Improving Consultative
Feel of the Laboratory:
Adding Post-Analytical
Comments to Your Reports
Paul C. Schreckenberger, Ph.D., D(ABMM), F(AAM)
Professor of Pathology
Director, Clinical Microbiology Laboratory
Loyola University Medical Center
Pschrecken@lumc.edu
Herbert M. Sommers, M.D.
2
Financial Disclosures
3
Objectives
• Develop strategies for optimal laboratory
testing with the goal of eliminating
unnecessary and inappropriate test methods
• Identify opportunities to improve physician
understanding of laboratory results issued by
their own laboratory
• List specific post-analytic comments used in
microbiology to clarify relevance and
significance of microbiology results
4
Evidence Based Medicine
• Using objective scientific data to
make a clinical diagnosis or predict
the success of a specific treatment
• Based on accurate reproducible
test results and proven clinical
outcomes
5
Evidence Based Medicine
• Does a Physician have the right to
expect that the laboratory results
are accurate, significant and
clinically relevant?
• If the answer is YES, then where
should we begin?
6
Evidence Based Medicine
• Should begin by acting as consultants,
not just someone who provides a
service
– We are physicians, doctoral scientists,
microbiologists, technologist…… not just
laboratory people
7
Evidence Based Medicine
The Clinical Laboratory
Phases of Diagnostic Testing
Preanalytical

Patient Assessment
Test Request
Specimen Collection
Specimen Transport
Specimen Receipt
Specimen Processing
Analytical 
Testing
Quality Control
Verification
Postanalytical
Result Reporting
Result Interpretation
Post-test Specimen
Management
8
Specimen Selection
Things we can say “no” to:
 Sputum (based on stain)
 Endotracheal (based on stain)
 Routine Throat cultures
 Routine Vaginal cultures
 Urine (based on UA)
 Wounds (based on stain)
 Sterile Fluids, AFB sent on
swabs
 Stool (>3 days)
 Stool for fungus
 C. difficile on formed stool
 C. diff as test of cure
 CSF for fungi and TB
 Direct Agn tests on CSF
 >3 blood cultures in 24h
9
Impact of Specimen Management
• Key to accurate laboratory diagnosis
• Affects patient care and patient outcomes
• Influences therapeutic decisions
• Impacts hospital infection control
• Impacts patient length of stay, hospital
costs and laboratory costs
• Influences laboratory efficiency
10
Impact of Specimen Management
• Not just trying to get out of doing things,
we are trying to help physicians help
their patients
– Rules for acceptance and work up of
specimens are good for the patient
11
Pre-Analytical Assessment
Specimen Collection
• Recovery of microorganisms is directly related to
specimen quantity
• Collect as much specimen as possible
• DON’T USE SWABS! (exceptions:
throat; nasopharyngeal; cervical/vaginal)
• Use syringes to aspirate fluid and scalpels for
tissue
12
Pre-Analytical Comment
Patient Report
• Test Requested: AFB Culture
• Specimen: Swab
• Result: “Test cancelled: swab
specimens are inappropriate for AFB
culture. Appropriate specimens
include; body fluids (min. vol. 3-10
ml), respiratory secretions (min. vol.
3-10 ml), and tissue.”
13
Post Analytical Comment
Patient Report
• Tissue, needle aspirates, and ….
swabs
• We perform culture if specimen
acceptable and another specimen not
easily obtainable
• Add disclaimer to final report:
“Specimen received on swab. Results may
not be reliable. For maximum sensitivity
submit, tissue, fluid, or needle aspirate.”
• Good idea for a QA monitor
14
CSF Cultures for AFB/Fungus
• RULE: Screen all CSF requests from adults
Fungus and AFB testing not performed if:
- Clear CSF
- WBC less than 5 x 106 cells/L
- Glucose >3.3 mmol/L (60 mg/dL)
• Unused fluid frozen in original sterile vial.
Stored 30 days. Laboratory performs testing
if physician then requests testing
– Albright RE et al: AJCP 95:418-423, 1991
– Bromberg K: Lancet 1:1023, 1980
– Crowson TW et al: JAMA 251:70-72, 1984
15
Pre-Analytical Assessment
Patient Report - LUMC
• “Test Cancelled: CSF Fungus and AFB
cultures are only performed if cellular or
chemical abnormalities are present in the
CSF. Specific test was not performed
because analysis of this sample revealed
glucose >55 mg/dL and WBC <5 cells/uL.
If consultation is required, page the
microbiology laboratory director (12504).”
16
Screening Criteria for HSV PCR
• RULE: Screen all CSF HSV PCR requests
Test performed only if:
- Patient with HIV
- Patient with history of transplant
- An age of <2 years
- CSF WBC count >5 cells/mm3
- CSF protein >50 mg/dl
17
Screening Criteria for HSV PCR
• Unused fluid frozen in original sterile vial.
Stored 30 days. Laboratory performs
testing if physician then requests testing.
– Hanson KE et al. Validation of laboratory screening
criteria for herpes simplex virus testing of
cerebrospinal fluid.
J Clin Microbiol. 2007 Mar;45(3):721-4.
– Ihekwaba UK et al. Clinical features of viral
meningitis in adults: significant differences in CSF
among HSV, VZV and EV infections.
Clin Infect Dis. 2008 Sep 15;47(6):783-9
18
Screening Sputum
• RULE: perform Gram stain and evaluate
under LPF (10 x). Reject if >10
SEC/LPF, unless also see a predominant
field of WBCs assoc. with single
morphotype of bacteria
• Ref:
– Murray PR, Washington II JA: Mayo Clinic Proc.
50:339-344, 1975
– Wong LK et al: JCM 16:627-631, 1982
19
20
Pre-Analytical Comment
Screening Sputum
• Cancel Culture, Charge for Gram
Stain only
• DON’T REQUEST REPEAT
CULTURE: Add Comment:
“specimen contaminated with
epithelial cells represents
oropharyngeal contamination further
processing would yield potentially
misleading results.”
21
Screening Endotrachs
• RULE: specimens with >10 SEC/LPF,
or no organisms seen on Gram stain
(or yeast only) are not cultured
• References:
–
–
–
–
Morris AJ et al: JCM 31:1027, 1993
Zaidi AK, Reller LB : JCM 34:352, 1996
Rand KH: Diagn Micro Infect Dis 27:55, 1997
Gilligan PH: Clin Micro Newsl 21:44, 1999
22
Stool Cultures
• RULE: Restrict culture and O & P exam
to outpatients and inpatients admitted
<3 days
• RULE: Reject fungal culture on stools.
Add statement: “Fungal cultures of stool
have not been shown to be clinically
useful.”
• Reference:
– Hines J, et al: Clin Infect Dis 23:1292, 1996
23
Post-Analytical Comment
Comment for E. coli 0157:H7
24
Post Analytical Comment
Comment for E. coli 0157:H7
25
Post Analytical Comment
Comment for E. coli 0157:H7
• “Antimicrobial agents should not routinely be
used to treat gastroenteritis due to E. coli
0157:H7 because they may increase the risk
of hemolytic uremic syndrome.”
– Wong CS et al: The risk of the hemolytic-uremic syndrome
after antibiotic treatment of Escherichia coli O157:H7
infections. N Engl J Med. 2000 Jun 29;342(26):1930-6.
– Cieslak PR, Swerdlow DL: Escherichia coli O157:H7: What
the Clinician Needs to Know. Infect Dis Clin Pract 4(2):123127, March/April 1995
26
Guidelines for Submitting C. difficile
• Test only when following criteria are met:
1. Antibiotic within 2 mos. prior to diarrhea
2. Diarrhea water/profuse: 6 episodes in 36h
3. Absence of other diagnosis for diarrhea
• Test only fresh diarrheal stools, no swabs
• Do not test asymptomatic patients and
young children
–Cohen SH, et al. Infect Control Hosp Epidemiol. 2010 May;31(5):431-55.
*Shea Position Paper
27
Guidelines for Submitting C. difficile
• Infants and children
– Neonates (< 6 weeks) and infants < 2 yrs may have
toxin-producing strains in stool but are asymptomatic
– Colonization of neonates occurs within a few days of
birth usually from environmental sources rather than
maternal
– Prevalence of C. difficile carrier state in healthy,
asymptomatic infants < 18 mos. as high as 70%
– Children > 2 yrs. epidemiology similar to adults
McGowan KL: Clin Micro Newsl 21:49-53, 1999
Cerquetti M et al: Pediatr Infect Dis J 14:598-603, 1995
28
Clinical Practice Guidelines for CDI in
Adults: 2010 Update by SHEA/IDSA
• First update of guidelines originally published in ICHE
in 1995
• Literature reviewed from 1994 through April 2009
• Panel
of experts met face-to-face and via
conference calls
• Strength of evidence and quality of recommendations
were based on Canadian Task Force (CMAJ 1979)
• Document underwent external & internal review with
final approval by SHEA and IDSA Boards of Directors
Cohen SH et al. Infect Cont Hosp Epidemiol 2010;31:431-55
29
Diagnosis Recommendations
•
•
•
.. the sensitivity and specificity of a stool culture and
identification of a toxigenic isolate (i.e. toxigenic
culture) .. provides the standard against which other
clinical test results should be compared (B-III)
EIA testing for toxin A and B is rapid but is less
sensitive than the cell cytotoxin assay and is thus ..
sub-optimal .. (B-II)
.. One potential strategy is a two-step method using
EIA or GDH as an initial screen and the cell cytotoxicity
assay or toxigenic culture as the confirmatory test on
GDH positive stools .. (B-II)
Cohen SH et al. Infect Cont Hosp Epidemiol 2010;31:431-55
30
2-Step Testing Caveats
• Rationale for 2-step strategy predicated on
GDH as a sensitive screening test
• Sensitivity range: 71% to 89%
Ribes J et al. ICAAC-IDSA. 2008;
Washington, DC. Abstract D-2277 (84 to
87%)
Broeck JV et al. ECCMID. 2009; Helsinki,
Finland. Abstract P-1169 (71 to 89%)
31
Diagnosis Recommendations, cont.
•
PCR testing appears to be rapid, sensitive and
specific and may ultimately address testing
concerns. More data needed .. (B-II)
•
Repeat testing during the same episode of
diarrhea is of limited value and should be
discouraged (B-II)
Cohen SH et al. Infect Cont Hosp Epidemiol 2010;31:431-55
32
Results of Xpert C. difficile Clinical
Trial Data
• A total of 2296 patient samples from seven sites
tested by Xpert C. difficile assay, enriched
anaerobic culture and toxin testing, and the sites’
standard of care
Tenover FC et al. J Clin Microbiol. 2010
Oct;48(10):3719-24
33
Sensitivity of Xpert C. difficile and other methods
compared to enriched toxigenic culture
Sensitivity
Xpert
Site
Specificity
Xpert
Site
PPVa
Xpert
Site
NPVa
Site
N
Site Assay
Xpert
1
1023
Toxin A/B EIA
94.1% 67.5% 93.7% 92.0% 74.6% 62.6% 98.8% 93.5%
2
268
GDH-EIA
91.4% 74.3% 93.6% 94.8% 68.1% 68.4% 98.6% 96.1%
3
293
Toxin A/B EIA
92.3% 53.8% 94.5% 97.6% 72.0% 77.8% 98.8% 93.2%
4
312
Toxin A/B EIA
91.4% 54.3% 94.2% 95.7% 66.7% 61.3% 98.9% 94.3%
5
114
GDH-EIA-PCR 92.3% 69.2% 96.0% 97.0% 75.0% 75.0% 99.0% 96.1%
6
173
Toxin A/B EIA
97.0% 33.3% 93.6% 93.6% 78.0% 55.0% 99.2% 85.6%
7
110
Cytotoxin
90.9% 54.5% 94.9% 98.0% 66.7% 75.0% 98.9% 95.1%
Tenover FC et al. J Clin Microbiol. 2010
Oct;48(10):3719-24
Site
34
Ability of Xpert C. difficile versus EIA to
Identify Specific Ribotypes
Xpert C. difficile
Positive Negative
Enzyme Immunoassay
Ribotype
n
Sensitivity Positive Negative
(%)
Sensitivity
(%)
P value
001
8
8
0
100
6
2
75.0
0.46
002
13
13
0
100
2
11
15.4
<0.0001
017
11
10
1
90.9
7
4
63.6
0.311
027
74
74
0
100
58
16
78.4
<0.0001
053
12
12
0
100
8
4
66.7
0.093
078
11
9
2
81.8
7
4
63.6
0.635
104
6
5
1
83.3
3
3
50.0
0.545
106
16
12
4
75.0
3
13
18.8
0.004
Tenover FC et al. J Clin Microbiol. 2010
Oct;48(10):3719-24
35
36
Post-Analytical Comment
Clostridium difficile
• Hard stool: “Testing for Clostridium difficile
toxin is not performed on this stool sample
because it is solid (not diarrheal). Treatment
for Clostridium difficile toxin is not
recommended for asymptomatic carriers (i.e.
patients without diarrhea). If this patient was
previously positive, 10% of patients will
remain positive for weeks to months in spite
of resolution of symptoms. Test-of-cure is not
recommended.”
–Cohen SH, et al. Infect Control Hosp Epidemiol. 2010 May;31(5):431-55.
37
Post-Analytical Comment
Clostridium difficile
• Children < 2 years old:
“Clostridium difficile toxin testing not
performed on children under 2 years of age.”
– Cohen SH, Gerding DN, Johnson S, Kelly CP, Loo
VG, McDonald LC, Pepin J, Wilcox MH. Clinical
practice guidelines for Clostridium difficile infection
in adults: 2010 update by the society for
healthcare epidemiology of America (SHEA) and
the infectious diseases society of America (IDSA).
Infect Control Hosp Epidemiol. 2010
May;31(5):431-55.
38
Wound Culture-Work up
• Priority List-Potential Pathogens
– Staphylococcus aureus
– Beta Streptococcus
– Pseudomonas aeruginosa
• Predominant morphyotype associated with
PMNs
• Specific organisms based on patient condition
or type wound eg. Bite
• Apply Rule of three
39
Culture work-up
“The number of species found in a clinical
specimen is in some way indirectly
proportional to the patient care value of
the report”
- Ray Bartlett, M.D.
40
Culture work-up: Rule of Three
• RULE: Do not work up culture when 3
or more pathogens are present with no
single pathogen present as the
predominant organism
• REPORT AS: “mixed flora consisting of
(enter no.) Gram-positive and (enter no.)
Gram-negative organisms.”
41
Diabetic Foot Ulcers
• Plantar ulcers associated with diabetes
mellitus
• Inability of PMNs to kill organisms
• Foot infection diagnosed primarily on clinical
grounds
• Most important pathogens
– S. aureus
– beta streptococci,
– P. aeruginosa
42
Post-Analytical Comment
Patient Report - Wound
• Always look for and report S. aureus,
Beta Strep, P. aeruginosa, pure culture
GNB otherwise report as:
“mixed flora consisting of (enter no.)
Gram-positive and (enter no.) Gramnegative organisms. Culture negative
for Staphylococcus aureus, Beta
Streptococcus and Pseudomonas
aeruginosa”
43
Post-Analytical Comment
Blood Cultures
• Only 1 culture obtained:
“In order to evaluate possible skin
contamination and to ensure
adequate volume of blood sampled, 2
separate venipunctures are
recommended for blood culture.”
44
Post-Analytical Comment
Blood Cultures
• Less than 5 ml of blood in bottle:
“Less than 5 ml of blood received in
one or both blood culture bottles.
Optimal recovery of pathogens
requires 8-10 ml per bottle.”
45
Post-Analytical Comment
Blood Cultures
• Greater than 3 blood cultures ordered/24
hour period: “Test cancelled: Nearly all
positives detected by 3 sets”
• Nearly all episodes of bacteremia and
fungemia in adult patients are detected with
2-3 blood cultures.
– Wilson, M. L. Clinically Relevant, Cost-Effective Clinical
Microbiology. Am J Clin Pathol. 1997 Feb;107(2):154-67.
Review.
– Principles and Procedures for Blood Cultures; Approved
Guideline. CLSI document M47-A. Wayne, PA: Clinical and
Laboratory Standards Institute; 2007.
46
Post-Analytical Comment
Blood Cultures
• Contamination Comment: Added for
following organism types: Coag Neg Staph,
Viridans Strep, Corynebacterium, Bacillus
spp., Micrococcus, Lactobacillus, Rothia
mucilaginosa, Propionibacterium whenever
isolated from single blood culture set or when
isolated from multiple sets from different days
that are separated by negative blood culture
sets. “Coagulase negative Staph isolated
from a single set of blood cultures. This
suggests probable skin contamination. No
further work up.” or
47
Post-Analytical Comment
Blood Cultures
• “Susceptibility will not be performed
because clinical significance of
coagulase negative Staphylococci
isolated from a single blood culture
is undetermined. Please consult
Microbiology if further work-up is
needed.”
48
Catheter Tip Cultures
• “No clinical significance has been
established for the use of catheter tip
cultures in the absence of
concomitant positive blood cultures.”
– O’Grady NP et. al. 2002. Clin Infect Dis 35:1281-307
– Mermel L.A. et al. Clinical practice guidelines for the diagnosis
and management of intravascular catheter-related infection:
2009 Update by the Infectious Diseases Society of America.
Clin Infect Dis. 2009 Jul 1;49(1):1-45.
– Widmer, A.F., M. Nettleman, K. Flint, and R.P. Wenzel. 1992.
Clinical impact of culturing central venous catheters. Arch Intern
Med. 152:1299-1302.
49
Catheter Tip Cultures
• Perform quantitative cultures only.
Qualitative catheter tip cultures, have
minimal value as predictors of
bacteremia
• Do not work up if concurrent blood
culture not submitted within 24 h.
Report: “Catheter tip culture in the
absence of concurrent blood culture has
no clinical relevance”
50
Catheter Tip Cultures
• Do not work up unless companion blood
culture is positive, then give descriptive
ID only, perform ID/AST from significant
blood culture isolates
• References:
Nahass RG, Weinstein MP: DMID 13:223, 1990
Widmer AF, et al. Arch Int Med 152:1299, 1992
Peacock SJ, et al. J Hosp Infect 40:35, 1998
51
"Insanity is doing the
same thing over and over
again and expecting a
different result”
Albert Einstein