Prothrombin Time (PT) and Partial Thromboplastin Time (PTT)

CPT: 85610; 85730
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  • Activated Partial Thromboplastin Time (aPTT) and Prothrombin Time (PT)
  • PT and aPTT
  • PT and PTT

Test Includes

Activated partial thromboplastin time (aPTT); international normalized ratio (INR); prothrombin time (PT)

Special Instructions

This aPTT test is for screening purposes only and is not intended for therapeutic monitoring. Please refer to Heparin Anti-Xa [117101] and thrombin inhibitors, etc for aPTT testing. If the patient's hematocrit exceeds 55%, the volume of citrate in the collection tube must be adjusted. Refer Coagulation Collection Procedures for directions.

Expected Turnaround Time

Within 1 day

Related Documents

For more information, please view the literature below.

Procedures for Hemostasis and Thrombosis: A Clinical Test Compendium

Specimen Requirements


Whole blood, plasma


4.5 mL, 2.7 mL, 1.8 mL

Minimum Volume

90% of full draw


Blue-top (sodium citrate) tube; do not open tube unless plasma is to be frozen.


Blood should be collected in a blue-top tube containing 3.2% buffered sodium citrate.1 Evacuated collection tubes must be filled to completion to ensure a proper blood to anticoagulant ratio.2,3 The sample should be mixed immediately by gentle inversion at least six times to ensure adequate mixing of the anticoagulant with the blood. A discard tube is not required prior to collection of coagulation samples.4,5 When noncitrate tubes are collected for other tests, collect sterile and nonadditive (red-top) tubes prior to citrate (blue-top) tubes. Any tube containing an alternate anticoagulant should be collected after the blue-top tube. Gel-barrier tubes and serum tubes with clot initiators should also be collected after the citrate tubes. To avoid delays in turnaround time when requesting multiple tests on frozen samples, please submit separate frozen specimens for each test requested.

Please print and use the Volume Guide for Coagulation Testing to ensure proper draw volume.

Storage Instructions

Specimens are stable at room temperature for 24 hours. If testing cannot be completed within 24 hours, specimens should be centrifuged for at least 10 minutes at 1500xg. Plasma should then be transferred to a Labcorp PP transpak frozen purple tube with screw cap (Labcorp No. 49482). Freeze immediately and maintain frozen until tested. Refer to Coagulation Collection Procedures for directions.

Requirements for patients receiving heparin are different: If testing cannot be performed within one hour of collection, frozen plasma must be submitted. Specimens should be centrifuged for at least 15 minutes at 1500xg to produce platelet-poor plasma, and the plasma quick frozen and maintained in this condition until tested.

Patient Preparation

Draw specimen one hour before next dose of heparin if heparin is being given by intermittent injection. Do not draw from an arm with a heparin lock or heparinized catheter.

Causes for Rejection

Gross hemolysis; clotted specimen; frozen specimen thawed in transit; tubes <90% full; improper labeling; specimen collected in tube other than 3.2% citrate; refrigerated sample

Test Details

Reference Interval

See table.



Activated Partial Thromboplastin Time (aPTT)

0 to 3 d

Not established

4 d to 6 m

26−38 sec

7 m to 17 y

26−35 sec

≥18 y

24−33 sec

Prothrombin Time (PT)

0 to 30 d

9.8−13.2 sec

1 to 6 m

9.8−12.6 sec

7 m to 1 y

9.8−12.2 sec

2 to 17 y

9.9–12.1 sec

≥18 y

9.1−12.0 sec

International Normalized Ratio (INR)

0 to 1 m


>1 m


Additional Information

See descriptions of individual tests.


1. Adcock DM, Kressin DC, Marlar RA. Effect of 3.2% vs 3.8% sodium citrate concentration on routine coagulation testing. Am J Clin Pathol. 1997Jan; 107(1):105-110. 8980376
2. Reneke J, Etzell J, Leslie S, Ng VL, Gottfried EL. Prolonged prothrombin time and activated partial thromboplastin time due to underfilled specimen tubes with 109 mmol/L (3.2%) citrate anticoagulant. Am J Clin Pathol. 1998 Jun; 109(6):754-757.9620035
3. National Committee for Clinical Laboratory Standardization. Collection, Transport, and Processing of Blood Specimens for Coagulation Testing and General Performance of Coagulation Assays; Approved Guideline. 5th ed. Villanova, Pa: NCCLS; 2008. Document H21-A5:28(5).
4. Gottfried EL, Adachi MM. Prothrombin time and activated partial thromboplastin time can be performed on the first tube. Am J Clin Pathol. 1997 Jun; 107(6):681-683. 9169665
5. McGlasson DL, More L, Best HA, Norris WL, Doe RH, Ray H. Drawing specimens for coagulation testing: Is a second tube necessary? Clin Lab Sci. 1999 May-Jun; 12(3):137-139. 10539100


Order Code Order Code Name Order Loinc Result Code Result Code Name UofM Result LOINC
020321 PT and PTT 34529-8 115107 INR 6301-6
020321 PT and PTT 34529-8 015289 Prothrombin Time sec 5902-2
020321 PT and PTT 34529-8 015116 aPTT sec 14979-9
Reflex Table for INR
Order Code Order Name Result Code Result Name UofM Result LOINC
Reflex 1 115109 INR (Thromborel-S) 115109 INR (Thromborel-S) 6301-6
Reflex Table for Prothrombin Time
Order Code Order Name Result Code Result Name UofM Result LOINC
Reflex 1 015290 PT (Thromborel-S) 015290 PT (Thromborel-S) sec 5902-2

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