Clinical Specimen Basics I and II

Question 1

describe the flow of patient’s symptoms –> lab –> potential treatment

Answer 1

Question 2

describe a direct method

Answer 2

culture (look for/detect the agent)

• advantages
  
  • allows anti-microbial susceptibility testing
  • allows typing of the microorganism
  • allows storage of the strain
• disadvantages
  
  • depends upon the viability/condition of the agent
  • turn around time is long

Question 3

describe direct blotting vs. PCR

Answer 3

• direct blotting:
  
  • no amplification (enough DNA)
    
    • DNA of the agent is released
      
      • gets spotted onto a membrane and fixed
      • is recognized by labeled probes (hybridization)
• PCR
  
  • amplification (not enough DNA)
  • rapid, high sensitivity and specificity
  • use in most virology testing

Question 4

describe Ag/Ab testing (indirect method)

Answer 4

detects host response to the agent

• advantages
  
  • inexpensive
  • easy to perform
  • allows identification of
    
    • IgM (acute infxn)
    • IgG (past infxn)
• disadvantages
  
  • delayed response
    
    • false negative results during sero-conversion window
  • time of infection not always clear

Question 5

describe immuno-diagnosis of acute infections

Answer 5

• draw an acute serum
  
  • within 7-14 days
    
    • titers are usually zero or low at <7 days
• draw a convalescent serum 3-6 weeks after the first serum
  
  • look for a 4 fold or greater titer increase due to IgG
    
    • if initial titer is 1:4, the convalescent titer should be 1:16 or greater

Question 6

describe testing for congenital infections

Answer 6

check antibody titer for agents suspected (CMV, Toxoplasma, etc.)

• test at birth (cord blood serum)
• test baby again after 3-4 months
• if baby is negative for infection:
  
  • IgM should NOT be present
  • IgG titer from mother will drop at rate of 50% loss every month and will never go back up
    
    • in 3 or 4 months, the baby titers are low or negative
• baby positive for infection:
  
  • IgM will be positive and IgG titers eventually go up

Question 7

describe interpreting a single, acute IgM test

Answer 7

Question 8

describe interpreting a single, acute IgG test

Answer 8

Question 9

what can you do if you miss the acute titer?

Answer 9

• draw a convalescent titer when titer is high
  
  • 3-6 weeks after the start of the infection
• a very high convalescent titer, and if the clinical symptoms agree, the infection can be presumptively confirmed
  
  • a single positive antibody usually does not allow a definitive confirmation of most acute infxns
  • exceptions are the chronic infxns:
    
    • lyme disease
    • HIV infxn
    • hepatitis infxns

Question 10

describe diagnosis of HIV

Answer 10

• do assays to check for presence of a variety of antibody types to increase test specificity
  
  • tests for a panel of antibodies to surface and internal proteins helps eliminate false positive reactions due to just one or two cross-reacting common antigens between closely related microbes
  • a Western blot procedure is one way to produce a variety of separate antigens from the virus or bacterium of interest so that these antigens can be used to test for distinct antibodies from the patient
  • PCR for nucleic acid

Question 11

describe throat swabs (sampling technique)

Answer 11

• hold tongue away with tongue depressor
• locate areas of inflammation and exudate in posterior pharynx, tonsillar region of throat behind uvula
• avoid swabbing soft palate; do not touch tongue
• rub area back and forth with cotton or Dacron swab

Question 12

describe nasopharyngeal swab (sampling technique)

Answer 12

• tilt head backwards
• insert flexible fine-shafted polyester swab into nostril and back to nasopharynx
• leave in place a few seconds
• withdraw slowly; rotating motion

Question 13

describe sputum (sampling technique)

Answer 13

• instruct patient to take a deep breath and cough up sputum directly in a wide-mouth sterile container
  
  • avoid saliva or postnasal discharge
  • 1 ml minimum volume

Question 14

describe a good sputum sample

Answer 14

Question 15

describe urine sampling

Answer 15

• midstream: clean-catch technique
  
  • clean periurethral area with soap and water
  • pass initial urine into toilet and then collect
  • for: urine culture and other rapid tests
• first catch specimen:
  
  • clean area
  • urine for chlamydia and gonorrhea testing

Question 16

describe sampling catheterized urine

Answer 16

• clean periurethral area with soap and water
• insert catheter into bladder
  
  • discard initial urine
  • collect specimen in sterile cup
• chronic indwelling Foley catheter
  
  • clamp tubing below junction (or port)
  • disinfect with alcohol
  • insert needle (or syringe) through port or catheter wall and aspirate

Question 17

describe suprapubic aspiration

Answer 17

• be certain bladder is full–palpate or percuss
• prep skin with alcohol or iodine
• anesthetize with lidocaine
• introduce needle 2.0 cm above symphysis
• aspirate 20 ml for culture

Question 18

describe a good urine sample

Answer 18

Question 19

describe a bad urine sample

Answer 19

Question 20

do not refrigerate ___ samples

Answer 20

do not refrigerate STD samples

e.g. Neisseria gonorrhea

Question 21

describe sampling a wound specimen

Answer 21

Question 22

describe anaerobic bacterial cultures

Answer 22

Question 23

describe blood cultures

Answer 23

Question 24

describe disinfection of site and recommendations for blood cultures

Answer 24

Question 25

describe a good blood sample

Answer 25

Question 26

you need at least ___ identifiers for labeling specimens

Answer 26

you need at least 2 identifiers for labeling specimens

• patient’s name
• unique ID number
• specimen type
• data, time and place of collection
• name/initials of collector

Question 27

describe transport media

Answer 27

Question 28

describe transport media for anaerobic bacteria and viruses

Answer 28

Question 29

describe ova and parasite exam and transport

Answer 29

Question 30

describe storage of specimens

Answer 30