Transcript Introduction to Laboratory Medicine

Introduction to Laboratory
Medicine
Roger L. Bertholf, Ph.D.
Some SHJ Lab Statistics
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Number of employees: 130
Number of tests/year: 1.5 million
Yearly budget: $16 million
Yearly revenue: $70 million
– Net $25 million
Laboratory organization
• Core Laboratory (73% of volume)
– Chemistry, hematology, toxicology, immunochemistry, special chemistry, coagulation,
urinalysis
• Microbiology (16 % of volume)
– Blood/urine cultures, serology
• Transfusion Services (3% of volume)
– Blood typing and cross-matching
Chemistry
• Electrolytes, glu, BUN, creat, phos, TP, Bili, Mg,
Ca, cholesterol, triglycerides, etc.
• Blood gases: pO2, pCO2, pH, calc. Parameters
• Immunochemistry: endocrine, specific protein,
tumor markers
• Toxicology: DAU, TDM
• Urinalysis
• Special Chemistry: electrophoresis, L/S ratio, FLM,
osmometry
SHJ Chemistry Instruments
• Roche/Hitachi Modular and 914
– Chemistries and homogeneous immunoassays
• Roche Elecsys 2010
– Heterogeneous immunoassays
• NOVA M (whole blood gas/electrolytes)
• Abbott IMx
• Yellow Iris
Hematology
• CBC/Diff
• Coagulation
• Microscopy
SHJ Hematology Instruments
• Abbott Cell Dyne 4000
– CBC, Auto differential
• Organon Technika MDA
– Coagulation
Microbiology
• Cultures
– Blood
– Urine
– Sputum, wound, etc.
• Antibiotic sensitivity
• Serology
– Viral Ab, Ag testing
Point of Care Testing
• Instruments are available that can perform certain
tests at remote locations, such as at the bedside on
in a clinical care unit
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Blood glucose
Urinalysis
Blood gases
Electrolytes/BUN/Creatinine
Cardiac markers (Troponin I & T, CK-MB)
Coagulation (ACT)
• POC tests are nearly always more expensive, than
the same tests performed in the central laboratory
POCT at SHJ
• Blood glucose (Not under lab license)
• Electrolytes on the GEM Premier in the OR
• ACT in the OR and Cardiac Catheterization
Lab
• Urinalysis (not under lab license)
Reasons for POC testing
• Tests are of urgent importance, and results
will affect the immediate management of
the patient
– Blood gases, electrolytes
• Tests are so common, simple and cheap that
it is more economical to perform them at
the point of care
– Blood glucose, urinalysis
SHJ Blood Gas Lab
• Operated by Respiratory Therapy
• Performs blood gases and whole blood
electrolytes/BUN/Creatinine/Glucose
– Gases fall under RT license
– Chemistries fall under the lab license
• Serves MICU, CCU, PICU, NICU, SICU
• Performs all co-oximetry
Steps in obtaining a laboratory test
1.
2.
3.
4.
5.
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7.
8.
Written order is placed
Specimen is collected and properly labeled
Specimen and order are transported to the lab
The specimen is accessioned in the lab
The specimen is processed
The specimen is analyzed
The results are reviewed and verified by an MT
The results are released to the patient’s record
How long steps 4-7 take (P1 orders)
45
40
35
Minutes
30
Mean
25th %ile
50th %ile
75th %ile
25
20
15
10
5
0
Q1
Q2
How long steps 4-7 take (STAT)
60
50
40
Mean
25th %ile
50th %ile
75th %ile
% >1 hr
30
20
10
0
Q1
Q2
Sources of error in laboratory results
• Pre-analytical
• Analytical
• Post-analytical
Pre-analytical errors
• Collection
– Was the right tube used?
– Was venipuncture performed correctly?
– Was the specimen properly stored?
• Identification
– Was the blood collected from the correct
patient?
– Was the blood correctly labeled?
• Patient name, ID, date, time of collection,
phlebotomist
Collection tubes
• Red-top tubes contain no anticoagulants or
preservatives
• Red-top tubes are used for collecting serum
– 10-15 minutes is required to allow blood to clot
before centrifuging
– Used for blood bank specimens, some
chemistries
Collection tubes
• Gold (and “tiger”) top tubes contain a gel
that forms a physical barrier between the
serum and cells after centrifugation
• No other additives are present
• Gel barrier may affect some lab tests
Collection tubes
• Gray-top tubes contain either:
– Sodium fluoride and potassium oxalate, or
– Sodium iodoacetate
• Both perservatives stabilize glucose in plasma
– NaF/oxalate inhibits enolase
– Iodoacetate inhibits glucose-3-phosphate
dehydrogenase
Collection tubes
• Green-top tubes contain either the sodium
or lithium salt of heparin
– The amount of Na+ or Li+ is insignificant
• Heparin inhibits thrombin, so blood does
not clot (plasma)
• The advantage of plasma is that no time is
wasted waiting for the specimen to clot
Collection tubes
• Lavender-top tubes contain EDTA, which
chelates calcium and inhibits coagulation
• Used for hematology, and some chemistries
Collection tubes
• Blue-top tubes contain sodium citrate,
which chelates calcium and inhibits
coagulation
• The blood/anticoagulant ratio must be
precisely known, since the tubes are used
for coagulation studies.
Collection tubes
• Brown and Royal Blue top tubes are
specially cleaned for trace metal studies
– Brown-top tubes are used for Pb analysis
– Royal blue-top tubes are used for other trace
element studies (acid washed)
Plasma/Serum differences
• Plasma concentration greater than serum:
– Ca (+0.9%), LD (+2.7%), TP (+4.0%)
• Plasma concentration less than serum:
– Alb (-1.3%), ALKP (-1.6%), HCO3- (-1.8%),
CK (-2.1%), PO4= (-7.0%), K+ (-8.4%)
Prolonged venous stasis
• Increases TP, Fe, cholesterol, AST, bilirubin
• Decreases potassium
Supine vs. sitting or standing
• The following may decrease by 5-15% in the
supine patient:
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Total protein
Albumin
Lipids
Iron
Calcium
Enzymes
Ig
Thyroxine
Significantly affected by hemolysis:
• Total protein, albumin, lipids, iron, calcium,
enzymes, bilirubn, cholesterol, triglycerides,
norepinephrine, renin, aldosterone,
potassium, magnesium, phosphorous
Specimens requiring special handling
• Should be placed immediately on ice
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Lactate
Ammonia
Acid phosphatase
Plasma catecholamines
Exertion-related changes
• Recent strenuous exercise increases:
– Acid phosphatase, ALT, AST, creatinine,
phosphorous, CK
• Recent strenuous exercise decreases:
– Iron, lipids, potassium
Other factors affecting lab results
• Diurnal variations
– Cortisol, iron, estriol, glucose, catecholamines
• Age
– Creatinine, BUN, ALKP, drug metabolism
• Smoking
– Ammonia, CO-Hb
Specimen identification
• One of the commonest sources of erroneous
lab results is misidentified specimens
• CAP and other accrediting agencies require
the lab to have a clear and rational policy
for identifying specimens, and handling
misidentified specimens
• The blood bank has stricter requirements for
specimen identification
Misidentified specimens at SHJ
29: Delay in obtaining lab results
26: Specimen collected/labeled/registered with wrong patient
46: Specimen unlabeled/mislabeled/labeled incompletely
Number of citations
140
120
100
Q1 2000
Q2 2000
Q3 2000
Q4 2000
Q1 2001
Q2 2001
80
60
40
20
0
Total
29
26/26A/26B
RAQ indicator
46