WEEK 3: LAB DIAGNOSIS: FROM SPECIMEN COLLECTION TO DIAGNOSIS Flashcards
A patient’s specimen is a ‘reflection of the patient’s condition at the time of collection’. Maintaining quality/integrity of specimens is vital for accurate laboratory diagnosis results.
What does Successful collection depend on?
Successful collection depends on:
*Collection at appropriate time
*Use of correct technique
*Use of correct equipment
*Safe & timely delivery to lab
What is the health care practitioner’s role in specimen collection?
Health care practitioner’s role:
-Know requirement(s) for a lab’s investigation
-Initiate the collection procedure
-Collect the required & appropriate clinical specimen into the correct sterile specimen container
-Arrange prompt delivery under optimal conditions to the laboratory
Clinical specimens should be collected ‘before’ antibiotic or antimicrobial treatment.
Why?
When unusual specimens are to be collected double check ‘specific’ laboratory requirements.
There will be few, or no bacteria detected by the tests as there are killed by the antibiotic.
How is the investigation for organ specific disease different from Generalized diseases.
For Generalized diseases, on top of the Radiology and microbiology done in Organ specific diseases, there is need for hematology and chemistry immunology.
Outline specific guidelines & or standards i.e., Occupational health & safety (OSHA) or Centre for Disease & Control (CDC) for specimen collection.
Wear gloves for contact with blood or other potentially infectious materials
If specimens are accidentally touched wash hands immediately
Eating, drinking, smoking, applying make-up prohibited: pathogens can be transmitted hand-to-mouth
No licking of labels that are to be applied to specimen containers
Breaks on skin must be covered with plasters or bandages
Specimen spills on work surfaces must be cleaned with appropriate disinfectants.
State general equipment required for specimen collection.
Disposable gloves
Labelled specimen container
Laboratory request form
Swab in transport medium
Spatula
Sterile water
Needle and syringe
Tourniquet
Many of the
-Chemistry (e.g., blood chemistry),
-Hematology (e.g., full blood count),
-Serology (e.g., immunology: antibody-antigen detection)
lab tests are performed on:
After collection these should be promptly transported to the lab, at what temperature should they be maintained at, and the delivery should be done within how much time?
*Whole blood
*Serum
*Plasma
After collection these should be promptly transported to the lab, maintained at 2-8C & delivered within 2-4 hours.
ATT: whole blood, serum & plasma are not interchangeable matrices for lab tests.
- What is serum?
II. How is it obtained? - What is plasma?
II. How is it obtained?
- Serum: fluid attained after the clotting of whole blood. External to the body, blood clots spontaneously, when it is in contact with a surface e.g., glass or plastic.
Serum is the liquid portion of blood that remains after the blood has clotted and the clot has been removed.
II.Serum is formed by allowing a blood sample to coagulate or clot.
During coagulation, the blood cells, primarily red blood cells, white blood cells, and platelets, become trapped in a fibrin mesh, forming a blood clot. The liquid portion that separates from the clot is serum.
In a lab, the clotted blood is usually centrifuged to sediment the clot (containing the RBC’s) to allow for collection of serum.
- Plasma is the fluid component of blood & is obtained when an anti-coagulant is added to whole blood which is then centrifuged to separate the cellular material from the liquid portion (plasma).
Differentiate between plasma and serum.
- So certain components will not be present in serum in comparison to plasma e.g., WBC’s, RBC’s, fibrinogen, platelets (& other clotting factors) absent in serum but present in plasma.
So certain blood analytes tested for different lab tests will not have the same counts within blood vs. serum vs. plasma.
- The main difference between serum and plasma is that plasma is obtained by anticoagulating the blood sample, preventing it from clotting.
Outline components of serum.
*Water
*Electrolytes (sodium, potassium, calcium, etc.), *Proteins (such as albumin, globulins, and other serum proteins)
*Hormones
*Waste products, and various metabolites.
It is a vital component of the circulatory system and plays a key role in transporting nutrients, hormones, and waste products throughout the body.
What is the color of serum?
How many % of blood is made up by serum?
It is a clear, pale-yellow fluid.
It makes up approximately 55% of total blood volume.
It is important to collect blood in the correct ‘vacutainers’ appropriate for the subsequent tests.
Some analytes do partition freely between the rbc’s & the plasma.
How will counts in blood vs. plasma be?
Ethylene-diamine-tetra acetic acid (EDTA) is used as an anticoagulant added to blood that will be used for several tests. But it is a chelating agent & sequesters metal ion e.g., Ca2+ & Mg2+.
How will counts for these in whole blood vs plasma be?
Why would serum (or plasma attained with a different anticoagulant from EDTA) would be more appropriate for testing for ALP?
Some analytes do partition freely between the rbc’s & the plasma. So counts in blood vs. plasma would be similar e.g. Parathyroid Hormone
Ethylene-diamine-tetra acetic acid (EDTA) is used as an anticoagulant added to blood that will be used for several tests. But it is a chelating agent & sequesters metal ion e.g., Ca2+ & Mg2+. So, counts for these in whole blood vs plasma, will be different.
Also, EDTA inactivates some enzymes that need a metal ion for their activity e.g., the liver enzyme ‘alkaline phosphatase’.
This may interfere with the accuracy of counts, so alternatively serum (or plasma attained with a different anticoagulant) would be more appropriate for testing for ALP.
Different anti-coagulants are used dependent on the test to be done.
What are blood cultures bottles used for?
What do the following tops code for?
Yellow top –
Green top –
Orange top –
Black top –
Silver top –
Blood culture bottles
*Used for collecting blood for microbiological cultures, in cases of suspected bacteremia & septicemia:
Yellow top – pediatric (aerobic bacteria)
Green top – adult (aerobic bacteria)
Orange top – anaerobic bacteria
Black top – mycobacteria
Silver top – mycoplasma
Tubes for blood collection
State the anti-coagulant found in the following tube and the samples they take.
- Gold (also tiger top)
- Red-top tube, plastic or glass
- Lavender/ Purple-top tube
- Grey-top tube
- Light green-top tube
- Dark green-top tube
Gold (also tiger top) top serum separator tube (SST)
Contains silica particles for clot activation & serum gel separator.
For serum collection for various chemistry, serology & immunology tests
- Red-top tube, plastic or glass
No clot activator; no anticoagulants or separator material.
For serum collection, at times preferred to SST tubes because gel separator may interfere with analysis
(for various chemistry, serology & immunology tests) - Lavender/ Purple-top tube
Contains EDTA as an anticoagulant.
Used for most hematology assays. - Grey-top tube
Contains potassium oxalate as an anticoagulant.
Sodium fluoride (to inhibit degradation of glucose in blood)
Used for glucose determination in whole blood (& also lactate - Light green-top tube (lithium heparin)
Contains lithium heparin & gel separator.
Used for plasma determinations in routine chemistry tests (rarely used) - Dark green-top tube (sodium heparin)Contains sodium heparin.
Used for the collection of heparinized plasma or whole blood for special tests i.e., ammonia, insulin, renin.
What are microtainers also called?
Microtainers (pediatric tubes)
To avoid cross-contamination of additives between tubes & altering the chemical composition of the blood, a specific order is used:
*Blood culture bottle
*Coagulation tubes - red top
Describe the Last draw - additive tubes in order.
Last draw - additive tubes in this order:
1. SST /red-grey or gold top (clot activator & gel separator)
2. Dark green top (sodium heparin)
3. Light green top (lithium heparin & gel separator)
4. Lavender top (EDTA)
5. Pale yellow top/ ACD (acid citrate dextrose)
6. Light gray top (Oxalate/fluoride
Why is good aseptic technique imperative?
Good aseptic technique imperative to avoid ‘contamination’, by resident commensal bacteria or bacteria in environment.
*Contaminants may outgrow causative pathogen & falsify test results.
Supplies for specimen collection e.g., swabs & transportation (transport vials) must be sterile.
Clearly labeled: patients’ information, date, source, initials of person collecting
Causative pathogens in clinical specimens can perish in-transit or be masked by the ‘overgrowth’ of contaminants.
State 3 precautions to be taken into account when transporting specimen.
- Clinical specimens should be transported speedily & under optimal conditions to maintain the ‘viability’ of the pathogens.
- Use a leak-proof primary receptacle
Specimen container caps/lids should be securely closed before placing them in the transport carrier. Leaking specimens will not be processed.
- A completed requisition must accompany each specimen.