organisms in urine
o Fungal = budding yeast
o Trichomonas = flagellate organisms
o S. haematobium
Correlate urinary abnormalities with some common kidney diseases: color
o Hematuria/hemoglobinuria = red/pink o Liver failure = jaundice o Chyluria = white/milky o Infection o Drugs: rifampin = orange; Phenytoin = red o Foods: beets, senna, rhubarb, carotene
Correlate urinary abnormalities with some common kidney diseases: turbidity
o Normally = clear
o Abnormal = UTI, hematuria, genital contamination
Correlate urinary abnormalities with some common kidney diseases: odor
o Ammoniacal = urea splitting bacterial infection
o Maple syrup = maple syrup urine disease
o Sweet/fruity = indicative of ketones
o Asparagus = mercaptopurines
o Musty or mousy = phenylketonuria
o Sweaty feet = isovaleric or glutaric academia
o Rancid = hypermethioninemia; tyrosinemia
Specific gravity in urinalysis
o Function of the number and weight of dissolved particles
o A convenient and rapid indicator of osmolality
o SPF 1.001 – 1.035 corresponds to 50-1000 mOsm/kg
Types of measurement:
• Urinometer/hydrometer more accurate (but requires large amount of urine)
• Refractometer only nees one drop
Dipstick SPG = least accurate
o Underestimated when pH >6.5
o Overestimated when urinary protein > 7.0 g/L
Uses:
SPG ~1.010 = Isosthenuric urine
• Solute diuresis accompanying hyperglycemia, diuretics or post-obstruction state
• Kidney has lost ability to concentrate urine (urine osmolality = plasma)
SPG < 1.004 = Hypostheuric urine
• Water diuresis from overhydration or diabetes insipidus
SPG > 1.018 = Hypersthenuric urine
• Implies preserved concentrating ability in presence of proteinuria/glycosuria
SPG > 1.040 = extrinsic osmotic agent (ex: contrast)
