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Clinical Biochem > Clinical Biochem Lab > Flashcards

Clinical Biochem Lab Flashcards

1
Q

What are the traditional divisions of a pathology department?

A
  • microbiology
  • haematology
  • histopathology
  • clinical biochem
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2
Q

Function of a biochem lab

A
  • to diagnose & monitor disease
  • perform tests on specimens to obtain info on the health of a patient
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3
Q

What are some examples of staff in a biochem lab?

A
  • consultant clinical biochemist
  • clinical biochemist
  • biomedical scientist
  • medical lab assistants
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4
Q

Describe the Specimen Reception

A
  • samples may arrive via courier
  • some labs receive them via pneumatic tube systems –> this isn’t suitable for all sample types
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5
Q

What are the 3 point of ID on a sample?

A
  • name
  • D.O.B
  • NHS number
  • hospital number
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6
Q

What happens when a sample fits the specimen reception criteria ?

A
  • its processed
  • logged onto the hospital computer system
  • given a specific lab number
  • allocated appropriate tests
  • labelled & stored immediately
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7
Q

What happens if a sample doesn’t have the 3 point of ID?

A

they are discarded

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8
Q

How is a EDTA blood sample processed?

A
  • 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
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9
Q

What are the plasma ammonia reference range for infants ?

A

< 40 u mol/L

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10
Q

what is the plasma ammonia reference range for adults ?

A

11 - 32 u mol/L

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11
Q

How are blood spot cards processed in the lab?

A
  • sent from babies 5-8 days old - part of newborn screening program
  • only analysed in specialist labs
    -proccessed by MLA
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12
Q

What does the newborn screening/ blood spot card test for ?

A
  • phenylketonuria
  • congenital hypothyroidism
  • sickle cell
  • cystic fibrosis
  • MCADD
  • MSUD
  • IVA
  • homocytinuria
  • GA1
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13
Q

Describe Phenylketonuria (PKU)

A
  • 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
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14
Q

What does phenylketonuria result from ?

A

it results from a deficiency in the enzyme phenylalanine hydroxylase

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15
Q

What effect does phenylketonuria have?

A
  • high phenylalanine (Phe) & low tyrosine level
    -Phe impairs amino acid transport into the brain & impart white matter development
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16
Q

Where are international accreditation standards outlined ?

A

ISO/IEC 15189

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17
Q

What governs all accreditation of labs in the UK?

A

UKAS
UK Accreditation Service

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18
Q

Define Measurement Uncertainty

A

variability in the assay, factors influence assay performance

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19
Q

What are 2 ways QC,s can be made?

A
  • ‘In house’ = internal QC
  • provided by an external agency such as ‘NEQAS’ = external QC
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20
Q

What do QC’s ensure?

A

that analytical methods are accurate, reliable, reproducible & comparable with other labs

21
Q

Define pre-analytical errors

A
  • errors that occur before the sample is analysed
  • factors that can affect results include; sample collection, sampling time, sampling handling & transport
22
Q

Define Sample

A

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

23
Q

What are some examples of Biochemical testing?

A
  • lipid, diabetic, kidney, liver, bone, electrolyte profiles
  • tissue enzymatic activity determinations
24
Q

Describe a Lab Request Form

A
  • contains a list of tests to be performed on specimen of patient
  • each lab has its specific request–> example chemistry request or haematology request
25
Q

Describe a lab report form

A
  • contains the results of a patient
26
Q

Describe the life of a clinical sample

A
  • pre-analytical = test ordering, specimen collection, handling, transport & processing
  • analytical testing = assaying the sample
  • post-analytical = testing results transmission, interrelation, follow-up and retesting
26
Q

Describe the correct process for sample collection

A
  • 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
27
Q

Describe the process of selecting a vein

A
  • vein used to collect blood via venepuncture procedure
  • meidan cubital vein is best choic
28
Q

When is arterial blood collected?

A
  • used in special cases as when blood gases, pH, PCO2, PO2 or bicarbonate is requested
29
Q

Describe the postural effects on drawing blood

A
  • 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
30
Q

What qualifies as an unsatisfactory specimen ?

A
  • 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
31
Q

What is a common cause & consequences of haemolysis

A

causes
- over vigorous mixing of specimen
- excessive delay in transit
- storing specimen in freezer

consequence
- increased K+, bilirubin, LDH
- Decreased Na+, Cl-, Glu

32
Q

What are the causes & consequences of an inappropriate sampling site?

A

cause = specimen taken from drip arm
consequences = increased drip analyte & dilution effect

33
Q

Why is order of the drawer important ?

A
  • done to avoid cross-contamination & unreliable test results
34
Q

What is the correct order of the drawer?

A
  1. blood culture tube (yellow closure)
  2. sodium citrate tube (blue closure)
  3. serum tubes, with clot activator/gels (red closure)
    4.heparin tube with/without gel (green closure)
  4. EDTA tube with/without gel separator(lavender/pink closure)
  5. sodium fluoride/potassium oxalate glycolytic inhibitor (grey closure)
35
Q

Describe testing on whole blood

A
  • 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.
36
Q

What is the difference between serum & plasma ?

A

serum doesn’t contain clotting factors
plasma contains all clotting factors (fibrinogen)
- they share the same contents of electrolytes, enzymes, proteins, hormones

37
Q

How does fibrinogen affect samples?

A
  • absence of fibrinogen would make the supernatant clearer than plasma
38
Q

Describe the preparation of serum

A
  • 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
39
Q

Describe the preparation of plasma

A
  • 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
40
Q

Describe urine collection

A
  • non invasive & readily obtainable
  • more inconvenient than blood collection
  • type of urine selected & collection procedure used to depend on tests performed
41
Q

Describe Urine Analysis

A
  • 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
42
Q

Describe 24 hour urine collection

A
  1. discard 1st sample into toilet, recording on the urine container, the exact time & date the first urine is passed
  2. all urine passed over the next 24hr must be collected in same container
  3. day after you started the collection exactly 24 hrs after 1st collection pass urine to complete collection - record this time & date on container
43
Q

What are some factors that might affect the accuracy of 24hr urine test?

A
  • forgetting to collect some urine
  • going beyond 24hr collection period
    -losing urine due to spillages
  • not keeping urine in a cold place
  • strenuous exercise
44
Q

What are some other forms of urine collection?

A
  • mid stream sample - assess for evidence of infection
  • early morning sample - often best as they’re more concentrated
45
Q

Describe the process of morning urine collection

A
  • 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
46
Q

Describe the sampling process of skeletal muscles

A
  • flash frozen at bedside
  • store at -70
  • transported on dry ice
  • store at -70
  • homogenise
  • freeze thaw x3
  • assay
47
Q

Describe pre-analytical error

A
  • 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

Clinical Biochem (15 decks)

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