should aptts be used to predict heparin levels?

1
18 THERAPY PHARMACOLOGY Should APITs be used to predict heparin levels? Heparin levels cannot be accurately predicted using the activated partial thromboplastin time (APTT), report researchers from the VS. In the first part of this study, 38 patients receiving IV heparin underwent simultaneous measurement of APTT and anti factor Xa levels. Wide prediction interval A therapeutic APTT range was established at 59-84 seconds (calibration was perfonned according to current recommendations). Regression analysis demonstrated the R2 value to be 0.4. For an APTT of 60 seconds, the predicted heparin level was 0.53 Vlml with a 95% prediction interval of 0.05-1.0 Vlml.* Thus, the researchers note that the precision of the calibration method was poor, as the prediction interval extended above and below the therapeutic range for heparin. In the second part of the study, 27 patients receiving IV heparin each had 5 AP'IT and anti- factor Xa assays perfonned. Three paired sets of APTT and antifactor Xa assays were then used to establish an individualised therapeutic range in each patient. 'No reliable relationship' The researchers comment that analysis of data demonstrated that although in many patients the correlation between the APTT and the antifactor Xa levels is 'fairly good', in other patients 'there is no reliable relationship' (average R2 of 0.75). In addition, among the patients with a high cor- relation between APTT and antifactor Xa levels, the confidence intervals are too broad to be clinically useful. The researchers conclude that when the APTT is outside the therapeutic range, decisions for adjusting heparin dosing based on the APTT will be wrong most of the time. They suggest that recommendations on the use of heparin levels should be expanded to include all patients. According to recently published guidelines, monitoring of heparin levels is only recommended in patients whose APTT response is less than the lower limit of the therapeutic range, despite receiving heparin doses of 40 000 V/day, note the researchers. * The prediction inJerval estimates the antifactor XJJ value for a particular patienl from a givenAPJTvaJue. Baker BA, Adelman MD, Smith PA, Osborn le. Inability of the activated partial thromboplastin time to predict heparin levels: time to reassess guidelines for heparin assays. Archives ofIntemal Medicine 157: 2475-2479,24 Nov 1997 Il00616407 Inpharma-20 Dec 11187 No. 111. 1173-8324197/1118-000181$01.000 AdlalnternlitloNlI Limited 11187. All rights nneMICI

Post on 11-Dec-2016

212 views

Category:

Documents


0 download

TRANSCRIPT

Page 1: Should APTTs be used to predict heparin levels?

18 THERAPY

PHARMACOLOGY Should APITs be used to predict heparin levels?

Heparin levels cannot be accurately predicted using the activated partial thromboplastin time (APTT), report researchers from the VS.

In the first part of this study, 38 patients receiving IV heparin underwent simultaneous measurement of APTT and anti factor Xa levels.

Wide prediction interval A therapeutic APTT range was established at

59-84 seconds (calibration was perfonned according to current recommendations). Regression analysis demonstrated the R2 value to be 0.4. For an APTT of 60 seconds, the predicted heparin level was 0.53 Vlml with a 95% prediction interval of 0.05-1.0 Vlml.* Thus, the researchers note that the precision of the calibration method was poor, as the prediction interval extended above and below the therapeutic range for heparin.

In the second part of the study, 27 patients receiving IV heparin each had ~ 5 AP'IT and anti­factor Xa assays perfonned.

Three paired sets of APTT and antifactor Xa assays were then used to establish an individualised therapeutic range in each patient.

'No reliable relationship' The researchers comment that analysis of data

demonstrated that although in many patients the correlation between the APTT and the antifactor Xa levels is 'fairly good', in other patients 'there is no reliable relationship' (average R2 of 0.75). In addition, among the patients with a high cor­relation between APTT and antifactor Xa levels, the confidence intervals are too broad to be clinically useful.

The researchers conclude that when the APTT is outside the therapeutic range, decisions for adjusting heparin dosing based on the APTT will be wrong most of the time. They suggest that recommendations on

the use of heparin levels should be expanded to include all patients.

According to recently published guidelines, monitoring of heparin levels is only recommended in patients whose APTT response is less than the lower limit of the therapeutic range, despite receiving heparin doses of 40 000 V/day, note the researchers.

* The prediction inJerval estimates the antifactor XJJ value for a particular patienl from a givenAPJTvaJue.

Baker BA, Adelman MD, Smith PA, Osborn le. Inability of the activated partial thromboplastin time to predict heparin levels: time to reassess guidelines for heparin assays. Archives ofIntemal Medicine 157: 2475-2479,24 Nov 1997

Il00616407

Inpharma-20 Dec 11187 No. 111. 1173-8324197/1118-000181$01.000 AdlalnternlitloNlI Limited 11187. All rights nneMICI