Clinical Biochemistry Flashcards
Core Lab
- found at all hospitals
- operates 24/7
- highly automated
Special Chemistry
- less frequent
- labour intensive
- doesnt need immediate results
Point of care testing
- instruments located outside of chemistry laboratory such as ICU, ER etc
Core lab tests
Electrolytes, blood gases, endocrine, lipids, proteins, glucose, tumour markers, vitamins, toxicology, ethanol, methanol, drug abuse, specific proteins etc
Point of care testing tests
- blood glucose
- urinalysis
- blood gases
- electrolytes
- cardiac markers
- drug screens
Why are tests ordered?
- Diagnosis
- Monitor progression of disease
- Monitor effectiveness of treatment
- Screening population for diseases
- To identify complications of treatment
- For predicting survivability, employability
- To check the accuracy of an unexpected data
- To conduct research
- To prevent malpractice
- For educating residents
- To assess nutritional status and health of an health individual
- Responding to total uncertainty
Are cardiac markers and drug screens qualitative or quantitative?
qualitative tests
- can be recorded and reported
Are urinalysis qualitative or quantitative?
can be qualitative, or quantitative
- hard copy of results generated
- possible to interface hospital LIS
High specific marker
troponin t
- marker of myocardial infarction
- found in cardiac tissue
- released into bloodstream following cell death
Non specific marker
low blood pH (acidosis)
- drugs
- respiratory problems
- renal problems
Lab Tests
- Measuring an analyte as a Marker to distinguish health and disease
- Ideal Marker
- Absolutely specific for a specific disease
- Easily measurable
- Quantity reflective of severity of disease
- Early detection following onset of disease
- Not affected by other biological disturbances
Blood analysis- source
- veins
- arteries
- skin puncture capillary blood
Blood analysis- factors affecting choice of blood source and collection method
- analyte under investigation
- vascular status
- ease of collection
Blood analysis- collection method
syringe, evacuated tube, additives, separator gel, and intravenous ilnes
What are the most widely used tubes?
evacuated tubes
Why are evacuated tubes mostly used?
- negative pressure facilitates collection
- sterile
- easy to use
- universally used colour coded rubber stoppers to denote tube type
- tubes can contain various anticoagulants
- tubes can have additives for specific tests
Red tubes
- contain no anticoagulants or preservatives
- used for collecting serum
- 10/15 min is needed to allow blood to clot before centrifuging
- used for blood bank specimens and chemistry
Gold and Tiger tubes
- contain a gel that forms a physical barrier between the serum and cells after centrifugation
- no additives present
- gel barrier can affect tests
Grey tubes
- used for glucose measurement
- after blood collection, glucose concentration decreases significantly because of cellular metabolism
What can the grey tube contain?
- sodium fluoride or potassium oxalate
- sodium iodoacetate
- NaF
- Iodoacetate inhibits glucose-3-phosphate dehydrogenase
Green tubes
- contain either Na, K, or lithium salt of heparin
- used anticoagulant for chemistry test
- effect size and integrity of cellular blood components and not recommended for hematology studies
- heparin accelerates action of antithrombin which inhibits thrombin so blood doesnt clot
Lavender tubes
- contain K salt of ethylenediaminetetraacetic acid (EDTA), which chelates calcium (essential for clot formation) and inhibits coagulation
- Used for hematology, and some chemistries
- Cannot be used for K or Ca tests
Blue tubes
- contain sodium citrate which chelates calcium and inhibits coagulation
- used for coagulation studies because it is easily reversible
Brown and Royal blue tests
- specifically for trace metal studies
- brown top are used for lead analysis
- royal blue are used for other trace elements studies
Test results: variations, errors and interferences
- Clinical variations within an individual and between individuals
- Analytical variations-no test is perfect. All tests have some degree of variations for repeated measurements of the same sample.
- The final test result is affected by factors that occur
- Pre-analytically
- At the time of the test
- After the test is completed
Steps in obtaining a lab test
- Test is requested by physician and ordered on the computer. Barcode is generated
- Specimen is collected
- 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 technologists
- The results are released to the patient’s record
Analytical results vary: inter-individual variation
age, sex, race, genetics, long term health status
Analytical results vary:intra–individual variation
Diet, Exercise, Drugs, Sleep pattern, Posture, Time of venipuncture, and time tourniquet is applied
Analytical results vary: pre analytic variation
- Transport
- Exposure to UV light
- Standing time before separation of cells
- Centrifugation time
- Storage conditions
Analytical Variation
- Random errors
- Systematic errors
Post-analytical
- Transcriptions errors
- Results reported to wrong patient
Pre analytic 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
Specimen identification
- One of the common sources of erroneous lab results is misidentified specimens
- The lab is required to have a clear and rational policy for identifying specimens, and handling misidentified specimens
- Retrievable versus irretrievable
- Retrievable refers to collection of easily obtained substances – eg urine (non-invasive, can get again)
- Irretrievable might be pediatric CSF or even blood (cannot get again)
Prolonged Venous Stasis - pre-analytical errors
- Small molecules, water and ions are forced out blood vessels and larger molecules are concentrated
- Increases Total Protein, proteins, iron, cholesterol, bilirubin
- Decreases potassium
Supine vs sitting or standing
- Going from lying (supine) to upright reduces total blood volume by about 700 ml
The following may decrease by 5-15% in the supine patient:
- Total protein
- Albumin
- Lipids
- Iron
- Calcium
- Enzymes
Hemolysis
- rupture of RBC
- can be due to improper collection
- end result is dumping cellular contents into blood
- mild dilution effect in some analytes
- significant increase in potassium, magnesium and phosphorous
Interferences are
hemolysis and lipemia
Hemolysis interference
- The release of hemoglobin into blood can affect the reactions comprising specific tests
- Causes serum or plasma to be red and can affect tests that are colorimetric
Lipemia
lots of fats and lots of protein
Lipemia interference
- Causes serum or plasma to be become turbid.
- This can effect colorimetric and turbidimetric based tests
- Also can cause a dilution effect. Fats and proteins are large and displace water in plasma. Can give falsely low results especially for Na
