Sampling body fluids Flashcards
A history of pathology based on the 5 senses
- Sight – Injury, infections, swellings, gangrene
- Touch – Fevers, chills, sensitive areas
- Hearing – Respiratory distress
- Smell – Gangrene, infection, ketones
- Taste – Diabetes mellitus
Ancient Greeks- 4 humous
17th Century
• William Harvey – Human Circulation
18th Century
• Improved knowledge of anatomy
19th Century
• Florence Nightingale and Joseph Lister
Discovery that blood values of many parameters reflected physiological state of patient
Sample pathway
- Pre-analytical
Collecting, labelling, transport
Sample pathway
- Pre-analytical
Collecting, labelling, transport
- Analytical
Diagnostic testing
- Post-analytical
Result reporting, sample storage
What are the common sites for phlebotomy?
- Median Cubital Vein
- Cephalic Vein
- Back of Hand
- Finger prick
- Heel prick
Describe phlebotomy
More than just collecting blood
- Variety of diagnostic tests and analytes measured
- Range of sample collection tubes
- Different sample collecting requirements o Sent on ice? o Protected from light?
What do you need for phlebotomy?
- Vacuum filled tubes
- Adapter
- Gloves
- Tourniquet
- Alcohol wipes
- Adhesive tape
- Gauze
- Sharps bin
Correct sampling
Incorrect sampling
Incorrect sampling
Medical biochemistry test per day (by sample type)
Sample collection:
Patient identification
- Full name and DOB
- Confirm ID
- ID bracelet
Sample collection: Request form
- Filled in correctly
- Appropriate tests requested
- Select required tubes
Sample collection:
Select site for venepuncture
- Bruising? Scar tissue?
- Clean skin
- All consumables ready?
- Need to re-bleed?
Sample collection: Label tubes
- Clinic or patient bedside
- Matching identifiers
- Collected all required samples?
- Date and time of collection
Sample collection:
Transport samples
- Invert tube (not shake)
- Urgent?
- Do not delay!
Packaged correctly
Sample collection:
Minimum identifiers
- Full name
- DOB
- NHS number
What is the difference between plasma and serum
Plasma
- Cell-free liquid component of blood
- Treated with anticoagulants
- Centrifuged
Serum
- Cell-free liquid component of blood after coagulation
- Lacks clotting factors such as fibrinogen
- Centruged after coagulation
Yellow top tube
- Serum Separator Tube (SST)
- Inert gel than is denser than serum but less dense than erythrocytes
- Coated with spray coated silica particles
- Most commonly used tube for routine biochemistry e.g. U&E’s, CRP, liver function, creatinine, lipid profile, bone profile
- Invert 5-6 times
Problems with the yellow top
Problems:
- Incomplete barrier formation
- Sampling probe is damaged
- Gel interferes with some drug/endocrine tests
Red top tube
None/Coated with silica particles
- Serum obtained following centrifugation
- Used for the measurement of blood where a yellow top is inappropriate
How many types of green top tubes are there?
2
Light green tip tube
Gel
- Anticoagulant: Lithium heparin
- Blood does not clot - Plasma
- Invert 8-10 times
Dark green tube
- No gel - requires plasma separation following centrifugation
- Ammonia, insulin, aluminium
Purple top tube
Anticoagulant: K-EDTA • Whole blood
- HbA1c – Measure of glycaemic control for diabetics (reflects control of diabetes)
- Cyclosporin and Tacrolimus (anti-rejection drugs)
- Venous carboxyhaemoglobin
- Invert 8-10 times
Purple top tube
Anticoagulant: K-EDTA • Whole blood
- HbA1c – Measure of glycaemic control for diabetics (reflects control of diabetes)
- Cyclosporin and Tacrolimus (anti-rejection drugs)
- Venous carboxyhaemoglobin
- Invert 8-10 times
Light grey top
Anticoagulant: Potassium Oxalate
- Sodium Fluoride: Inhibits glycolysis (5 days) and alcohol dehydrogenase
- Glucose
- Lactate
- Invert 8-10 times
Dark blue top
Purified glass (no contaminating trace metals)
- Copper
- Zinc
- Mercury
- Selenium
Why is the order of draw important?
Risk of carryover
True or False: SST must be taken before K-EDTA tube
TRUE
- K-EDTA chelates calcium
- Increases potassium
- Artificial hypocalcaemia
- Hyperkalaemia
Interference: Samples require visual inspection prior to analysis
HILREF
Haemolysed samples
- Shaking or expelling blood through a needle
- ↑ potassium, phosphate, AST, LDH and Mg2+
- Colorimetric assay interference
Icteric samples
- Bilirubin peak absorbance at 460nm
- Enzyme activity assays
Lipaemic samples
• Interfere with most assays
Haemolysed Sample Audit
- Prevents tests being performed, misleading results can be reported
- Laboratory data for 7 days: • A&E: 24%
- Inpatients: 2.9%
Haemolysed Sample Audit: In A&E
- Non-standard techniques
- Range of staff
- Drawing blood through fine lines or needles e.g. 20 G cannula and syringing blood into tubes with the needle still on
- Wrong order of draw
Improvements
Use of standard techniques
- Improved training for junior doctors
- Teach order of draw
- Use of vacutainers
- Additional studies regarding the use of fine gauge cannulas and haemolysis
Sample acceptance criteria:
Sample acceptance criteria
- Minimum number of matching identifiers?
- Correct sample tubes for tests requested?
- Adequate sample volume?
- What to do if samples are not received correctly
- How are rejected samples reported?
Urines
- 24 hour urine
- Urinary electrolytes
- Creatinine
- Copper
- Albumin
- Cortisol
- Protein
- Random urine
- Bence Jones Proteins
- Osmolality
- Albumin:Creatinine
Sweat
- Collected non-invasively
- Determine chloride concentration
- Diagnostic for cystic fibrosis
- CFTR mutation screen
