Prothrombin Time : 1000758

Send ambient whole blood only if the specimen can arrive in the laboratory within 24 hours of collection. If greater than 24 hours, send frozen plasma. Frozen aliquot must remain frozen. Freeze thaw cycle will adversely affect specimen integrity.

Test Code
PT or 1000758

Alias/See Also
INR; Prothrombin Time, Plasma; Protime; PT

CPT Codes

Blue top tube, 3.2% sodium citrate. • Obtain venous blood by clean venipuncture. Avoid slow-flowing draws and/or traumatic venipunctures as either of these may result in an activated or clotted specimen. Do not use needles smaller than 23 gauge. Do not leave the tourniquet on for an extended length of time before drawing the sample. • A pilot tube (non-additive or light blue tube) before drawing coagulation specimens in light blue vacuum tubes is only necessary when using a butterfly blood collection set as this will cause reduced draw volume in the first tube. Discard the pilot tube. • Fill light blue tubes as far as vacuum will allow and mix by gentle inversion. Exact ratio of nine parts blood to one part anticoagulant must be maintained. Inadequate filling of the sample tube will alter this ratio and may lead to inaccurate results. Patients who have hematocrit values above 55 percent should have the anticoagulant adjusted to maintain the 9:1 ratio. Use the following formula to determine the amount of anticoagulant to use: [(100 – Hct) / (595 – Hct) ]* total volume = amount of anticoagulant required. • After collecting the blood, examine the tube to ensure that it is filled to within 90% of the fill line. • Note: Specimens containing heparin should not be used for coagulation studies. If possible, stop heparin therapy before the draw to avoid contamination. Heparin interferes with most clotting assays. If heparinized line must be used to obtain the sample, flush line with 5mL saline and discard the first 5 mL of blood drawn into a syringe, or 6 “dead space” volumes of the line.

Transport Container
Blue top whole blood (Min. 3 mL): deliver to lab at room temperature within 24 hours. If the specimen cannot arrive in the laboratory within 24 hours of collection, the specimen must be centrifuged, aliquoted, and frozen. Processing instructions: Centrifuge at a rate and speed to yield platelet poor plasma (<10,000/uL), immediately remove only the top two-thirds of the platelet-poor plasma from the specimen using a plastic-transfer pipet (use of glass-transfer pipets may result in activation and/or clotting of the plasma) and transfer citrated plasma (Min. 0.5 mL) into a standard transport tube, and freeze the aliquot.

Transport Temperature
Citrated whole blood: Ambient
Citrated plasma: Frozen

Specimen Stability
Whole blood:  Ambient: 24 hours
Plasma after separation from cells: Ambient: Unacceptable; Refrigerated: Unacceptable; Frozen: 14 days

Reject Criteria (Eg, hemolysis? Lipemia? Thaw/Other?)
Tubes not filled within 90% of the fill line will be rejected by the lab.


Setup Schedule
Sunday - Saturday

Report Available
1 day

Reference Range
0 to <4 days:                                      10.2-15.4 seconds
>=4 days to <7 months:                      9.9-13.6 seconds
>= 7 months to <18 years:                    9.7-12.3 seconds
>= 18 years:                                         9.0-12.0 seconds

Coumarin Anticoagulant Therapeutic Ranges (INR):
2.0-3.0  Prophylaxis and Treatment of Venous Thromboembolism
2.5-3.5  Prevention of Recurrent Thromboembolism or treatment for Prosthetic Heart Valves

Clinical Significance
The Prothrombin Time Test (PT) is a global clotting-based assay to evaluate the extrinsic and common coagulation pathways. The PT has three major applications. These include:

1. Detection of single or combined deficiencies of the extrinsic coagulation pathway indicative of hereditary and acquired coagulation disorders, liver disease, or Vitamin K deficiency;

2. A sensitive monitoring test for oral anticoagulant therapy when combined with INR reporting;

3. An assay for specific coagulation factors. The PT is sensitive to the levels of Factors II, V, VII, and X.

The coagulation cascade is activated by incubating plasma with the optimal amount of thromboplastin and calcium at 37°C. The PT is the time in seconds required for a fibrin clot to form.

The International Normalized Ratio (INR) provides a convenient method for monitoring warfarin therapy. Reported INR results are less dependent on reagents and methods used. The INR provides the clinician with an improved means for minimizing variability between different laboratories, PT reagents, and test methodologies, thus potentially improving the consistency of long-term therapeutic monitoring.


Plasma collection and storage conditions must be carefully controlled. Avoid small plasma volumes prior to testing which may cause pH changes in the plasma leading to inactivation of specific components of the coagulation system. Oral anticoagulants such as warfarin depress the production of Factors II, VII, IX, and X in the liver by inhibiting the action of Vitamin K. Many commonly administered drugs may affect the PT results. These should be considered when unusual or unexpected abnormal results are obtained. Unexpected abnormal results should be followed by further coagulation studies to determine the source of the abnormality. Nonspecific inhibitors such as Lupus anticoagulant or specific factor inhibitors may interfere with the PT and possibly result in INRs that do not reflect the exact degree of anticoagulation. Direct thrombin inhibitors in therapeutic doses result in prolonged prothrombin times.

Performing Laboratory
med fusion

The CPT Codes provided in this document are based on AMA guidelines and are for informational purposes only. CPT coding is the sole responsibility of the billing party. Please direct any questions regarding coding to the payor being billed. Any Profile/panel component may be ordered separately. Reflex tests are performed at an additional charge.