Les 1 – Laboratory Medicine: clinical biology
Investigated specimens
Almost always biological fluids
• Blood, serum, plasma, urine, cerebrospinal fluid
• Pleural fluid, faeces, saliva…
Purposes of testing
• Screening for disease
In absence of clinical signs/symptoms
• Confirming a clinical suspicion
• Excluding a diagnosis
• Establishing/monitoring the severity of a physiologic disturbance
• Providing a prognosis
• Selection/optimalization/monitoring of treatment
The laboratory testing cycle
Lot of errors during the different phases
→ Sources of error
• Pre-analytical ( 68%)
= patient preparation
o Wrong name of patient
o Erroneous specification of
hospital unit
o Physician’s order missed
o Inappropriate container used
o …
• Analytical (13%)
o Isolated malfunctioning of instrument
o Lack of specificity of the method
o Unacceptable preformance
• Post-analytical (19%)
o Correction of erroneous finding overlooked
o Keyboard entry error
o Turnaround time exceeded
o Physician not notified of problem
Consequences of error
• Incorrect test results
• Incorrect diagnosis
• Unnecessary delays
• Repeated sampling
• Unnecessary cost
1
,Pre-analytical phase
Pre-analytical variation
• Influencing factors
o Lead to changes in the quality of the analyte
o Controllable – non controllable
o Effect may be reduced through standardization of pre-analytical conditions
• Interfering factors
o Mechanisms and factors that lead to falsely increased/decreased results of
laboratory tests
o Differ to intended analyte and analytical method
o May be reduced or eliminated by selecting a more specific method
Influencing factors
Controllable factors:
• Time of sampling
• Influence of diagnostic and therapeutic procedures
o Vein selection
▪ Ante cubital and median cubital veins are most suitable
▪ Use same site to draw serial samples
o Site selection
▪ Avoid intravenous (IV) lines → these are used to deliver fluids
Can cause contamination or dilution
▪ When mastectomy: avoid site due to lymphostatis
Because of infection risk
▪ Avoid edematous areas due to accumulation of body fluids
Contamination possible, dilution
o Tourniquet application
The time of tourniquet application influences the presented quantity of
parameters
o Patient position
Increase (%) in plasma concentration of some analytes when changing from
supine to upright position
o Contrast media
Different media show different presence in parameters
2
,• Diet
o Collection blood after food or beverage intake
▪ Direct effect of hemodilution
▪ Increase of food components (glucose, triglycerides) and their
metabolites
▪ Indirect effect of food components on hormones or other endogenous
compounds
o Important requirement = fasting
o Postpranial state = period immediately after the mail
o Ingestion of food
→ metabolic and hormonal changes due to absorption of fluids, lipids, proteins,
carbohydrates
→ oxidative stress, inflammation, endothelial dysfunction
o Several meals/day → postpranial state predominates
o Need for standardization and harmonisation of fasting requirements for
laboratory tests (+ list of parameters where no fasting is required)
• Fluid intake before sampling
o Water intake
o Alcohol
▪ Increases GGT (liver enzyme), MCV (size rbc) and CDT
o Coffee
▪ Increases fasting blood glucose
▪ Stimulates the adrenal gland: cortisol
• Smoking
o Effects on bloodparameters → some are decreased, some are increased in
smokers vs non-smokers
o Carcinoembryonaal antigen (CEA)
Increased by smokers
o Can lead to abnormalities in form of
neutrophils
• Body position
3
, • Physical activity
o Brief duration and high intensity vs. long duration and lower intensity
o Acute changes: depending on individual and environmental factors
▪ Volume shifts
▪ Volume loss by sweating (electrolytes, proteins, blood count)
▪ Changes in hormone concentration →increased leucocyte conc
o Non-trained person and heavy exercise → muscle breakdown
Uncontrollable factors:
• Age
• Race
• Sex
4
Investigated specimens
Almost always biological fluids
• Blood, serum, plasma, urine, cerebrospinal fluid
• Pleural fluid, faeces, saliva…
Purposes of testing
• Screening for disease
In absence of clinical signs/symptoms
• Confirming a clinical suspicion
• Excluding a diagnosis
• Establishing/monitoring the severity of a physiologic disturbance
• Providing a prognosis
• Selection/optimalization/monitoring of treatment
The laboratory testing cycle
Lot of errors during the different phases
→ Sources of error
• Pre-analytical ( 68%)
= patient preparation
o Wrong name of patient
o Erroneous specification of
hospital unit
o Physician’s order missed
o Inappropriate container used
o …
• Analytical (13%)
o Isolated malfunctioning of instrument
o Lack of specificity of the method
o Unacceptable preformance
• Post-analytical (19%)
o Correction of erroneous finding overlooked
o Keyboard entry error
o Turnaround time exceeded
o Physician not notified of problem
Consequences of error
• Incorrect test results
• Incorrect diagnosis
• Unnecessary delays
• Repeated sampling
• Unnecessary cost
1
,Pre-analytical phase
Pre-analytical variation
• Influencing factors
o Lead to changes in the quality of the analyte
o Controllable – non controllable
o Effect may be reduced through standardization of pre-analytical conditions
• Interfering factors
o Mechanisms and factors that lead to falsely increased/decreased results of
laboratory tests
o Differ to intended analyte and analytical method
o May be reduced or eliminated by selecting a more specific method
Influencing factors
Controllable factors:
• Time of sampling
• Influence of diagnostic and therapeutic procedures
o Vein selection
▪ Ante cubital and median cubital veins are most suitable
▪ Use same site to draw serial samples
o Site selection
▪ Avoid intravenous (IV) lines → these are used to deliver fluids
Can cause contamination or dilution
▪ When mastectomy: avoid site due to lymphostatis
Because of infection risk
▪ Avoid edematous areas due to accumulation of body fluids
Contamination possible, dilution
o Tourniquet application
The time of tourniquet application influences the presented quantity of
parameters
o Patient position
Increase (%) in plasma concentration of some analytes when changing from
supine to upright position
o Contrast media
Different media show different presence in parameters
2
,• Diet
o Collection blood after food or beverage intake
▪ Direct effect of hemodilution
▪ Increase of food components (glucose, triglycerides) and their
metabolites
▪ Indirect effect of food components on hormones or other endogenous
compounds
o Important requirement = fasting
o Postpranial state = period immediately after the mail
o Ingestion of food
→ metabolic and hormonal changes due to absorption of fluids, lipids, proteins,
carbohydrates
→ oxidative stress, inflammation, endothelial dysfunction
o Several meals/day → postpranial state predominates
o Need for standardization and harmonisation of fasting requirements for
laboratory tests (+ list of parameters where no fasting is required)
• Fluid intake before sampling
o Water intake
o Alcohol
▪ Increases GGT (liver enzyme), MCV (size rbc) and CDT
o Coffee
▪ Increases fasting blood glucose
▪ Stimulates the adrenal gland: cortisol
• Smoking
o Effects on bloodparameters → some are decreased, some are increased in
smokers vs non-smokers
o Carcinoembryonaal antigen (CEA)
Increased by smokers
o Can lead to abnormalities in form of
neutrophils
• Body position
3
, • Physical activity
o Brief duration and high intensity vs. long duration and lower intensity
o Acute changes: depending on individual and environmental factors
▪ Volume shifts
▪ Volume loss by sweating (electrolytes, proteins, blood count)
▪ Changes in hormone concentration →increased leucocyte conc
o Non-trained person and heavy exercise → muscle breakdown
Uncontrollable factors:
• Age
• Race
• Sex
4
