Master the essentials of preanalytic procedures in microbiology with this comprehensive mock test featuring 66 multiple-choice questions (MCQs) and detailed answers. Designed for laboratory professionals and students preparing for certification exams such as ASCP MLS, AMT MLT/MT, AIMS, CSMLS, IBMS, HAAD, DHA, and MOH, this practice test focuses on specimen collection, handling, and transport—critical steps for ensuring accurate microbiological results.
66 MCQs (1292 – 1357):
- Which of the following is the most critical factor affecting the accuracy of microbiological test results during the preanalytic phase?
a) Correct antibiotic therapy
b) Proper specimen collection and handling
c) Selection of culture media
d) Incubation temperature - What is the recommended time frame for transporting a cerebrospinal fluid (CSF) specimen for microbiological culture?
a) Within 24 hours at room temperature
b) Immediately, kept at room temperature
c) Within 2 hours, refrigerated
d) Within 6 hours on ice - Which of the following swab transport systems is most suitable for fastidious organisms such as Neisseria gonorrhoeae?
a) Dry cotton swab
b) Amies transport medium with charcoal
c) Normal saline
d) Sterile water - Why is blood culture collection performed before administering antibiotics?
a) To avoid contamination by skin flora
b) To prevent dilution of blood sample
c) To avoid suppression of bacterial growth
d) To reduce hemolysis of the sample - For optimal detection of anaerobic bacteria, what type of specimen collection is preferred?
a) Swab specimen in open air
b) Aspirate collected into a sterile syringe
c) Urine collected in a clean catch container
d) Saliva collected in a sterile cup - Which of the following actions can lead to rejection of a sputum specimen for culture?
a) Specimen delivered within 1 hour of collection
b) Specimen containing ≥25 WBCs per low-power field
c) Specimen containing >10 squamous epithelial cells per low-power field
d) Collection performed early in the morning - Which preservative is recommended for urine specimens collected for culture when immediate processing is not possible?
a) Boric acid
b) Formalin
c) EDTA
d) Sodium fluoride - The most common cause of contamination in blood cultures is:
a) Use of non-sterile needles
b) Improper site disinfection before collection
c) Inadequate volume of blood collected
d) Delayed transportation to the lab - Which of the following specimens should never be refrigerated before culture?
a) Stool for Salmonella detection
b) Throat swab for Group A Streptococcus
c) Cerebrospinal fluid for bacterial culture
d) Urine specimen for routine culture - Which is the preferred antiseptic for cleansing the venipuncture site before collecting blood cultures?
a) 70% isopropyl alcohol only
b) Povidone-iodine followed by alcohol
c) Soap and water
d) Hydrogen peroxide - The optimal volume of blood per culture bottle for adults is generally:
a) 1–2 mL
b) 5–10 mL
c) 20–30 mL
d) 50 mL - Which of the following factors most contributes to false-negative blood culture results?
a) Collection after initiation of antibiotics
b) Overfilling blood culture bottles
c) Use of proper skin disinfection
d) Multiple sets collected from different sites - Which type of container is most appropriate for collecting a tissue biopsy for anaerobic culture?
a) Dry sterile swab
b) Sterile, oxygen-free transport vial
c) Formalin-filled container
d) Non-sterile plastic bag - For optimal recovery of Bordetella pertussis, nasopharyngeal swabs should be made of:
a) Cotton
b) Rayon or Dacron
c) Calcium alginate
d) Wooden stick swabs - Delayed transport of stool specimens for ova and parasite (O&P) examination may lead to:
a) Increased parasite motility
b) Death and distortion of trophozoites
c) Increased bacterial overgrowth
d) Both “Death and distortion of trophozoites” and “Increased bacterial overgrowth” - Which of the following would cause rejection of a urine specimen for culture?
a) Specimen collected via catheterization
b) Specimen transported after 24 hours at room temperature
c) Specimen collected as a clean-catch midstream
d) Specimen preserved with boric acid - Which of the following is considered the least acceptable specimen for anaerobic culture?
a) Aspirated pus from a sterile site
b) Tissue biopsy placed in an oxygen-free vial
c) Swab from a superficial wound exposed to air
d) Synovial fluid collected by needle aspiration - Which preanalytic error most frequently leads to false-positive blood culture results?
a) Low blood volume inoculated
b) Use of povidone-iodine antiseptic
c) Contamination with skin flora during collection
d) Delay in incubating bottles - Why are throat swabs for Group A Streptococcus usually collected from the tonsillar area?
a) It contains the highest concentration of antibodies
b) It is the most common colonization site
c) The area is free of normal flora
d) It avoids saliva contamination - Which type of transport medium is most suitable for stool samples suspected of containing Vibrio cholerae?
a) Cary-Blair medium
b) Stuart’s medium
c) Amies medium
d) Buffered glycerol saline - What is the maximum acceptable delay for processing respiratory specimens for culture at room temperature?
a) 1 hour
b) 2 hours
c) 6 hours
d) 24 hours - Which of the following is the best specimen for diagnosing lower respiratory tract infections?
a) Saliva
b) Expectorated sputum
c) Bronchoalveolar lavage (BAL)
d) Nasopharyngeal swab - Which factor can lead to false-negative stool culture results for enteric pathogens?
a) Refrigerating the specimen promptly
b) Using Cary-Blair transport medium
c) Collecting after antibiotic therapy
d) Placing the specimen in a sterile container - Why are anticoagulants like EDTA not recommended for blood cultures?
a) They inhibit bacterial growth
b) They promote clot formation
c) They interfere with Gram staining
d) They increase hemolysis - What is the ideal blood-to-broth ratio in a blood culture bottle?
a) 1:1
b) 1:5
c) 1:10
d) 1:100 - Which action is essential to avoid contamination during urine culture collection?
a) Collecting the first portion of urine stream
b) Using a clean-catch midstream technique
c) Storing the specimen at room temperature overnight
d) Collecting in a non-sterile container - In suspected cases of fungal bloodstream infections, which factor improves recovery rate?
a) Smaller blood volume per bottle
b) Use of mycobacterial broth medium
c) Use of lysis-centrifugation method
d) Use of anaerobic media only - When collecting stool for Clostridium difficile toxin testing, the specimen should be:
a) Collected in a preservative
b) Refrigerated immediately if delayed testing
c) Mixed with saline solution
d) Left at room temperature for 24 hours - What is the main reason for collecting multiple sets of blood cultures in suspected bacteremia?
a) To detect contamination
b) To identify antibiotic resistance
c) To increase sensitivity and detect intermittent bacteremia
d) To reduce costs of laboratory testing
- Which type of container is inappropriate for viral specimen collection?
a) Sterile screw-cap container with viral transport medium
b) Dry sterile swab
c) Swab placed in universal transport medium
d) Cryovial stored at 2–8°C - Which type of specimen is not suitable for anaerobic culture?
a) Vaginal swab
b) Abscess aspirate
c) Tissue biopsy from deep wound
d) Blood collected in an anaerobic bottle - When collecting blood cultures from pediatric patients, the recommended volume is:
a) 0.5–1 mL per bottle
b) 2–3 mL per bottle
c) 5–10 mL per bottle
d) 20–30 mL per bottle - For which type of specimen is a sterile, wide-mouth container most appropriate?
a) Sputum for culture
b) Blood for culture
c) Tissue biopsy for anaerobic culture
d) Nasopharyngeal swab for viruses - What is the preferred transport condition for viral swab specimens?
a) Frozen at –20°C immediately
b) Refrigerated at 2–8°C in viral transport medium
c) Stored at room temperature
d) Dried on a slide and sealed - Which step is most important in reducing false-negative results in urine cultures?
a) Use of boric acid preservative
b) Collecting the last portion of urine
c) Prolonged transport at room temperature
d) Using non-sterile gloves - Which factor can cause false-positive results in stool occult blood testing?
a) Specimen delay of 2 hours
b) Patient on high vitamin C diet
c) Eating red meat before collection
d) Use of Cary-Blair transport medium - Which method is preferred for collecting a specimen from a closed abscess?
a) Swab after incision
b) Needle aspiration using sterile syringe
c) Cotton swab from surrounding tissue
d) Collection of drainage from gauze - Which is the best approach to minimize contamination during blood culture collection?
a) Collecting through a pre-existing IV line
b) Using strict aseptic technique with two antiseptics
c) Warming the patient’s hand before venipuncture
d) Collecting only one blood culture set - A specimen labeled only as “body fluid” should be:
a) Rejected due to improper labeling
b) Processed immediately
c) Sent for routine culture only
d) Stored until source is identified - Which of the following is an unacceptable specimen for blood culture?
a) Blood collected after initiation of antibiotics
b) Blood collected from venipuncture site
c) Blood collected from a sterile syringe directly into culture bottles
d) Blood collected in appropriate volume - Which of the following is not a preanalytic variable affecting microbiology test results?
a) Site selection for specimen collection
b) Method of specimen transport
c) Duration of incubation in the laboratory
d) Timing of specimen collection - For best results, throat cultures for suspected diphtheria should be:
a) Collected after initiation of antibiotics
b) Collected with a sterile swab and transported immediately
c) Stored at room temperature for 12 hours
d) Collected in a dry container without transport medium - What is the primary reason for using transport media in microbiology specimen handling?
a) To sterilize the specimen
b) To promote rapid bacterial growth
c) To preserve organism viability without allowing multiplication
d) To eliminate contaminants - Why is timing of blood culture collection important in suspected septicemia?
a) To avoid hemolysis of the specimen
b) To collect during fever spikes for maximum yield
c) To reduce the number of bottles used
d) To prevent overgrowth of contaminants - Which step is critical when collecting catheter tip specimens for culture?
a) Place tip in formalin solution
b) Collect only if catheter is removed aseptically
c) Store at room temperature for 24 hours before processing
d) Use a dry, unsterile container - What is the maximum time delay acceptable for cerebrospinal fluid (CSF) specimens before processing for culture?
a) 15 minutes
b) 1 hour
c) 4 hours refrigerated
d) Immediate processing is required - Which of the following may lead to rejection of a wound specimen?
a) Sample collected using a sterile needle and syringe
b) Sample submitted as a dry swab with no information on wound type or site
c) Sample transported within 30 minutes
d) Sample placed in anaerobic transport medium - What is the ideal transport temperature for stool specimens for enteric pathogens?
a) Frozen immediately
b) Refrigerated at 2–8°C if delayed
c) Incubated at 37°C
d) Stored at room temperature indefinitely - Which precaution is essential when collecting specimens for viral cultures?
a) Use of non-sterile containers
b) Avoiding swabs with wooden shafts and cotton tips
c) Collecting after antiviral therapy has begun
d) Transporting dry swabs without medium - Why is it necessary to collect multiple stool specimens on separate days for parasite detection?
a) Parasite shedding may be intermittent
b) To reduce culture costs
c) To increase bacterial overgrowth
d) To obtain larger specimen volume - What is the proper blood-to-broth ratio for blood cultures to reduce antibacterial effects in adults?
a) 1:2
b) 1:3
c) 1:10
d) 1:30 - What is the best method to collect urine from a patient with an indwelling catheter?
a) Remove catheter, cut tip, and submit
b) Disconnect catheter from bag, collect urine aseptically
c) Collect urine directly from drainage bag
d) Aspirate urine aseptically from catheter tubing - Which specimens are acceptable for anaerobic culture?
a) Vaginal swab, eye swab
b) Intraoral surface swab, leg tissue
c) Pleural fluid, brain abscess fluid
d) Urine, sputum - Why is sodium polyanetholsulfonate (SPS) used in blood cultures?
a) Inactivates penicillin/cephalosporins
b) Prevents RBC clumping
c) Inactivates neutrophils and serum complement
d) Facilitates anaerobe growth - What is optimal for anaerobic culture from a wound?
a) Swab before antibiotics
b) Swab after antibiotics
c) Syringe with pus before antibiotics
d) Syringe with pus after antibiotics - What is the most critical factor in recovering organisms in bacteremia?
a) Subculture bottles at day 5
b) Recommended blood volume cultured
c) Daily blood cultures for 3 days
d) Multiple sets from one venipuncture - What should virus transport medium contain?
a) Agents for rapid viral growth
b) Inhibitors of bacterial/fungal growth
c) Agents to destroy nonpathogenic viruses
d) Inhibitors of complement-fixing antibodies - How should a bronchoscopy sample for Legionella be plated?
a) Thiosulfate citrate bile salt media
b) Incubate anaerobically
c) Reject specimen, request sputum
d) Buffered charcoal yeast extract agar with antibiotics - Which medium should be added to stool cultures after flooding?
a) Colistin nalidixic acid for Listeria
b) MacConkey with sorbitol for Campylobacter
c) Mannitol salt agar for Enterococcus
d) TCBS for Vibrio - What media should a male urethral discharge be inoculated to?
a) Blood and phenylethyl alcohol agars
b) EMB and blood agars
c) Thioglycolate broth and chocolate agar
d) Chocolate and modified Thayer-Martin agars - Which medium isolates gram-positive bacteria?
a) Columbia CNA with sheep blood
b) Trypticase soy agar with sheep blood
c) Eosin methylene blue
d) Modified Thayer-Martin - What is required for Campylobacter jejuni isolation from feces?
a) Inoculate selective media, incubate reduced O₂ + CO₂ at 42°C
b) Store in tryptic soy broth before plating
c) Inoculate selective media, incubate at 35°C and room temp
d) Incubate in Cary-Blair media before plating. - Which specimen request is acceptable?
a) Feces for anaerobic culture
b) Foley tip for aerobic culture
c) Rectal swab for gonococci smear
d) Urine for acid-fast bacilli culture - A sputum Gram stain shows many squamous cells (>25/lpf) and mixed flora. What does this indicate?
a) Pneumococcal pneumonia
b) Anaerobic infection
c) Haemophilus pneumonia
d) Oropharyngeal flora - Why might neutrophil nuclei appear dark blue in a Gram stain?
a) Iodine omitted
b) Inadequate decolorization
c) Smear too thin
d) Normal staining - What is the key difference between Ziehl-Neelsen and Kinyoun acid-fast stains?
a) Dye type
b) Microscope used
c) Acid decolorizer strength
d) Use of heat for dye penetration
Answer Key
Answer Key:
- b) Proper specimen collection and handling
- b) Immediately, kept at room temperature
- b) Amies transport medium with charcoal
- c) To avoid suppression of bacterial growth
- b) Aspirate collected into a sterile syringe
- c) Specimen containing >10 squamous epithelial cells per low-power field
- a) Boric acid
- b) Improper site disinfection before collection
- c) Cerebrospinal fluid for bacterial culture
- b) Povidone-iodine followed by alcohol
- b) 5–10 mL
- a) Collection after initiation of antibiotics
- b) Sterile, oxygen-free transport vial
- b) Rayon or Dacron
- d) Both “Death and distortion of trophozoites” and “Increased bacterial overgrowth”
- b) Specimen transported after 24 hours at room temperature
- c) Swab from a superficial wound exposed to air
- c) Contamination with skin flora during collection
- b) It is the most common colonization site
- a) Cary-Blair medium
- b) 2 hours
- c) Bronchoalveolar lavage (BAL)
- c) Collecting after antibiotic therapy
- a) They inhibit bacterial growth
- c) 1:10
- b) Using a clean-catch midstream technique
- c) Use of lysis-centrifugation method
- b) Refrigerated immediately if delayed testing
- c) To increase sensitivity and detect intermittent bacteremia
- b) Dry sterile swab
- a) Vaginal swab
- b) 2–3 mL per bottle
- a) Sputum for culture
- b) Refrigerated at 2–8°C in viral transport medium
- a) Use of boric acid preservative
- c) Eating red meat before collection
- b) Needle aspiration using sterile syringe
- b) Using strict aseptic technique with two antiseptics
- a) Rejected due to improper labeling
- a) Blood collected after initiation of antibiotics
- c) Duration of incubation in the laboratory
- b) Collected with a sterile swab and transported immediately
- c) To preserve organism viability without allowing multiplication
- b) To collect during fever spikes for maximum yield
- b) Collect only if catheter is removed aseptically
- d) Immediate processing is required
- b) Sample submitted as a dry swab with no information on wound type or site
- b) Refrigerated at 2–8°C if delayed
- b) Avoiding swabs with wooden shafts and cotton tips
- a) Parasite shedding may be intermittent
- c) 1:10
- d) Aspirate urine aseptically from catheter tubing
- c) Pleural fluid, brain abscess fluid
- c) Inactivates neutrophils and serum complement
- c) Syringe with pus before antibiotics
- b) Recommended blood volume cultured
- b) Inhibitors of bacterial/fungal growth
- d) Buffered charcoal yeast extract agar with antibiotics
- d) TCBS for Vibrio
- d) Chocolate and modified Thayer-Martin agars
- a) Columbia CNA with sheep blood
- a) Inoculate selective media, incubate reduced O₂ + CO₂ at 42°C
- d) Urine for acid-fast bacilli culture
- d) Oropharyngeal flora
- b) Inadequate decolorization
- d) Use of heat for dye penetration
Top 8 Medical Laboratory Scientist (MLS) Exams:
Top 8 Medical Laboratory Scientist (MLS) Exams that are recognized globally and can help professionals validate their credentials and enhance their career opportunities:
1. ASCP – American Society for Clinical Pathology (USA)
- Exam Name: MLS(ASCP)
- Eligibility: Bachelor’s degree with clinical laboratory experience.
- Global Recognition: High
- Purpose: Certifies Medical Laboratory Scientists in the United States and internationally.
2. AMT – American Medical Technologists (USA)
- Exam Name: MLT(AMT) or MT(AMT)
- Eligibility: Academic and/or work experience in medical laboratory technology.
- Global Recognition: Moderate
- Purpose: Credentialing for medical technologists and technicians.
3. AIMS – Australian Institute of Medical and Clinical Scientists
- Exam Name: AIMS Certification Exam
- Eligibility: Assessment of qualifications and work experience.
- Recognition: Required for practice in Australia.
- Purpose: Certification and registration in Australia.
4. CSMLS – Canadian Society for Medical Laboratory Science
- Exam Name: CSMLS General or Subject-specific Exams
- Eligibility: Graduation from a CSMLS-accredited program or equivalent.
- Recognition: Canada
- Purpose: Entry-to-practice certification in Canada.
5. IBMS – Institute of Biomedical Science (UK)
- Exam Name: Registration and Specialist Portfolio Assessment
- Eligibility: Accredited degree and lab experience.
- Recognition: UK and some Commonwealth countries.
- Purpose: Biomedical Scientist registration with the HCPC (UK).
6. HAAD / DOH – Department of Health, Abu Dhabi (UAE)
- Exam Name: DOH/HAAD License Exam
- Eligibility: Degree in medical laboratory science and experience.
- Recognition: UAE (Abu Dhabi)
- Purpose: Licensure for medical laboratory practice in Abu Dhabi.
7. DHA – Dubai Health Authority (UAE)
- Exam Name: DHA License Exam for Medical Laboratory Technologists
- Eligibility: Relevant degree and experience.
- Recognition: Dubai, UAE
- Purpose: Professional license for clinical laboratory practice in Dubai.
8. MOH – Ministry of Health (Gulf Countries like UAE, Saudi Arabia, Kuwait)
- Exam Name: MOH License Exam
- Eligibility: BSc/Diploma in Medical Laboratory + experience.
- Recognition: Varies by country.
- Purpose: Required for practicing in public and private sector labs.
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