In Office Procedures 3rd year 2nd semester Flashcards
Which urine sample collection method is preferred for routine urine culture and sensitivity testing?
A) Random sample
B) Midstream clean catch
C) First morning sample
D) Suprapubic bladder aspiration
Answer: B) Midstream clean catch
✅ Correct: Midstream clean catch is preferred for routine urine culture and sensitivity because it reduces contamination from external bacteria.
❌ Incorrect Answers:
A) Random sample: Often used for general urinalysis but is more prone to contamination.
C) First morning sample: Provides the most concentrated urine but is not specifically used for culture and sensitivity.
D) Suprapubic bladder aspiration: Invasive and only used in special cases where other methods are not feasible.
What is the most common complication of urine sample collection?
A) Hematuria
B) False positive and negative results
C) Urinary retention
D) Catheter-associated infections
Answer: B) False positive and negative results
✅ Correct: The main issue with urine collection is contamination or improper handling, leading to false positives or negatives in urinalysis.
❌ Incorrect Answers:
A) Hematuria: Not a direct complication of sample collection but can be a finding in urinalysis.
C) Urinary retention: Not a complication of routine collection, but can be relevant in catheterized patients.
D) Catheter-associated infections: Only a concern for catheterized urine collection, not routine sample collection.
Which of the following findings in a urinalysis is most concerning for a urinary tract infection (UTI)?
A) Presence of bilirubin
B) Presence of nitrites and leukocyte esterase
C) Presence of glucose and ketones
D) Low specific gravity
Answer: B) Presence of nitrites and leukocyte esterase
✅ Correct: The presence of nitrites (produced by certain bacteria) and leukocyte esterase (indicating white blood cells) strongly suggests a UTI.
❌ Incorrect Answers:
A) Bilirubin: Suggests liver disease, not a UTI.
C) Glucose and ketones: Indicative of diabetes or metabolic issues, not infection.
D) Low specific gravity: Suggests diluted urine, possibly due to excessive fluid intake or diabetes insipidus.
Why should urine samples be refrigerated if not analyzed immediately?
A) To prevent bacterial overgrowth
B) To preserve ketones and glucose
C) To maintain the pH balance
D) To make the urine easier to analyze under a microscope
Answer: A) To prevent bacterial overgrowth
✅ Correct: Refrigeration (2-8°C) prevents bacterial growth and chemical changes that can alter urinalysis results.
❌ Incorrect Answers:
B) Preserve ketones and glucose: Glucose can degrade over time, but refrigeration does not specifically preserve it.
C) Maintain pH balance: Refrigeration slows pH changes but does not completely prevent them.
D) Make it easier for microscopic analysis: Refrigeration prevents cell lysis, but warming the sample before analysis is still required.
Urine Sample + Urinalysis
Procedure: (continued)
4. A complete formal urinalysis includes 3 parts (clinically, practitioners primarily
assess gross appearance and dipstick analysis)
a. Gross appearance - check appearance (colour, turbidity and odour)
b. Dipstick analysis
- Insert the test strip into the sample of urine to ensure the reagent strips
has been fully immersed.
- Remove test strip and place horizontally on paper towel.
- Interpret each result at the appropriate time interval (typically starts at 30 seconds, then 60 seconds and should be completed by 120 seconds) by lining the urinalysis strip with the relevant row on the container.
What should be done if urinalysis dipstick analysis cannot be performed immediately?
A) Store the sample at room temperature
B) Refrigerate the sample at 2-8°C
C) Add a preservative to the sample
D) Discard the sample and request a new one
Answer: B) Refrigerate the sample at 2-8°C
✅ Correct: Refrigeration helps maintain the integrity of the urine sample by preventing bacterial overgrowth and cell degradation.
❌ Incorrect Answers:
A) Store at room temperature: Leads to bacterial growth and degradation of urine components.
C) Add a preservative: Not standard practice for routine urinalysis.
D) Discard and request a new one: Only necessary if the sample is too old or improperly stored.
Urine Sample + Urinalysis
Procedure:
1. Provide patient with sterile specimen container +/- cleansing wipe and access to washroom. Ensure specimen container has patient identifiers and date of sampling.
2. Practitioner puts on gloves to handle the patient’s specimen container. Ensure test strips have not expired and remove 1 strip. Be sure to close the air-tight container firmly and promptly to reduce exposure to air.
3. For routine urinalysis, a fresh (<2hr), clean catch sample is preferred. If analysis cannot be performed immediately, refrigerate the sample (2-8oC). This prevents casts and red blood cells from undergoing lysis and alkalization of the sample due to the precipitation of salts. Prior to assessment, be sure to rewarm refrigerated samples to room temperature.
A urine sample can typically be refrigerated for up to 24 hours before analysis. However, for the most accurate results, it should be examined within two hours of collection. Prolonged storage can lead to bacterial overgrowth, pH changes, and degradation of formed elements.
A patient’s urine sample is dark red-brown in color. Which of the following is the least likely cause?
A) Metronidazole use
B) Rhabdomyolysis
C) Biliary obstruction
D) Hematuria
Answer: C) Biliary obstruction
✅ Correct: Biliary obstruction typically leads to pale, clay-colored stools and dark urine due to bilirubin but does not cause dark red-brown urine.
❌ Incorrect Answers:
A) Metronidazole: Can cause dark red-brown urine as a side effect.
B) Rhabdomyolysis: Can lead to myoglobinuria, causing dark urine.
D) Hematuria: Blood in the urine can give it a red or brownish tint.
What is the recommended time frame for reading results on a urinalysis dipstick?
A) Immediately after removing the strip from the urine
B) At least 5 minutes after dipping
C) 30-120 seconds after dipping, depending on the reagent
D) Results can be read at any time within an hour
✅ Correct: Different reagents on the dipstick require specific timing (e.g., leukocytes take 120 seconds, others may take 30-60 seconds).
❌ Incorrect Answers:
A) Immediately after removing: Not enough time for reagents to react.
B) At least 5 minutes: Results would be inaccurate due to reagent breakdown.
D) Within an hour: Delayed readings may lead to false results due to exposure to air.
Urine Sample + Urinalysis
Procedure: (continued)
4. A complete formal urinalysis includes 3 parts (clinically, practitioners primarily
assess gross appearance and dipstick analysis)
a. Gross appearance - check appearance (colour, turbidity and odour)
b. Dipstick analysis
- Insert the test strip into the sample of urine to ensure the reagent strips
has been fully immersed.
- Remove test strip and place horizontally on paper towel.
- Interpret each result at the appropriate time interval (typically starts at 30 seconds, then 60 seconds and should be completed by 120 seconds) by lining the urinalysis strip with the relevant row on the container.
Which of the following steps is NOT part of urine sediment examination?
A) Centrifuging the urine sample
B) Decanting and discarding the supernatant
C) Immersing a urine dipstick into the sample
D) Examining under a microscope at different magnifications
Correct Answer: C
Explanation: Urine sediment examination involves centrifugation, discarding the supernatant, and microscopic examination. Dipstick analysis is a separate part of urinalysis and does not involve centrifugation.
What does “decant” and “supernatant” mean?
Decant: To carefully pour off the liquid portion of a sample without disturbing the sediment at the bottom.
Supernatant: The clear liquid that remains above the sediment after centrifugation. In urinalysis, the supernatant is discarded, and the sediment is examined under a microscope.
Which objective lens is initially used to examine urine sediment under a microscope?
A) 4X
B) 10X
C) 40X
D) 100X
Correct Answer: B
Explanation: The 10X objective lens is used first to examine urine sediment, particularly for casts, epithelial cells, and mucus. The 40X lens is later used for more detailed examination of red blood cells, white blood cells, bacteria, and parasites.
Why should the urine sample be well-mixed before sediment analysis?
A) To ensure uniform distribution of cells and casts
B) To increase the visibility of bacteria
C) To separate red blood cells from white blood cells
D) To remove excess proteins
Correct Answer: A
Explanation: Proper mixing ensures that all elements, such as cells and casts, are evenly distributed in the sample, leading to an accurate microscopic assessment.
What does it mean to ensure uniform distribution of cells and casts?
Ensuring uniform distribution means properly mixing the urine sediment before examining it under a microscope. This is done by flicking the centrifuge tube, which helps evenly disperse cells, casts, and other formed elements. Proper mixing prevents clumping and ensures an accurate microscopic analysis.
What is the significance of a positive leukocyte esterase test in urinalysis?
A) It confirms the presence of kidney stones
B) It suggests the presence of white blood cells, indicating possible infection
C) It indicates glucose in the urine, suggestive of diabetes
D) It confirms liver disease
Correct Answer: B
Explanation: Leukocyte esterase is an enzyme found in white blood cells, and its presence in urine typically suggests infection or inflammation, such as a urinary tract infection (UTI).
Leukocyte esterase is an enzyme released by white blood cells (WBCs). Its presence in urine suggests inflammation or infection, such as a urinary tract infection (UTI). A positive leukocyte esterase test typically indicates pyuria (pus in urine) and may be followed by a microscopic examination or urine culture to identify the causative bacteria.
A patient’s urine sample has a strong ammonia smell. What is the most likely cause?
A) Normal urine odor
B) Urinary tract infection (UTI) or dehydration
C) Phenylketonuria (PKU)
D) Maple syrup urine disease
Correct Answer: B
Explanation: A strong ammonia odor can result from bacterial activity in a UTI or concentrated urine due to dehydration. Phenylketonuria and maple syrup urine disease have distinct odors unrelated to ammonia.
A urine sample shows the presence of nitrites. What does this suggest?
A) The patient has kidney failure
B) The patient has a bacterial UTI
C) The patient has liver disease
D) The patient is dehydrated
Correct Answer: B
Explanation: Some bacteria that cause UTIs convert nitrates to nitrites, making a positive nitrite test a strong indicator of a bacterial infection.
Which of the following urine findings is most suggestive of diabetes mellitus?
A) High specific gravity
B) Positive glucose test
C) Presence of ketones
D) All of the above
Correct Answer: D
Explanation: Diabetes mellitus can cause glucose to appear in urine (glycosuria), an increase in specific gravity due to excess solutes, and the presence of ketones in uncontrolled diabetes.
low specific gravity is associated with diabetes insipidus, not diabetes mellitus.
Diabetes mellitus: Causes high specific gravity due to excess glucose in urine, which increases urine concentration. It may also lead to glycosuria (glucose in urine) and ketonuria (ketones in urine) in uncontrolled cases.
Diabetes insipidus: Causes low specific gravity because the kidneys fail to concentrate urine, leading to excessive water loss and dilute urine.
What is the normal range for urine pH?
A) 2.0 - 4.0
B) 4.6 - 8.0
C) 7.0 - 9.5
D) 5.5 - 10.0
A) 2.0 - 4.0 → Too acidic (not physiologically normal)
Could indicate contamination, improper sample handling, or an extremely acidic diet.
C) 7.0 - 9.5 → Alkaline urine (above normal range)
May be seen in UTIs, renal tubular acidosis, or after meals (postprandial alkaline tide).
D) 5.5 - 10.0 → Wider range than normal
While 5.5 is within the normal range, a pH of 10.0 is too high and could suggest bacterial contamination, prolonged sample storage, or alkalinization from medications like sodium bicarbonate.
A cloudy urine sample may indicate which of the following?
A) Phosphaturia
B) Pyuria (pus in urine)
C) Lipiduria
D) All of the above
Correct Answer: D
Explanation: Cloudy urine can result from phosphate crystals (phosphaturia), pus cells (pyuria), or fat globules (lipiduria), among other causes.
What condition is suggested by urine with a maple syrup-like odor?
A) Diabetes mellitus
B) Phenylketonuria (PKU)
C) Maple syrup urine disease
D) Cystinuria
Correct Answer: C
Explanation: Maple syrup urine disease is a metabolic disorder that causes urine to have a characteristic sweet odor due to an inability to break down branched-chain amino acids.
What is the primary indication for a skin scraping using mineral oil?
A) Suspected fungal infection
B) Suspected bacterial infection
C) Suspected scabies infestation
D) Suspected viral infection
Correct Answer: C) Suspected scabies infestation
Explanation: Skin scraping with mineral oil is specifically used to diagnose scabies by detecting mites, eggs, or scybala (feces) under the microscope.
A) Incorrect – Fungal infections are better detected using KOH preparation rather than mineral oil.
B) Incorrect – Bacterial infections are typically diagnosed via cultures or swabs, not skin scraping.
D) Incorrect – Viral infections (e.g., herpes) are diagnosed through Tzanck smear, PCR, or serology, not skin scraping.
**Skin Scraping - Mineral Oil (Scabies)
Procedure: **
Wear gloves during the collection of specimens.
Using a pencil, label the slide with the patient’s name and the date
Place a drop of mineral oil on the scalpel blade.
Allow some of the oil to flow onto the papule
Scrape vigorously across the lesions to remove the top of the papule. Scrapings must be taken from infected areas as mites are under the skin surface.
Transfer the oil and scraped material to glass slide
Place the second slide on top and seal together with tape or elastic bands
Place the slide in the sterile container
Discard the scalpel blade appropriately
Label container with patient name, date of birth and date of collection.
Place container in plastic biohazard bag and keep specimen at room temperature. Transport the laboratory as soon as possible.
What is the purpose of using potassium hydroxide (KOH) in a dermatophyte skin scraping?
A) To dissolve keratin and visualize fungal elements
B) To kill bacteria on the skin
C) To detect scabies mites
D) To remove the outer layer of the epidermis
Correct Answer: A) To dissolve keratin and visualize fungal elements
Explanation: KOH dissolves keratin in skin, hair, and nail samples, making it easier to see fungal hyphae and spores under the microscope.
B) Incorrect – KOH does not kill bacteria; alcohol swabs are used for that.
C) Incorrect – KOH is not used for scabies detection; mineral oil is preferred.
D) Incorrect – KOH does not physically remove skin layers; it is used for microscopic examination.
Skin Scraping Dermatophyte/KOH
Potassium hydroxide dissolves keratin in skin/hair/nail samples to visualize fungal elements (hyphae, spores)
Indications: suspected fungal or yeast infestation (e.g. tinea/ringworm)
Contraindications: none
Complications:
potential risk for bleeding at scraped site
Supplies: alcohol swab or sterile water, collection kit (black paper, envelope, etc)
Which of the following is an alternative method for detecting scabies?
A) KOH prep
B) Wood’s lamp examination
C) Tape-stripping test
D) Diascopy
Correct Answer: C) Tape-stripping test
Explanation: The tape-stripping test involves pressing transparent tape over a suspected burrow, removing it, and placing it on a slide to look for mites or eggs.
A) Incorrect – KOH prep is for fungal infections, not scabies.
B) Incorrect – Wood’s lamp is used to detect fluorescent infections, not mites.
D) Incorrect – Diascopy is used to assess whether a lesion blanches, not for scabies detection.
Skin Scraping Scabies
Indications: suspected scabies infestation
Contraindications: none
Complications:
potential risk for bleeding at scraped site
Supplies: sterile scalpel blade, mineral oil, glass slide, tape, sterile transport container, elastic bands
Alternative: tape-stripping test - press transparent tape over the burrow, pull it off, and place it onto a slide.
What does the “spaghetti and meatballs” appearance under KOH prep suggest?
A) Tinea corporis
B) Tinea versicolor
C) Scabies infestation
D) Pediculosis (lice)
Correct Answer: B) Tinea versicolor
Explanation: Tinea versicolor (caused by Malassezia) presents as yeasts and pseudohyphae under KOH prep, resembling “spaghetti and meatballs.”
A) Incorrect – Tinea corporis (ringworm) shows branching hyphae with cross-striations.
C) Incorrect – Scabies is diagnosed with mineral oil skin scraping, not KOH.
D) Incorrect – Pediculosis (lice) is usually visible without microscopy and may fluoresce under a Wood’s lamp.
Which of the following conditions can be diagnosed using a Wood’s lamp?
A) Corynebacterium infection
B) Scabies
C) Psoriasis
D) Lichen planus
Correct Answer: A) Corynebacterium infection
Explanation: Corynebacterium (which causes erythrasma) fluoresces coral-red under a Wood’s lamp.
B) Incorrect – Scabies does not fluoresce and is diagnosed with mineral oil scraping.
C) Incorrect – Psoriasis is diagnosed clinically or with biopsy, not Wood’s lamp.
D) Incorrect – Lichen planus does not fluoresce and is identified by its characteristic morphology.
Which of the following scrapings should NOT be stored in the refrigerator?
A) KOH skin scraping for dermatophyte infection
B) Mineral oil scraping for scabies
C) Bacterial culture swab
D) Nail clipping for fungal culture
Correct Answer: A) KOH skin scraping for dermatophyte infection
Explanation: KOH samples should be stored at room temperature to prevent artifact formation and degradation of fungal structures.
B) Incorrect – Scabies samples should also be kept at room temperature for accurate microscopic detection.
C) Incorrect – Bacterial cultures should be refrigerated to slow bacterial overgrowth before lab testing.
D) Incorrect – Nail clippings for fungal culture should be refrigerated to prevent contamination.
Skin Scraping KOH (Dermatophyte, tinea, Mites)
Procedure:
Clean the infected site with 70% alcohol (or sterile water if inflamed) to eliminate body bacteria. Allow to air dry.
Collect specimens onto the black paper provided in the Dermatophyte Collection Kit. The active periphery of the infected site should be scraped with a scalpel blade onto the black paper. Carefully fold the paper so the skin scrapings are enveloped inside.
Label the envelope with the patient name, date of birth, date of collection and specimen type and anatomical site. Do not label as just a skin as the exact site is required (i.e. ‘skin from elbow’, ‘skin from chest’, ‘right big toenail’)
Place the envelope inside the plastic bag provided with the kit and seal.
Store and transport at room temperature – do not refrigerate
Which of the following conditions is associated with the presence of hyphae with cross-striations under KOH prep?
A) Tinea corporis
B) Tinea versicolor
C) Candidiasis
D) Psoriasis
Correct Answer: A) Tinea corporis
Explanation: Tinea corporis (ringworm) is caused by dermatophytes, which appear as branching hyphae with cross-striations under KOH prep.
B) Incorrect – Tinea versicolor shows yeasts + pseudohyphae (“spaghetti and meatballs”), not hyphae with cross-striations.
C) Incorrect – Candidiasis shows only pseudohyphae, not true hyphae with cross-striations.
D) Incorrect – Psoriasis is a non-infectious condition and does not show hyphae.
Skin Scraping interpretation
Hyphae with cross-striations - suggests dermatophytes (tinea infection, named based on anatomical location - tinea corporis (body), tinea cruris (jock itch), tinea pedis (athlete’s foot), tinea capitis (scalp), tinea unguium (onychomycosis))
“Spaghetti and meatballs” (yeasts + pseudohyphae) - suggests tinea versicolor (Malassezia, not a true dermatophyte)
Mites, eggs, or scybala - suggests scabies infestation
Pseudohyphae - suggest candidal infection
If negative results on initial KOH but high clinical suspicion, send sample for culture or periodic acid–Schiff (PAS) stain
What is a potential complication of skin scraping?
A) Infection
B) Severe pain
C) Bleeding at the scraped site
D) Tissue necrosis
Correct Answer: C) Bleeding at the scraped site
Explanation: Skin scraping may cause minor bleeding, but serious complications are rare.
A) Incorrect – Infection is unlikely since sterile techniques are used.
B) Incorrect – Skin scraping is typically mildly uncomfortable rather than severely painful.
D) Incorrect – Tissue necrosis does not occur from simple skin scraping.
Which of the following substances can cause a false-negative glucose result on a urine dipstick test?
A) Vitamin C
B) Bilirubin
C) Ketones
D) Bacteria
✅ Correct Answer: A) Vitamin C
Explanation:
Vitamin C (ascorbic acid) is a strong reducing agent that interferes with the glucose oxidase reaction, leading to false-negative glucose results.
❌ B) Bilirubin – Does not interfere with the glucose test but may cause false-negative bilirubin results.
❌ C) Ketones – Do not affect glucose detection but can cause false positives in some other tests.
❌ D) Bacteria – Can increase glucose metabolism in urine, but they do not cause false negatives directly.
1) Urinalysis – False Negative for Blood and Glucose
Blood (Hematuria & Hemoglobinuria)
Many urine dipsticks use a peroxidase reaction to detect blood.
Vitamin C inhibits peroxidase activity, leading to false negatives even if blood is present.
Glucose (Glycosuria)
Glucose is detected using glucose oxidase, which converts glucose into hydrogen peroxide and produces a color change.
Vitamin C reduces hydrogen peroxide, preventing the color reaction and leading to a false-negative glucose test.
2) False-Negative Leukocyte Esterase Test
Leukocyte esterase detects white blood cells (WBCs) in urine, which can indicate infection.
Vitamin C interferes with the enzymatic reaction that produces the color change, leading to false-negative results.
3) False-Negative Bilirubin Test
The bilirubin dipstick uses a diazo reaction to produce color.
Vitamin C prevents the formation of the colored product, leading to falsely low or undetectable bilirubin levels.
4) Impact on Fecal Occult Blood Test (FOBT)
The guaiac test for occult blood in stool relies on a peroxidase reaction (similar to urine blood tests).
Vitamin C reduces the peroxidase activity, leading to false negatives.
Summary
Vitamin C interferes with tests by reducing key reaction products in chemical-based dipstick assays. This is why many lab instructions advise avoiding high doses of vitamin C before urine and stool tests.
Which of the following can cause a false-positive blood (hematuria) test on a urine dipstick?
A) Myoglobin
B) Ascorbic acid
C) High protein diet
D) Leukocytes
✅ Correct Answer: A) Myoglobin
Explanation:
Myoglobin (from muscle breakdown, e.g., rhabdomyolysis) reacts with the same peroxidase-based test as hemoglobin, leading to a false-positive blood result.
❌ B) Ascorbic acid (Vitamin C) – Actually causes a false negative, not a false positive, by inhibiting peroxidase activity.
❌ C) High protein diet – Can acidify urine but does not directly cause false-positive blood tests.
❌ D) Leukocytes – Do not affect the blood test but can produce a separate positive leukocyte esterase result.
Which condition is most likely to cause a false-positive leukocyte esterase test?
A) High vitamin C intake
B) Vaginal contamination
C) Urobilinogen presence
D) High urine glucose
✅ Correct Answer: B) Vaginal contamination
Explanation:
Vaginal discharge (including WBCs from infection or contamination) can lead to a false-positive leukocyte esterase test, even if no UTI is present.
❌ A) High vitamin C intake – Actually causes false negatives by interfering with the leukocyte esterase reaction.
❌ C) Urobilinogen presence – Does not interfere with the leukocyte esterase test.
❌ D) High urine glucose – Can affect other tests (e.g., specific gravity, glucose), but not leukocyte esterase directly.
A urine sample tests positive for nitrites, but the patient has no infection symptoms. What could explain this false-positive result?
A) High vitamin C intake
B) Improper storage of the urine sample
C) Presence of ketones
D) Low urine pH
✅ Correct Answer: B) Improper storage of the urine sample
Explanation:
Prolonged storage at room temperature can lead to bacterial growth, converting nitrates into nitrites and causing a false-positive nitrite result.
❌ A) High vitamin C intake – Actually causes false negatives by preventing nitrite formation.
❌ C) Presence of ketones – Does not cause false positives for nitrites.
❌ D) Low urine pH – Can affect other tests but does not directly cause false-positive nitrites.
A urine dipstick shows a false-positive protein (albuminuria) test. Which of the following is the most likely cause?
A) Highly alkaline urine
B) High vitamin C intake
C) Presence of glucose
D) Low urine specific gravity
✅ Correct Answer: A) Highly alkaline urine
Explanation:
Strongly alkaline urine (pH >8.0) can cause a false-positive protein reading on dipstick tests due to interference with the color change reaction.
❌ B) High vitamin C intake – More commonly causes false negatives rather than false positives.
❌ C) Presence of glucose – Does not interfere with protein measurement.
❌ D) Low urine specific gravity – Can dilute urine but does not cause false-positive protein results.
Which of the following skin conditions will NOT blanch under diascopy?
A) Purpura
B) Inflammatory erythema
C) Cutaneous sarcoidosis
D) Psoriasis
Answer: A) Purpura
Explanation: Purpura does not blanch because it results from extravasation of blood into the skin. Inflammatory erythema
(B) blanches because it is due to vasodilation, while cutaneous
(C) sarcoidosis may show an “apple jelly” color under diascopy.
(D) Psoriasis is not diagnosed with diascopy.
Diascopy - involves pressing a transparent slide firmly on a lesion to see if it blanches
Purpura does not blanch
Inflammatory erythema will blanch
Granulomatous lesion (e.g. cutaneous sarcoidosis) - an “apple jelly” colour can appear
What color does Microsporum canis fluoresce under a Wood’s Lamp?
A) Green
B) Coral-red
C) Blue
D) Yellow
Answer: A) Green
Explanation: Microsporum canis fluoresces green under a Wood’s Lamp. Corynebacterium fluoresces coral-red (B), (C) and (D) while blue and yellow are not characteristic colors of these infections.
Wood’s Lamp Examination - can detect if certain infections fluoresce (characteristic colours) and subtle pigment changes (to help differentiate hypopigmentation vs. depigmentation)
Microsporum canis - green
Corynebacterium - coral-red
Pseudomonas - green
Under potassium hydroxide (KOH) preparation, which of the following would show the “spaghetti and meatballs” appearance?
A) Tinea versicolor
B) Tinea corporis
C) Scabies
D) Lichen planus
Answer: A) Tinea versicolor
Explanation: Tinea versicolor
(A) shows the characteristic “spaghetti and meatballs” appearance due to yeast and pseudohyphae.
(B) Tinea corporis shows branching hyphae, (C) scabies is identified by mites and eggs,(D) lichen planus does not have fungal elements.
Which of the following is a key feature of tinea (ringworm) infections under KOH microscopy?
A) “Spaghetti and meatballs” appearance
B) Branching hyphae with cross-striations
C) Apple jelly color
D) Coral-red fluorescence
Answer: B) Branching hyphae with cross-striations
Explanation:
(B) Tinea infections show branching hyphae with cross-striations under KOH. The “spaghetti and meatballs” appearance (A) is seen in tinea versicolor. “Apple jelly” (C) refers to cutaneous sarcoidosis under diascopy. Coral-red fluorescence (D) is characteristic of Corynebacterium under a Wood’s Lamp.
How can pediculosis (lice) be detected?
A) It can only be seen under a microscope
B) It fluoresces green under a Wood’s Lamp
C) It may be visible on skin or hair without additional tools
D) It shows a “spaghetti and meatballs” pattern under KOH
Answer: C) It may be visible on skin or hair without additional tools
Explanation: Pediculosis (C) is often visible without magnification. It may also fluoresce under a Wood’s Lamp, but the fluorescence is not green
(B). Lice do not require KOH examination
(D) and are not exclusively microscopic (A).
tinea versicolor (Malassezia)
scrapings often show abundant “spaghetti and meatballs” appearance (yeasts + pseudohyphae) under KOH prep
lateral stretching of the skin can make fine, branny scale more apparent (aka. tinea versicolor scale sign)
tinea (dermatophyte/ringworm) infections
scrapings show branching hyphae with cross-striations under KOH (yields may be lower, so scrape edges thoroughly)
scabies
scraping reveals mites, eggs, or scybala (mite feces) under microscope
pediculosis (lice) - may be visible on skin or hair without additional tools
may fluoresce under Wood’s lamp or can remove hair or nits for closer microscopic examination (if necessary)
