Clinical Chemistry Week 2

Stages of Specimen Testing

• Pre-analytical

• Analytical

• Post-analytical

Pre-analytical Phase

• Collection

• Transportation

• Handling

• Processing

Specimen Requisitions

• Can be paper (requisition) or electronic (LIS)

• Sample label cross checked with requisition

• 3 ID

• Patient name, DOB, Hospital ID/MRN

• Patient location in/outpatient

• Physicians name/address/phone number

• Specimen prioritization (STAT) or other (fasting)

• Patient history (if any)

• Tests to be performed

• Signature/initials of who drew the blood, date+time

STAT

• short for statum in latin: immediate

• Shor Turn Around Time

• takes priority over almost anything your are doing

• Guidelines: not always reasonable/feasible 

• Life/Death situations

Urgent/ASAP

• Looking for results soon

• process sample right away

• finish what you are doing then process sample

Routine

• Processed with next batch

• general TAT targets

Timed Samples

• Some samples need to be collected at specific time intervals

• ie. drugs; Therapeutic Drug Monitoring: scheduled dosing and half-life tested

• Fasting 8/12h

• ie. glucose, cholesterol, triglycerides

Plasma

• Treated with anticoagulants

• Cell free-liquid after spun down

• Has clotting factors

Serum

• Liquid after coagulated blood is spun down

• no clotting factors

Whole Blood

• Used for blood gases

Other Types of Samples

• Urine

• Stool

• CSF

• Other fluids

Green Top Tubes

• Na/Li Heparin

• may be SST

Gray Top

• Potassium oxalate + Sodium fluoride

• used when testing can’t happen immediately

• preserves glucose, ethanol (sensitive to metabolism and evaporation)

• see in private labs or transferred

Red Top

• No anticoagulant

• clot activator

Tiger Top/Gold Top SST

• Gel moves between cells and serum

Check Tube after Requisition

• Expiry of tube

• Venous blood/other sample

• Correct fill

• Correct anticoagulant

• Correct transportation:

• time collected vs time received (some tests are time sensitive

• Correct temperature: some analytes degrade quickly cold:(blood gases, ammonia) warm: (cold agglutinins)

• Protected from light: some analytes degrade in the presence of light (bilirubin, Vitamin B12)

Sample Separation

• Cells should be separated within 2h

• Do not refrigerate gel separator tube before spinning

• Can’t spin serum samples too soon (after 30 min)

Aliquots

• when multiple tests requested for a single specimen

• Must be labeled with same ID info as specimen tube

• Certain analytes must be frozen immediately after separation

Sample Separation: Centrifugation

Stopper:

• reduce evaporation

• prevent aerosol formation

• Maintain anaerobic conditions: calcium and co2

Specimen Integrity

• inspect and note serum/plasma for HIL index

• note on requisition with results

• depends on analyte/analyzer/method

• may require recollection

Specimen Integrity: Hemolysis

• Intravascular (in vitro)

• Hemolytic Anemia

• Transfusion Reaction

• Extravascular

• Vigorous mixing

• Difficult draw

• Errors in venipuncture: prolonged tourniquet, site selection, venous trauma, wrong needle gauge

• Old sample

• Analytes affected: potassium phosphate, LDH

Specimen Integrity: Lipemic Sample

• High concentration of fat/lipid in serum/plasma

• associated with some diseases

• can be due to a fatty meal (cholesterol/triglyceride test done fasting)

• Interfere with test/analyzers that use optical methods

Specimen Integrity: Icteric Samples

• Serum/plasma is bright yellow-dark yellow instead of straw yellow

• high bilirubin (patient is jaundiced)

• End product of hemoglobin break down

• produced in the liver and excreted in urine and feces

• hepatitis, cirrhosis, newborns with low liver function

• May interfere with analysis measured at same wavelength (400-540nm)

• Some colour reagents may react 

Sample Storage

• Serum/Plasma stable for 24-72h at RT

• Specimens not being run should be capped and refrigerated within 8h

• Most samples stored at 2-8 C post analysis (another test requested, repeat test)

• stored for few days to longer

Sample Storage: Freezer

• Serum/plasma that need to be stored longer, frozen at -20 C

• stored upright, tightly secured

• Some analytes need to be frozen

• Do not store in frost-free freezer

• temperature fluctuations

• avoid repeated freeze/thaw cycles (degrade analytes)