Treatment: LMWH (low-molecular-weight heparin)

Cardiovascular · Treatment monitoring · updated 2026-11-08

BioMG follows French guidelines. Adapt it to the guidelines and the tests available where you practise.

Frequency: In France, 1.7 million people covered by the general health insurance scheme received an LMWH at least once in 2011 (number of patients with at least one reimbursement; old data, no update found) ^[1].

Intermediate risk of HIT: LMWH after surgery, major trauma, or in a patient with cancer

Laboratory tests

Platelet count
Do before the first injection (at the latest before day 4), then 1 to twice a week from day 4 to day 14, then once a week up to 1 month if treatment continues.

Detailed explanation and international comparison (in French): read it in English (machine translation)

Do not order

Routine anti-Xa activity: routine monitoring of anti-Xa activity is recommended neither for LMWH nor for fondaparinux ^[2].

Low risk of HIT: LMWH for medical patients without cancer (including phlebitis), pregnancy without surgery, minor trauma, or treatment for more than one month

Laboratory tests

Platelet count
Do before starting treatment
and repeat if HIT (heparin-induced thrombocytopenia) is clinically suspected

Detailed explanation and international comparison (in French): read it in English (machine translation)

Do not order

Routine and repeated platelet count on LMWH, in a non-surgical and non-trauma setting in a patient not at risk: not routine, only in the presence of clinical features suggesting HIT ^[2,3].

Renal function and serum potassium (renal impairment, diabetes, drugs raising potassium)

Laboratory tests

Serum creatinine with eGFR
Serum electrolytes (potassium)if neededPatient at risk of hyperkalaemia on heparin: diabetes, chronic renal failure, metabolic acidosis, potassium-raising drugs; the SmPC (RCP) asks for regular potassium monitoring ^[6]. The tinzaparin, dalteparin and nadroparin SmPCs (RCP) give the same warning ^[5,7,8].
Anti-Xa activityif neededRenal failure (increased exposure and higher bleeding risk): the SmPC (RCP) states that measuring anti-Xa activity “could be considered” ^[6]; the 2019 recommendation notes that it has no validated evidence ^[2]. The dalteparin (clearance 30 to 60 mL/min) and tinzaparin (clearance 20 to 30 mL/min) SmPCs (RCP) ask to adjust the dose on anti-Xa activity ^[7,8]; SPLF recommends not measuring it on LMWH (grade 1−) ^[14].

Detailed explanation and international comparison (in French): read it in English (machine translation)

Do not order

Routine anti-Xa activity, including in moderate renal failure or in patients at high bleeding risk (age, low weight): laboratory monitoring might help control the risk, “without clear validated evidence” ^[2].

Sources (17)