Clinical Biochem Lab Flashcards
What are the traditional divisions of a pathology department?
- microbiology
- haematology
- histopathology
- clinical biochem
Function of a biochem lab
- to diagnose & monitor disease
- perform tests on specimens to obtain info on the health of a patient
What are some examples of staff in a biochem lab?
- consultant clinical biochemist
- clinical biochemist
- biomedical scientist
- medical lab assistants
Describe the Specimen Reception
- samples may arrive via courier
- some labs receive them via pneumatic tube systems –> this isn’t suitable for all sample types
What are the 3 point of ID on a sample?
- name
- D.O.B
- NHS number
- hospital number
What happens when a sample fits the specimen reception criteria ?
- its processed
- logged onto the hospital computer system
- given a specific lab number
- allocated appropriate tests
- labelled & stored immediately
What happens if a sample doesn’t have the 3 point of ID?
they are discarded
How is a EDTA blood sample processed?
- blood sample tube/request sheet is correctly labelled
- test required is plasma ammonia level
- plasma has to be isolated ASAP from RBCs
- once separated plasma is assayed for ammonia determination
What are the plasma ammonia reference range for infants ?
< 40 u mol/L
what is the plasma ammonia reference range for adults ?
11 - 32 u mol/L
How are blood spot cards processed in the lab?
- sent from babies 5-8 days old - part of newborn screening program
- only analysed in specialist labs
-proccessed by MLA
What does the newborn screening/ blood spot card test for ?
- phenylketonuria
- congenital hypothyroidism
- sickle cell
- cystic fibrosis
- MCADD
- MSUD
- IVA
- homocytinuria
- GA1
Describe Phenylketonuria (PKU)
- affects 1/10,000 Caucasian births
- severe intellectual disability if untreated
- excellent prognosis if treated from birth - low Phe diet
- screening test = bloodspot phenylalanine
- ref range = 120-360 u mol/L
What does phenylketonuria result from ?
it results from a deficiency in the enzyme phenylalanine hydroxylase
What effect does phenylketonuria have?
- high phenylalanine (Phe) & low tyrosine level
-Phe impairs amino acid transport into the brain & impart white matter development
Where are international accreditation standards outlined ?
ISO/IEC 15189
What governs all accreditation of labs in the UK?
UKAS
UK Accreditation Service
Define Measurement Uncertainty
variability in the assay, factors influence assay performance
What are 2 ways QC,s can be made?
- ‘In house’ = internal QC
- provided by an external agency such as ‘NEQAS’ = external QC
What do QC’s ensure?
that analytical methods are accurate, reliable, reproducible & comparable with other labs
Define pre-analytical errors
- errors that occur before the sample is analysed
- factors that can affect results include; sample collection, sampling time, sampling handling & transport
Define Sample
any biological material taken from a patient for diagnostic, prognostic or therapeutic monitoring under the Human Tissues Act includes;
- blood
- urine
- faeces
- sweat
-semen
-CSF
-tissue like skeletal muscle
What are some examples of Biochemical testing?
- lipid, diabetic, kidney, liver, bone, electrolyte profiles
- tissue enzymatic activity determinations
Describe a Lab Request Form
- contains a list of tests to be performed on specimen of patient
- each lab has its specific request–> example chemistry request or haematology request
Describe a lab report form
- contains the results of a patient
Describe the life of a clinical sample
- pre-analytical = test ordering, specimen collection, handling, transport & processing
- analytical testing = assaying the sample
- post-analytical = testing results transmission, interrelation, follow-up and retesting
Describe the correct process for sample collection
- positively identify the patient
- remember to add the label to sample in presence of patient
- confirm verbally the details with patient
- ensure details are correct
- seal/package the specimen in front of the patient
- send to the lab promptly
Describe the process of selecting a vein
- vein used to collect blood via venepuncture procedure
- meidan cubital vein is best choic
When is arterial blood collected?
- used in special cases as when blood gases, pH, PCO2, PO2 or bicarbonate is requested
Describe the postural effects on drawing blood
- change from supine to sitting causes clinically significant increases in haemoglobin, haemltocrit & red blood cell count
- can also affect the conc. of circulatory lipoproteins, triglycerides
What qualifies as an unsatisfactory specimen ?
- inadequate quantity of blood collected
- improper collection contianer
-clotted specimen - haemolysed or lipaemic samples - lipid content
- too much time elapsed since collection
- transported at inappropriate temperature
What is a common cause & consequences of haemolysis
causes
- over vigorous mixing of specimen
- excessive delay in transit
- storing specimen in freezer
consequence
- increased K+, bilirubin, LDH
- Decreased Na+, Cl-, Glu
What are the causes & consequences of an inappropriate sampling site?
cause = specimen taken from drip arm
consequences = increased drip analyte & dilution effect
Why is order of the drawer important ?
- done to avoid cross-contamination & unreliable test results
What is the correct order of the drawer?
- blood culture tube (yellow closure)
- sodium citrate tube (blue closure)
- serum tubes, with clot activator/gels (red closure)
4.heparin tube with/without gel (green closure) - EDTA tube with/without gel separator(lavender/pink closure)
- sodium fluoride/potassium oxalate glycolytic inhibitor (grey closure)
Describe testing on whole blood
- testing should be performed with limited delay
- overtime cells will lyse in whole blood, which will change the conc. of some analytes such as potassium
- some cellular metabolic processes will continue which will alter analytes conc.
What is the difference between serum & plasma ?
serum doesn’t contain clotting factors
plasma contains all clotting factors (fibrinogen)
- they share the same contents of electrolytes, enzymes, proteins, hormones
How does fibrinogen affect samples?
- absence of fibrinogen would make the supernatant clearer than plasma
Describe the preparation of serum
- draw blood from patient
- select vacutainer with no anticoagulant
-allow to stand for 20-30 for clot formation
-once clot retracts - centrifuge sample, cells & clot will move to bottom & serum is found in upper layer - supernatant is the serum which can now be collected
- stored -20- -80 for subsequent analysis
Describe the preparation of plasma
- draw blood from patient - select vacutainer with an appropriate anticoagulant
- mix well with anticoagulant
- allow to stand for 10 mins
- centrfuge sample
- supernatant is the plasma which can be now collected for testing purpose or stored -20 - -80 for subsequent testing or use
Describe urine collection
- non invasive & readily obtainable
- more inconvenient than blood collection
- type of urine selected & collection procedure used to depend on tests performed
Describe Urine Analysis
- clean & dry plastic or glass containers
- preservative may be needed depending on assay
- total volume must be recorded
- specimen must be recorded
- aliquots for specific assays
Describe 24 hour urine collection
- discard 1st sample into toilet, recording on the urine container, the exact time & date the first urine is passed
- all urine passed over the next 24hr must be collected in same container
- day after you started the collection exactly 24 hrs after 1st collection pass urine to complete collection - record this time & date on container
What are some factors that might affect the accuracy of 24hr urine test?
- forgetting to collect some urine
- going beyond 24hr collection period
-losing urine due to spillages - not keeping urine in a cold place
- strenuous exercise
What are some other forms of urine collection?
- mid stream sample - assess for evidence of infection
- early morning sample - often best as they’re more concentrated
Describe the process of morning urine collection
- subject voids before going to sleep & immediately upon rising, collects a urine specimen
- specimen must be preserved if not delivered within 2 hours of collection
- can be used to isolate cells from urinary tract & used for determination of mitochondrial DNA & enzymes
Describe the sampling process of skeletal muscles
- flash frozen at bedside
- store at -70
- transported on dry ice
- store at -70
- homogenise
- freeze thaw x3
- assay
Describe pre-analytical error
- generally out of the control of the labratory
- sample taken inappropriately
- stored & transported at incorrect temperatures
- insufficient material
- assocaited with 70% of all errors in a diagnostic sample
