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UW Health SMPH
American Family Children's Hospital

UW Hospital and Clinics Lab Test Directory

Test Name: PTT

Test Code(s): APTT / PTT

CPT Code(s): 85730

Methodology: Mechanical Clot Detection

Days Performed: Daily, 24 hours.

Turnaround Time: Stat: 1 hour.
Routine: 4 hours.

Specimen Requirements

Specimen: Blood

Collection Instructions: The venipuncture MUST be atraumatic to avoid hemolysis and contamination with tissue factors and platelets. Tube MUST be allowed to fill up to "fill" line indicated on tube. Do not spin or open.

If unable to collect 1.8 ml tube (pediatrics only) please call Core Coagulation Lab at 263-9617 or Special Coagulation Lab at 263-5005 for alternate tube and instructions.

Collection Container: Preferred: Light blue top (3.2% NaCitrate)

Collection Volume: Preferred: 3.5 mL
Pediatrics: 1.8 mL

Sample Analyzed: Plasma

Volume Required: Preferred: 0.5 mL
Pediatrics: 0.5 mL

Specimen Processing: Centrifuge specimen to yield platelet poor plasma (platelet count should be less than 10 K/uL). Separate plasma and transfer to plastic tube or vial. Freeze plasma at -20C or below.

Specimen Transport: Transport whole blood specimen at room temperature to UWHC Core Laboratory (B4/220) within 4 hours of collection. Otherwise, transport frozen plasma aliquot on dry ice to UWHC Core Laboratory (B4/220).

Unacceptable Criteria: Hemolyzed specimens, clotted specimens, partially filled tubes and whole blood specimens greater than 4 hours old when received by the laboratory are not acceptable.

Stability: Ambient: 4 hours
Refrigerated: Not acceptable
Frozen: 2 weeks at -20C; 6 months at -70C


Reference Interval:


 0 days - 4 days:  28.0-50.0 seconds
 5 days - 29 days:  22.0-50.0 seconds
 30 days - 6 months:  24.0-38.0 seconds
 7 months and up:  26.0-35.0 seconds

Critical Calls: View

Additional Information:

See UWHC Pharmacy therapeutic heparin dosing guidelines.

PTT APTT Activated Partial Thromboplastin Time

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