Venous thromboembolism prophylaxis: heparin-induced thrombocytopenia was reduced by using LMWH.

Clinical bottom line (level 1b)

  1. About 3% of patients on heparin for venous thromboembolism prophylaxis developed heparin-induced thrombocytopenia.
  2. Patients with heparin-induced thrombocytopenia were at a greatly increased risk for venous thromboembolism compared with patients with normal levels of platelets on heparin or LMWH (NNF = 1 for unknown) .
  3. Patients on LMWH had less heparin-induced thrombocytopenia (NNT = 37 at 5 days) .
Warkentin et al: New England Journal of Medicine 1995; 332 (20): 1330-1335
Expires June 2003

The study

Double-blinded concealed randomised trial with intention-to-treat
Setting: tertiary centre, Canada

665 patients (aged ?, ?% male) undergoing hip surgery
Note:
  • Patients had platelet counts measured pre-operatively and daily for 14 days or until discharge.


    • Control Group: (n = 332, 332 analysed): unfractionated heparin 7500 units twice daily subcutaneously post-operative prophylaxis
    Experimental Group: (n = 333, 333 analysed): enoxaparin 30 mg twice daily subcutaneously post-operative prophylaxis

    100% followed for 14 days
    Outcome notes:
    • heparin-induced thrombocytopenia : platelet <150 for two days after five days of treatment with prophylaxis and heparin-dependent IgG antibodies detected
    • early post-operative thrombocytopenia : defined if occurred post-op day 1-3 (a common consequence of surgery)

    The evidence

    Outcome Time to outcome CEREERRRR
    (95% CI)    		ARR
    (95% CI)    		NNT
    (95% CI)
    heparin-induced thrombocytopenia 5 days 9
    (2.71%)    		 0
    (0.00%)    		 100%
    (% to %)    		 2.71%
    (0.96% to 4.46%)    		 37
    (22 to 100)
    early post-operative thrombocytopenia 3 days 93
    (28.0%)    		 96
    (28.8%)    		 -3%
    (-31% to 19%)    		 -0.82%
    (-7.67% to 6.04%)    		 -120
    (NNT = 17 to infinity;
    NNH = 13 to infinity)

    Outcome Time to outcome CER OR
    (95% CI)    		 NNF
    (95% CI)
    venous thromboembolism unknown /
    (%)    		 4.98
    (3.75 to 6.62)     		1
    (1 to 2)

  • LMWH produced no thrombocytopenia in this study: 95% CI: 0% to 0.90%.

    • Comments

    1. Note relative risk was not adjusted for confounding factors- eg. many of the patients without thrombocytopenia were on LMWH, which is better at reducing VTE than unfractionated heparin.

    Citation

    1. Warkentin TE, Levine MN, Hirsh J, et al: Heparin-induced thrombocytopenia in patients treated with low-molecular-weight heparin or unfractionated heparin. New England Journal of Medicine 1995; 332 (20): 1330-1335
    Search Terms: thrombocytopen* and heparin in Cochrane
    Contributor: Chris Ball and Clare Wotton, June 2000
    Reviewer:

    Clinical Question.
    Patient hip surgery
    Intervention or Exposure enoxaparin
    Comparison unfractionated heparin
    Outcome thrombocytopenia