Relationship between peak anti-Xa levels and calculated creatinine clearance in ICU patients receiving low molecular weight heparin

Objective

To evaluate serial anti-Xa 'peak' levels drawn 2 or 4 hours post LMWH prophylaxis in 13 consecutive ICU patients with a range of renal function.

Setting

Multidisciplinary, closed, university-affiliated 15-bed medical–surgical ICU.

Method

We measured anti-Xa blood levels either 2 or 4 hours post dalteparin administration each day until death or discharge. We calculated creatinine clearance daily using the Cockroft-Gault formula. We graphed these peak anti-Xa levels against calculated creatinine clearance values, and examined their relation to bleeding events.

Results

We performed 287 anti-Xa levels on these ICU patients, and found that peak anti-Xa levels were consistently less than 0.5 U/ml. We did not demonstrate a relationship between the timing of the peak anti-Xa levels, and a) the value of the peak anti-Xa levels, b) the patients' calculated creatinine clearance, or c) bleeding events.

Conclusions

Anti-Xa levels drawn 2 or 4 hours post subcutaneous injection of 5000 U dalteparin in this sample of patients were consistently less than 0.5 U/ml, but did not vary significantly with renal function.