What is a citrate lock?

Citrate Lock for Central Venous Catheters

A citrate lock is an antimicrobial and antithrombotic solution instilled into the lumen of a central venous catheter (CVC) during the interdialytic period to maintain catheter patency and prevent catheter-related bloodstream infections (CRBSI). 1

Mechanism of Action

• Citrate functions as both an anticoagulant and antimicrobial agent by chelating calcium, which disrupts the normal coagulation pathway and interferes with bacterial biofilm formation 2
• Unlike heparin, which may enhance biofilm growth, citrate actively prevents biofilm formation and has inherent antimicrobial properties 1
• Citrate's dual action helps maintain catheter patency while reducing infection risk, addressing the two major complications of central venous catheters 1

Formulations and Concentrations

• Low-concentration citrate (<5%) is the preferred formulation for CVC locks as recommended by KDOQI guidelines 1
• Citrate 4% is the most commonly available concentration in the United States, as higher concentrations (46.7%) were removed from the market in 2000 due to safety concerns 2
• FDA-approved citrate solution contains 4g sodium citrate dihydrate per 100mL, with pH adjusted using citric acid 3
• Antimicrobial-containing citrate locks combine citrate with agents like gentamicin, taurolidine, methylene blue, or methylparaben for enhanced infection prevention 4

Efficacy

Infection Prevention

• Antimicrobial-containing citrate locks significantly reduce catheter-related bloodstream infections compared to heparin locks (risk ratio 0.39; 95% CI, 0.27-0.56) 4
• A prospective multicenter study showed gentamicin-citrate solution reduced CRBSI by 73% compared to heparin (0.45 vs 1.68 per 1,000 catheter-days) 1
• Citrate alone (without antimicrobial additives) has not consistently demonstrated superior infection prevention compared to heparin 4

Catheter Patency

• Low-concentration citrate (4-5%) is equally effective as heparin in maintaining catheter patency 5, 6
• A randomized controlled trial comparing 5% vs 10% citrate found no significant difference in preventing large clot formation or complete catheter obstruction 5
• Using citrate locks may reduce the risk of systemic anticoagulation and bleeding compared to heparin 2

Clinical Applications

• KDOQI guidelines suggest using low-concentration citrate (<5%) CVC locking solution to help prevent CRBSI and CVC dysfunction 1
• Citrate locks are particularly beneficial for patients with high bleeding risk, as they reduce bleeding episodes compared to heparin (RR, 0.48; 95% CI, 0.30-0.76) 4
• For hemodialysis catheters with recurrent dysfunction, KDOQI recommends using alteplase or urokinase plus citrate 4% per limb for restoring intraluminal blood flow 1
• Citrate locks are especially valuable for patients with a history of multiple CRBSIs or those with long-term catheter placement 1

Safety Considerations

• Low-concentration citrate (4%) has not been associated with the systemic hypocalcemic effects reported with high-concentration citrate (46.7%) 2
• The injected volume should not exceed the internal volume of the catheter to prevent systemic effects 6
• Currently, there are no FDA-approved commercial lock formulations; solutions are typically prepared locally in hospital pharmacies 1
• The FDA has approved citrate 4% solution specifically for use with automated apheresis devices, though it is commonly used off-label as a catheter lock 3

Practical Implementation

• The choice between citrate or heparin as a CVC locking solution should be based on patient-specific factors such as bleeding risk and infection history 1
• For patients with recurrent catheter-related infections, antimicrobial-containing citrate locks provide superior protection 4
• For patients with bleeding disorders or heparin-induced thrombocytopenia, citrate locks offer a safer alternative to heparin 2
• Regular monitoring of catheter function and inspection for signs of infection should be performed regardless of the locking solution used 1