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Reference Interval for Pediatric PTs

From Colleen Marinucci at Elmendorf AFB in Alaska:

Our pediatrician uses “The Harriet Lane Handbook: A Manual for Pediatric House Officers” for coagulation reference ranges and said 10.6-11.4 seconds is an age specific range for the prothrombin time. Our adult range is 10.7-14.3. Her four-yo patient resulted twice at 14.6 seconds and has a history of epistaxis. She felt this abnormal result warrented a mixing study.
Any comments?

Hi, Colleen. Thank you for your question. The Harriet Lane Handbook, which you will find in the lab coat pocket of every pediatric resident, and most clinical texts reference Andrew M, Vegh P, Johnston M. et al: Maturation of the Hemostatic System During Childhood. Blood 1992; 80: 1998-2005, seminal research directed by the late Maureen Andrew, and available from the American Society of Hematology as a free download. According to Andrew, 10.6 to 11.4 seconds is the correct reference interval for a four year old, so your pediatrician is correct to pursue follow-up studies. I hope this is helpful. Geo

Comments (5)
May 16, 2011 7:17am

Hello (perhaps better buenas dias). I live in France and wor
Hello (perhaps better buenas dias). I live in France and work for Stago. Whatever in France it is still percentage that is used and not seconds for PT results. And I totally acknowledge with you that physicians are in trouble with INR. As INR is determined by the ISI himself determined by a comparison between only normal and VKA patients tested by the reference thromboplastin and each lot of the thromboplastin manufactured it won’t be used for other patient ( e.g. hepatic dysfunction).

From Geo: Thanks to Dr. Morer for this confirmation, it appears that many of us are using the prothrombin time ratio in percentage.

May 15, 2011 7:56pm

Thanks. I live in Argentina. Here there is a external qc tha
Thanks. I live in Argentina. Here there is a external qc that compares the values in % of APP, not in seconds because the dispersion would be big I think. Due to the difference between Argentinian and home made reagents, % is a excellent way to compare PT of different manufacturers. In summary for me is still useful. INR only applies in anticoagulated patients and % in the others. Physician confuse it utility. VR: 70-120 % PAP

May 13, 2011 6:02am

You may read too Monagle P, et al. Thromb Haemost 2006; 95:3
You may read too Monagle P, et al. Thromb Haemost 2006; 95:362-372. Normal value for children 1-5 years:
STA NeoCI plus 13.3 (12.1-14.5) and STA NéoR 13.9 ( 13.0-14.8)

Also Summerhayes R, et al, J Thromb Haemost 2009, 7 Supp 2 : P-WE-480; Summerhayes R. et al, J Thromb Haemost 2007, 5 Supp 2: P-M-105; and Summerhayes R. et al J Thromb Haemost 2007, 5 Supp 2: P-S-397.
Best regards.

May 12, 2011 9:12pm

%APP = (TPc-b/TPp-b)*100
I Apply this f

%APP = (TPc-b/TPp-b)*100
I Apply this formula with MS Excel and it is in agreement with the coagulometers curve, only a minimal difference.
when the lot of reagent changes, I put the new pool pt values at 100% and 50% to obtain a new chart. Creation of formula is time-requiring, but everlasting useful!

May 12, 2011 9:04pm

Hello. In my opinion the reference value for PT is not in se
Hello. In my opinion the reference value for PT is not in seconds, rather in % prothrombin time activity of plasma.The books I read didn’t define value in seconds but physicians use to believe that is correct. And biochemist colleagues that don’t practice coagulation test actually don’t know well. Because of that is necessary to educate professionals for incorporate these concepts. Is wrong that PT RV express in seconds!

From George: Thank you for your comment. Percent prothrombin time (PT), defined as the ratio of patient PT Vs. the mean of the PT reference interval expressed as a percentage, though a useful enough reporting form, has fallen into disuse since the international normalized ratio (INR) was developed. Most physicians refer to the INR for monitoring warfarin therapy but employ the PT in seconds when using the assay as a coagulopathy screen. In this case, the physician compares the patient’s result in seconds to the reference interval, published in seconds.

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