★ Must-know
The chain of infection has six components:
Handwashing breaks the chain of infection; wash visibly soiled hands with soap and water, and use alcohol-based hand rub when hands are not visibly soiled.
Add acid to water because adding water to acid can cause an explosion.
🔄 The RACE fire response is:
Further detail
📌 Biological waste other than urine belongs in biohazard-labeled containers, while urine is poured carefully into a laboratory sink and flushed with water.
RACE moves from Rescue and Alarm to Contain and Extinguish or Evacuate.
★ Must-know
📌 The glomerulus filters plasma substances smaller than 70,000 daltons, while the negatively charged filtration barrier restricts albumin despite its size permitting passage.
Further detail
Each kidney contains approximately 1 to 1.5 million nephrons.
🔄 Renal blood flow follows this route:
The kidneys receive 25% of total cardiac output, with total renal blood flow of 1200 mL/min and renal plasma flow of 600 to 700 mL/min.
The descending loop reabsorbs water; the ascending loop reabsorbs salt but is impermeable to water.
★ Must-know
📌 Clearance tests evaluate glomerular filtration, whereas concentration tests evaluate tubular reabsorption and the kidney’s ability to concentrate or dilute urine.
📐 Formula - Creatinine clearance is calculated as , where U is urine creatinine, V is urine flow in mL/min, P is plasma creatinine, and A is body surface area.
Further detail
📌 The greatest source of error in urine-based clearance testing is an improperly timed urine specimen, and creatinine clearance also reflects the completeness of a 24-hour urine collection.
Clearance tests assess glomerular filtration; concentration tests assess tubular reabsorption.
★ Must-know
📌 A first-morning urine specimen is concentrated and acidic and is preferred for routine urinalysis and pregnancy testing, whereas a second-morning fasting specimen is used for glucose determination.
In the three-glass technique, the patient provides initial, midstream, and post-prostatic-massage urine; prostatitis is indicated when the third specimen has ten times more white blood cells and bacteria than the first, while a positive second specimen invalidates the comparison.
Drug testing requires 30–45 mL of urine in a 60 mL container, with specimen temperature checked within four minutes and expected to be 32.5–37.7°C.
📌 Urine should be tested within two hours of collection, and when routine urinalysis and culture are both requested, culture should be performed first.
Further detail
📌 A 24-hour urine collection begins by discarding the first void and ends by including the final void at the designated end time.
★ Must-know
Normal urine is 95–97% water and 3–5% solids, with chloride the major inorganic component and urea the major organic component.
Normal 24-hour urine volume is 600–2,000 mL, with an average of 1,200–1,500 mL.
Random urine specific gravity is 1.003–1.035, first-morning specific gravity is greater than 1.020, and a value above 1.040 suggests radiographic dye.
Further detail
📌 Polyuria is urine output greater than 2,000 mL per 24 hours in adults, whereas oliguria is below 500 mL per 24 hours according to Henry.
📌 Urine clarity ranges from clear, with no visible particles, through hazy and cloudy to turbidity, where print cannot be seen through the specimen.
★ Must-know
📌 Pre-renal overflow proteinuria results from excess plasma proteins before blood reaches the kidney, renal proteinuria arises from glomerular or tubular disease, and post-renal proteinuria arises from sources downstream of the kidney.
Causes of overflow proteinuria include: intravascular hemolysis producing hemoglobin, muscle injury producing myoglobin, severe infection or inflammation increasing acute-phase reactants, multiple myeloma producing Bence-Jones protein
Normal albumin excretion rate is 0–20 μg/min, microalbuminuria is 20–200 μg/min or 30–300 mg/24 hours, and clinical albuminuria is greater than 200 μg/min.
Further detail
Bence-Jones proteins are immunoglobulin light chains of matching type, either κ–κ or λ–λ, produced by proliferating immunoglobulin-producing plasma cells in multiple myeloma.
🔄 The characteristic heat-test sequence is: urine becomes cloudy at 40–60°C, urine clears at 100°C, after hot filtration, turbidity reappears as the specimen cools through 40–60°C
Pre-renal is before the kidney; renal is within it; post-renal is after it.
★ Must-know
📌 Hyperglycemia-associated glucosuria occurs with increased blood glucose, whereas renal glucosuria occurs with normal blood glucose because tubular glucose reabsorption is impaired, as in Fanconi syndrome.
The urine reagent strip for glucose detects glucose through sequential glucose oxidase and peroxidase reactions, has a sensitivity of 100 mg/dL, and may give false-negative results with high ascorbic acid, ketones, high specific gravity, low temperature, or improperly preserved specimens.
Clinitest is a nonspecific copper-reduction test for reducing sugars including glucose, galactose, lactose, and fructose, but not non-reducing sucrose.
Ketones result from increased fat metabolism when carbohydrates cannot be metabolized, and the stated renal threshold is 70 mg/dL.
Urinary ketone bodies are approximately 78% beta-hydroxybutyric acid, 20% acetoacetic acid, and 2% acetone; reagent strips detect acetoacetic acid, while acetone is detected only when glycine is present.
Further detail
★ Must-know
🔄 Routine sediment preparation proceeds by: transferring 10–15 mL urine to a tube, centrifuging at 400 RCF for 5 minutes, decanting while leaving 0.5–1.0 mL, transferring 20 μL sediment to a slide for microscopic examination
Bright-field microscopy is used for routine urinalysis, phase-contrast microscopy enhances translucent elements such as casts, and polarizing microscopy detects birefringence and helps identify cholesterol in oval fat bodies and fatty casts.
Further detail
📌 If less than 12 mL urine is available, centrifuge 3 mL; if less than 3 mL is available, examine the sediment without centrifugation.
Sternheimer–Malbin stain is the most commonly used urine sediment stain and helps identify white blood cells, epithelial cells, and casts by contrasting nuclear and cytoplasmic structures.
The Addis count quantitatively measures urinary formed elements using a 12-hour urine specimen preserved with formalin; normal values are 0–500,000 RBCs, 0–1,800,000 WBCs and epithelial cells, and 0–5,000 hyaline casts per 12 hours.
★ Must-know
Urinary RBC reference values are 0–2 or 0–3 per high-power field, and RBCs swell and may lyse in hypotonic urine but crenate in hypertonic urine.
More than 2 renal tubular epithelial cells per high-power field indicates tubular injury, and lipid-containing renal tubular cells can form oval fat bodies associated with lipiduria such as in nephrotic syndrome.
📌 A true urinary tract infection is supported by bacteria together with white blood cells, whereas bacteria alone may indicate contamination or an old specimen; yeast alone likewise may indicate contamination.
📌 RBC casts indicate bleeding within the nephron, whereas WBC casts indicate inflammation or infection within the nephron; a clump of leukocytes from a lower UTI is a pseudoleukocyte cast and must not be reported as a true cast.
Further detail
★ Must-know
Urinary crystals form by precipitation of urine solutes, and their formation is influenced by pH, solute concentration, and temperature; crystals in fresh urine are most often associated with a concentrated specimen.
Calcium oxalate is the most frequently observed urinary crystal; its dihydrate form is commonly envelope-shaped, while its monohydrate form may be oval or dumbbell-shaped.
📌 Uric acid crystals are yellow-brown and birefringent, while cystine crystals are colorless hexagonal plates and are not birefringent; both are soluble in ammonia, but cystine is soluble in dilute hydrochloric acid and uric acid is not.
Further detail
Amorphous phosphates are a common cause of turbidity in alkaline urine and dissolve in dilute acetic acid; ammonium biurate and triple phosphate may occur with urea-splitting bacteria.
Cholesterol crystals are rectangular plates with notched corners and may occur in lipiduria, whereas radiographic dye crystals can resemble them and may be distinguished by patient history and urine findings.
Starch granules are spherical with a dimpled center and can show a Maltese-cross pattern under polarized microscopy, a feature they share with lipid-containing urinary elements.
★ Must-know
📌 Overflow aminoaciduria produces increased amino acids in both blood and urine, whereas renal aminoaciduria produces increased urine amino acids despite normal blood levels because tubular reabsorption is defective.
Phenylketonuria results from a missing gene coding for phenylalanine hydroxylase, causing increased urinary phenylpyruvic acid and a characteristic mousy odor of urine, sweat, and breath.
Maple syrup urine disease results from deficiency of branched-chain α-keto acid dehydrogenase, increases leucine, isoleucine, and valine ketoacids, and can give urine a maple-syrup or curry odor.
Cystinuria is a renal aminoaciduria caused by defective tubular reabsorption of cystine, ornithine, lysine, and arginine; cystine is the only one of these amino acids that crystallizes.
Further detail
A positive Guthrie bacterial inhibition test shows bacterial growth because phenylalanine counteracts the inhibitory action of B2-thienylalanine on B. subtilis.
Urinary homogentisic acid in alkaptonuria darkens when alkaline urine stands at room temperature, and the acid can cause black pigmentation of connective tissues and ears.
Overflow aminoaciduria raises blood and urine amino acids; renal aminoaciduria raises urine amino acids despite normal blood levels.
★ Must-know
📌 Membranous glomerulonephritis features glomerular membrane thickening after IgG immune-complex deposition, whereas minimal change disease has little cellular change and glomeruli that look normal by light microscopy.
📌 Cystitis typically shows white blood cells and bacteria without casts, whereas acute pyelonephritis can show white-cell and bacterial casts.
Further detail
Renal failure is associated with a glomerular filtration rate below 25 mL/min, azotemia, impaired concentrating ability causing isosthenuria, and a telescoped sediment containing varied casts.
Calcium oxalate is the major constituent of renal calculi; cystine calculi are the least common, and triple phosphate calculi can form branching staghorn stones with infections involving urea-splitting bacteria such as Proteus vulgaris.
Cystitis has bacteria without casts; pyelonephritis can produce white-cell casts.
★ Must-know
Human chorionic gonadotropin is produced by placental syncytiotrophoblast cells, peaks in the first trimester, and has an alpha subunit shared with LH, FSH, and TSH and a beta subunit that confers hCG specificity.
Normal amniotic fluid volume in the third trimester is 800–1,200 mL, and fetal urine is its major volume contributor after the first trimester.
An amniotic-fluid lecithin-to-sphingomyelin ratio greater than 2.0 indicates mature fetal lungs, but blood or meconium contamination can falsely increase the ratio.
Further detail
📌 The source labels increased amniotic fluid volume below 800 mL as polyhydramnios and decreased volume above 1,200 mL as oligohydramnios.
hCG alpha is shared with LH, FSH, and TSH; hCG beta confers specificity.
★ Must-know
An acceptable sputum specimen contains fewer than 10 squamous epithelial cells per low-power field and more than 25 white blood cells per low-power field.
Curschmann spirals, Creola bodies, and Charcot-Leyden crystals are associated with bronchial asthma.
The sweat test diagnoses cystic fibrosis, in which sweat sodium and chloride are increased because sweat glands cannot reabsorb them before secretion; values above 70 mEq/L are diagnostic.
Further detail
The preferred routine sputum specimen is the first-morning sample because it is most concentrated.
Sputum is approximately 95% water and 5% solids, and sialic acid is its most important single component for viscosity.
★ Must-know
📌 A traumatic tap typically shows decreasing blood across the three collection tubes, clot formation, and clear supernatant, whereas intracranial hemorrhage shows evenly distributed blood, no clot, and xanthochromic supernatant.
Normal adult cerebrospinal-fluid protein is 15–45 mg/dL, and damage to the blood-brain barrier is the most common cause of increased cerebrospinal-fluid protein.
A CSF/serum albumin index below 9 is normal; values of 9–14 indicate slight impairment, 15–30 moderate impairment, and above 30 severe impairment, while 100 indicates complete blood-brain barrier damage.
📐 Formula - The IgG index is calculated as and assesses intrathecal IgG production.
At least two oligoclonal bands in CSF that are absent from serum are valuable for diagnosing multiple sclerosis; electrophoresis of both fluids distinguishes CNS-restricted bands from bands also present in serum.
CSF glucose is normally 60–70% of blood glucose, or 50–80 mg/dL, and is decreased in bacterial, tubercular, and fungal meningitis but generally normal in viral meningitis.
Further detail
📐 Formula - The cerebrospinal-fluid albumin index is ; a value above 9 is abnormal and assesses blood-brain barrier integrity.
Two or more oligoclonal bands in cerebrospinal fluid that are absent from serum support the diagnosis of multiple sclerosis.
An IgG index above 0.77 is abnormal and indicates IgG production within the CNS; the cited Brunzel normal range is 0.30–0.70.
A traumatic tap clears across tubes; intracranial hemorrhage distributes blood evenly.
★ Must-know
🔄 Sperm maturation proceeds through:
The entire ejaculate should be collected and delivered at room temperature within 1 hour; analysis follows liquefaction, normally within 30–60 minutes, and samples awaiting analysis should be kept at 37°C.
Normal semen values include volume 2–5 mL, pH 7.2–8.0, sperm concentration above 20 million/mL, sperm count above 40 million per ejaculate, and motility above 50% within 1 hour.
Further detail
Semen consists of approximately 5% spermatozoa, 60–70% seminal-vesicle fluid, 20–30% prostatic fluid, and 5% bulbourethral-gland secretions.
Semen collection requires 2–3 days of abstinence, but not more than 7 days; prolonged abstinence increases volume and decreases motility.
📌 Routine sperm morphology criteria require more than 30% normal forms, whereas Kruger's strict criteria require more than 14%.
Spermatogonium → primary spermatocyte → secondary spermatocyte → spermatid → spermatozoon.
★ Must-know
📌 Monosodium urate crystals are needle-shaped and negatively birefringent in gout, whereas calcium pyrophosphate crystals are rhombic, square, or rod-shaped and positively birefringent in pseudogout.
Further detail
Normal synovial fluid is clear to pale yellow, does not clot, and forms a string 4–6 cm long; a normal adult knee cavity contains less than 3.5 mL.
Normal synovial-fluid WBC count is below 200/µL, while the normal differential contains 65% monocytes and macrophages, less than 25% neutrophils, and less than 15% lymphocytes.
The synovial-fluid glucose difference from blood is normally less than 10 mg/dL; glucose is decreased in inflammatory and infectious joint disorders.
MSU needles are negatively birefringent; CPPD crystals are positively birefringent.
📌 Transudates result from altered hydrostatic or oncotic pressure and fluid regulation, whereas exudates result from direct damage to a cavity membrane, such as from infection, inflammation, or malignancy.
📌 A fluid-to-serum protein ratio below 0.5 and LD ratio below 0.6 indicate transudate, whereas ratios above 0.5 and 0.6, respectively, indicate exudate.
📌 Altered motility may be enhanced (hypermotility) or slow, as in constipation.
With Sternheimer-Malbin stain, squamous cells appear pale purple with dark purple nuclei, renal cells have orange-purple cytoplasm and dark nuclei, and leukocytes appear pale pink with purple nuclei. - Handbook
With Sternheimer-Malbin stain, crystals do not stain; hyaline and waxy casts may be unstained or pale pink; granular casts have a pink matrix and purple granules; and red blood cell casts are red-purple. - Handbook
Pancreatic exocrine secretion contributes approximately 1,500 mL/day to duodenal contents and is a major contributor. - Henry, 17h Ed
Secretin and pancreozymin stimulate pancreatic secretion. - Henry, 17h Ed
Approximately 500–1,000 mL of bile enters the duodenum daily; bile is usually alkaline, yellow to brown or green, and has a pH of 7.0 to 8.5. - Henry, 17h Ed
Desquamative inflammatory vaginitis and atrophic vaginitis both have excessive purulent discharge, vaginal erythema, pH above 4.5, and 3+ to 4+ WBCs; lactobacilli are absent or reduced in desquamative inflammatory vaginitis and decreased in atrophic vaginitis. - Strasinger, 6th Ed
Bacterial vaginosis typically has thin white-to-gray discharge, pH above 4.5, rare or absent WBCs and lactobacilli, more than 20% clue cells, and a positive whiff test. - Strasinger, 6th Ed
Candidiasis typically has white, curd-like discharge, pH 3.8–4.5, 3+ to 4+ WBCs, lactobacilli present, large clumps of epithelial cells, budding yeast and pseudohyphae, and a negative whiff test. - Strasinger, 6th Ed
Trichomoniasis typically has increased-volume yellow-green frothy adherent discharge, pH above 4.5, increased WBCs, rare or absent lactobacilli, and a negative whiff test. - Strasinger, 6th Ed
The UF-1000i categorizes particles using:
Pre-analytical quality variables include assay selection for patient need and its implementation, patient identification and preparation, specimen collection, transport, preparation and storage, and monitoring specimen condition. - Rodak, 4th Ed
Transudates reflect pressure or regulation changes; exudates reflect membrane damage.
| Finding | Transudate | Exudate |
|---|---|---|
| Cause | Altered hydrostatic or oncotic pressure | Direct membrane damage |
| Fluid-to-serum protein ratio | Below 0.5 | Above 0.5 |
| Fluid-to-serum LD ratio | Below 0.6 | Above 0.6 |
| WBC count | Below 1,000/µL | Above 1,000/µL |
| Spontaneous clotting | Absent | Possible |
| Finding | Bacterial vaginosis | Candidiasis | Trichomoniasis |
|---|---|---|---|
| Appearance | Thin white to gray discharge | White, curd-like discharge | Yellow-green frothy adherent discharge |
| pH | Above 4.5 | 3.8–4.5 | Above 4.5 |
| Whiff test | Positive | Negative | Negative |
| Other findings | More than 20% clue cells | Budding yeast and pseudohyphae | Increased WBCs |
Take a 10-question practice quiz on Urinalysis and Body Fluid Analysis, with every answer explained.
1. The RACE fire-response sequence includes:
2. What is the nephron’s role and basic composition?
Memorize the key concepts of Urinalysis and Body Fluid Analysis with 10 flashcards.
What are the six components of the chain of infection?
Infectious agent, reservoir, portal of exit, mode of transmission, portal of entry, and susceptible host.
How should laboratory personnel wash their hands when visibly soiled versus not visibly soiled?
Use soap and water when visibly soiled, and alcohol-based hand rub when not visibly soiled.
What is the nephron’s role in the kidney?
It is the kidney’s basic structural and functional unit.
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