Anti-factor Xa level monitoring in patients receiving prophylactic enoxaparin is increasingly common.

We report on a series of cancer patients with therapeutic or supratherapeutic anti-Factor Xa levels while on prophylactic doses of enoxaparin after surgical procedures.

Elevated anti-Factor Xa levels can result from heparin contamination of anti-Factor Xa specimens removed from central lines or chemoports.

Inappropriately drawn anti-Factor Xa levels may contribute to prophylaxis interruption or unnecessary workup for renal or liver failure.