Home
HelpTest Code LAB325 Partial Thromboplastin Time (aPTT)
Performing Laboratory
St. Louis Children's Hospital - Coagulation
Specimen Requirements
Patient Preparation: None
Container/Tube
Preferred: Light blue-top (Citrate) tube (1.8 or 2.7 mL)
Acceptable: Blue-cap (9Cl/1.3) microtainer tube. Call lab at 314-454-4268 if microtainer tube required
Collection Volume: Tube should be full
(Full is to marking on tube label. MINIMUM tube volume for collection is to marking on tube label but may go above line)
Submission Container/Tube: If specimen is coming from outside facility and do not have a STAT spin centrifuge to process, centrifuge and transfer all plasma into a plastic vial, then centrifuge plasma again to get platelet-poor plasma. Aliquot plasma into plastic vial leaving 0.25 mL in the bottom of centrifuged vial. Send to lab STAT
Special Instructions:
|
1. |
Draw a discard tube prior to light-blue top tube. |
|
2. |
Tube(s) should remain stoppered. |
|
3. |
Immediately invert tube/microtainer® gently 8-10 times after collection to ensure proper mixing of blood and anticoagulant (this will avoid specimen clotting). Forward promptly at ambient temperature only. |
|
4. |
DO NOT underfill tube(s) |
|
5. |
SPECIMEN MAY NOT BE COLLECTED BY CAPILLARY METHOD |
|
6. |
If the patient has a known hematocrit >55%, contact the lab at 454-4268 for collection instructions and a specially adjusted collection tube(s). |
Sample Rejection
Vacutainer®(s) that are under-filled.
Clotted specimens.
Grossly hemolyzed specimens.
Mislabeled or unlabeled specimens.
Logistics
Test Availability: Monday-Sunday
Cut-off time: None; performed as received
Turnaround Time: Same day; 1 hours from receipt in performing lab
Reference Values
Reference Interval:
| <1 year: | 25-45 seconds |
| 1 year-10 years: | 25-40 seconds |
| > o r= 10 years: | 26-38 seconds |
| Heparin therapeutic range: 66 -100 seconds. Based on correlation with therapeutic heparin activity range of 0.3-0.7 units/mL | |
Critical Value: >150 seconds
Critical test results will automatically be called back initially and every 72 hours thereafter
Methodology
Absorbance measurement, clot signature formation
Limitations
- NA
Additional Information
FOR SLCH CORE LABORATORY USE ONLY
Lab Processing Instructions: GIve specimen to coagulation bench to be spun in STAT Spin centrifuge for 3 minutes @ 8500 rpm
Processed Volume: Blood level should be to line on label (may be over)
Analyte Stability:
| Specimen Type | Temperature | Time |
|---|---|---|
| Whole Blood (unprocessed) | Ambient | 4 hours |
| Plasma (processed) | Refrigerated (preferred) | 4 hours |
| Ambient | 4 hours | |
| Frozen (-20c) | 1 month |
Test Classification and CPT Code
85730
LOINC
14979-9
Last Reviewed
07/2025