MT 116: LEC 4 - Specimen Collection, Handling, and Processing

Clinical Chemistry

What is the most common specimen in clinical chemistry?

Blood

Which blood vessels have thick walls and carry oxygenated blood?

Arteries

Which blood vessels have thin walls and carry deoxygenated blood?

Veins

Which blood vessels are only one cell thick to allow gas and nutrient exchange?

Capillaries

How much blood does an average adult have?

5–6 liters (7–8% body weight)

What percentage of blood is formed elements?

45%

What percentage of blood is fluid portion?

55%

What is the difference between plasma and serum?

Plasma = with fibrinogen (anticoagulated); Serum = without fibrinogen (after clotting).

What is the main difference between arteries and veins in terms of pressure?

Arteries = high pressure; Veins = low pressure

What is the most common specimen in clinical chemistry?

Serum

How long should serum be allowed to clot before centrifugation?

20 minutes

Why should serum/plasma be separated quickly from cells?

To prevent continued metabolism (e.g., glucose consumption) and false results.

What is the first step in specimen collection?

Proper patient identification

How should you identify a conscious inpatient?

Ask full name + verify ID bracelet

What must you do before collecting from a sleeping patient?

Wake them up

How are unconscious/mentally incompetent patients identified?

Ask nurse/relative or check ID bracelet

Who usually confirms the identity of infants/children?

Parent, guardian, nurse, or ID bracelet

How are outpatients identified?

Ask full name, DOB, address + verify with photo ID

What is arterial puncture mainly used for?

Blood gas analysis and pH measurement

What test must be done before radial artery puncture?

Modified Allen test

Which artery is large and easy to puncture but bleeds more, especially in elderly?

Femoral artery

Why is arterial bleeding dangerous?

It is the hardest to control

What are the 3 major complications of arterial puncture?

Thrombosis, hemorrhage, infection (THI)

Name sites to avoid for arterial puncture.

Irritated, edematous, near wounds, or in an area with AV shunt/fistula

What is the most preferred vein for venipuncture?

Median cubital vein

Why should basilic vein be avoided if possible?

It is close to nerves and artery → higher risk of injury.

Why avoid blood collection from edematous areas?

Dilution of specimen → false low results.

Why avoid venipuncture on mastectomy side?

Risk of infection (lymph nodes removed).

What should be done if venipuncture accidentally hits an artery?

Apply pressure immediately and report to supervisor.

In which patients is ankle/foot venipuncture contraindicated?

Diabetic patients (poor circulation, delayed healing).

What is the main purpose of antiseptics in venipuncture?

To prevent sepsis by reducing microorganisms at puncture site.

What is the most commonly used antiseptic in routine venipuncture?

70% ethyl alcohol

Which antiseptic is used for blood culture collection instead of routine venipuncture?

Povidone-iodine (or tincture of iodine).

Why isn’t povidone-iodine used for routine blood collection?

It can interfere with chemistry test results.

What is the main use of sterile gauze pads after venipuncture?

To apply pressure and stop bleeding at the puncture site.

When should a sterile gauze pad be applied?

Immediately after removing the needle.

What complication does pressing with gauze help prevent?

Hematoma formation.

What is the purpose of a tourniquet in venipuncture?

To obstruct venous return and make veins distend for easier puncture.

How far above the puncture site should a tourniquet be tied?

3–4 inches above.

What are the standard dimensions of a tourniquet?

Length ~20 inches, width 1–2 inches, thickness ~1 mm.

Should tourniquets be reused?

Recommended to discard after each phlebotomy, but may be reused with disinfection in practice.

What is the standard needle gauge for routine adult venipuncture?

21 gauge

How does gauge number relate to needle size?

Larger gauge = smaller bore

What gauge is commonly used for children?

23 gauge

What is the insertion angle for venipuncture (exam answer)?

15°

What is the usual length of butterfly needles?

½ – ¾ inch

What are the three main components of a syringe system?

Plastic syringe, needle, transfer device.

When is the syringe method most commonly used?

For patients with small, fragile, or damaged veins (pediatric/geriatric).

Which part of the syringe shows the first backflow of blood?

The hub.

What creates the negative pressure that draws blood into the syringe?

Pulling the plunger.

What type of system is the evacuated tube system?

Closed system.

What automatically determines the volume of blood collected in ETS tubes?

The premeasured vacuum in the tube.

What prevents blood from leaking before the tube is inserted?

The rubber sleeve.

What are the three basic components of ETS?

Special blood-drawing needle, tube holder, evacuated tubes.

How are ETS tube stoppers identified?

By color-coding (additive, no additive, or special property).

What does the color of an evacuated tube stopper indicate?

The presence/absence of an additive and the type of additive.

Why are color codes important in evacuated tubes?

They guide which tube to use for specific laboratory tests.

What do some tubes contain aside from anticoagulants?

Clot activators or no additive at all.

What does the butterfly system look like?

A short needle with plastic wings and tubing.

Which patients is the butterfly system mainly used for?

Pediatric and geriatric patients with fragile veins.

What are the wings of the butterfly system for?

To help secure the needle during venipuncture.

When should a bandage be applied after venipuncture?

After the bleeding has stopped.

What is the purpose of applying a bandage?

To protect the puncture site and prevent infection.

What are the two main ways anticoagulants prevent clotting?

By removing calcium or inhibiting thrombin formation.

Why is calcium important in blood clotting?

It is required for normal coagulation.

What do evacuated tubes with anticoagulants prevent?

Blood clotting.

What is the anticoagulant of choice for hematology cell counts?

EDTA.

How does EDTA prevent blood from clotting?

By chelating calcium.

What is the optimal concentration of EDTA?

1.5 mg/mL of blood.

In which tube is EDTA commonly found?

Lavender-top tube.

What happens if there is excess EDTA in the sample?

Cells shrink.

What is the anticoagulant used in coagulation studies?

Sodium citrate.

What color tube contains sodium citrate?

Light blue top.

How does sodium citrate prevent clotting?

By chelating calcium.

What is the standard blood-to-citrate ratio?

9:1.

Name two concentrations of sodium citrate.

3.2% and 3.8%.

What tube color is used for heparin?

Green-top tube.

How does heparin prevent coagulation?

By accelerating antithrombin III, which neutralizes thrombin and prevents fibrin formation.

Why is heparin preferred for potassium tests?

It preserves cell integrity.

Which type of heparin cannot be used for sodium assays?

Sodium heparin.

Which type of heparin is used for most chemistry tests?

Lithium heparin.

How do oxalates prevent coagulation?

By precipitating calcium.

What is the most widely used oxalate?

Potassium oxalate.

Which tube color usually contains oxalates?

Gray-top tube.

How many inversions are required for proper mixing with oxalates?

8–10 inversions.

What happens if oxalate tubes are overfilled?

Excess oxalate causes hemolysis and releases hemoglobin into plasma.

What is ACD mainly used for?

DNA testing and HLA phenotyping.

How does ACD prevent coagulation?

By binding calcium.

What anticoagulant is used for blood transfusion collection?

Citrate Phosphate Dextrose (CPD).

Which anticoagulant is used in blood cultures?

Sodium Polyanethol Sulfonate (SPS).

What color tube stopper do ACD and SPS share?

Yellow.

How many inversions are required for ACD and SPS tubes?

8 inversions.

What is the function of an antiglycolytic agent?

Prevents glycolysis (glucose breakdown).

How much does glucose decrease per hour if glycolysis is not prevented?

About 10 mg/dL per hour.

Which conditions have faster glycolysis?

Newborns and leukemia patients.

What is the most common antiglycolytic agent?

Sodium fluoride (NaF).

What tube color is associated with antiglycolytic agents?

Gray-top tubes.

Sodium fluoride is commonly paired with what anticoagulant?

Potassium oxalate.

What is the role of clot activators?

To enhance coagulation for faster serum specimen preparation.

Give 2 examples of clot activators.

Silica particles and thrombin.