2016 L1 Intro to Biochem

Specimen Blood Collection Tubes and order of Draw

1. PALE YELLOW, for blood culture + culture media, must draw first, use sterile techniques

2. LIGHT BLUE, for coagulation studies + sodium citrate, invert 4 times

3. RED, for chemistry + get serum separator clot activator, invert 5 times

4. GOLD YELLOW, for chemistry + heparin, invert 8 times

5. PURPLE, for hematology + EDTA, invert 10 times

6. PINK, for blood group cross matching + EDTA, invert 8 timees

7. BLACK, for blood glucose + potassium oxalate and sodium fluoride, invert 10 times

Heparin

• Anticoagulant

• Used in clinical biochem

• Mucoitin polysulfuric acid (available as sodium, potassium, ammonium or lithium salts)

• PRevents formation of fibrin from fibrinogen

• Expensive

EDTA

• Anticoagulant

• Chelating agent, binds Ca necessary for clotting

• Inhibits alkaline phosphatase

• Used for Haemoglobin A1c (monitoring diabetes)

Citrate

Anticoagulant, used for coagulation studies

Fluoride Oxalate

• Anticoagulant

• Preservative of choice for glucose analysis

• Inhibits glycolysis

Urine Collection

• Random sample, qualitative - collected at unspecified time, used for drug abuse screening

• 24h Collection, quantitative - eliminates variations due to diurnal variation

• Used for protein excretion, electrolytes and creatinine

• Creatinine/albumin ratio - compromise between random and timed specimens

• Urine preservatives - added to reduce bacterial growth, chemical decomp, precipitation of constituents

Problems with Specimen Collection

• Poor sampling techniques, e.g. haemolysis - release of potassium and other RBC constituents

• Prolonged stasis during venepuncture - plasma water diffuses into interstitial spaces, protein-bound constituents falsely elevated

• Insufficient samples

• Errors in timing

• Incorrect specimen containers

• Inappropriate sample site e.g. IV

• Incorrect storage e.g. stored overnight before sending to lab by GP

Accuracy

• Form of analytical variation, how close is it to true answer

• Uses reference material with known values

• Percentage deviation known as bias, can be pos or neg

Accuracy Variation

Interferences

• Haemolysis

• Lipaemia

• Icterus

• Hyperproteinaemia

• Drugs

Precision

• Form of analytical precision, replicability

• CV used as a measure

IQC samples

• Internal quality control, for monitoring performance of each method

• Have known concentrations

• Measured several times a day

• Variation in results reflect imprecision

• Differences from target value indicate accuracy