A dialysis catheter is a specific type of Central Venous Catheter (CVC) inserted into a large vein, typically in the neck or chest, designed to provide access for hemodialysis treatment. Its primary function is to allow high volumes of blood to be rapidly removed, cleaned by the dialysis machine, and returned to the body. While it is technically possible to draw blood samples from a dialysis catheter, this practice is generally discouraged for routine laboratory work. Blood draws from this device are reserved for specific circumstances and must only be performed by highly trained personnel following a stringent protocol.
Primary Function and Catheter Design
The physical design of a dialysis catheter is unique, featuring two large-bore lumens—an arterial line and a venous line—to support the high flow rates necessary for effective blood purification. These high flow rates, often exceeding 300 milliliters per minute, are achievable because the catheter resides within a large central vein.
To maintain the catheter’s patency between dialysis sessions, the lumens are filled with a specialized anticoagulant solution, known as a catheter lock. Common lock solutions include various concentrations of heparin (e.g., 1,000 units per milliliter) or a sodium citrate solution (often 4%).
These solutions prevent blood from clotting inside the catheter, which is essential for its long-term function. Because the lock solution occupies the internal volume, any blood sample drawn must first clear this substance to avoid diluting the sample and skewing laboratory results. This double-lumen design and the presence of the lock solution necessitate a specific, careful procedure for blood collection.
The Standard Protocol for Blood Draws
When a blood draw from a dialysis catheter is authorized, a meticulous, multi-step protocol must be strictly followed to protect the patient and the integrity of the sample. The procedure begins with the application of a strict aseptic, or sterile, technique to prevent the introduction of bacteria into the line and bloodstream. The catheter hub is thoroughly disinfected before any connection is made.
A syringe is attached to the arterial lumen, which is the preferred port for blood collection. An initial volume of blood is withdrawn and discarded, a step often referred to as the “waste.” This waste volume is necessary to completely clear the lumen of the anticoagulant lock solution and any contaminated blood.
The volume discarded typically ranges from 3 to 10 milliliters, or at least two times the internal volume of the catheter, depending on the specific device and facility protocol. Following the waste collection, the laboratory samples are drawn using new, sterile syringes or a specialized adapter.
Once the required samples are collected, the catheter lumen is flushed with a sterile saline solution to ensure no blood remains, which could lead to clotting. Finally, the original anticoagulant lock solution is carefully re-instilled into the lumen to the exact specified volume, sealing it until the next dialysis treatment.
Major Risks and Compromising Catheter Integrity
Using a dialysis catheter for routine blood draws significantly increases the risk of complications, which is why it is not the preferred method. The most serious risk is the development of a Central Line Associated Bloodstream Infection (CLABSI). Frequent manipulation of the catheter hubs for non-dialysis purposes provides additional opportunities for bacteria to enter the bloodstream, potentially leading to sepsis.
Dialysis catheters are already associated with a higher rate of infection compared to other vascular access types, such as fistulas or grafts. Approximately 70% of all dialysis-related bloodstream infections occur in patients who rely on a catheter for their treatment. Each time the catheter is accessed for a blood draw, the risk of contamination increases, potentially leading to a systemic infection.
Additional risks include damage to the catheter and the formation of blood clots within the lumen. The repeated opening and closing of the line, along with the necessary flushing and relocking procedures, can lead to mechanical stress or inadequate maintenance of the anticoagulant lock. Catheter dysfunction due to clotting compromises the ability to perform efficient dialysis. Preserving the catheter’s function and minimizing the risk of infection are paramount to the patient’s overall health.
Recommended Standard Blood Collection Methods
To protect the dialysis catheter and minimize associated risks, routine blood work is preferentially collected using alternative methods. The safest and most common technique is standard peripheral venipuncture, which involves drawing blood from a vein in the arm, wrist, or hand. This method avoids the manipulation of the central catheter entirely, eliminating the risk of a CLABSI associated with the access device.
In some controlled settings, blood samples can be collected from the needles inserted into a patient’s arteriovenous fistula or graft. This collection must happen immediately after the dialysis needles are placed and before the patient is connected to the dialysis circuit. This strategy is employed to prevent unnecessary needle sticks for the patient, but standard venipuncture remains the preferred and lowest-risk option for routine lab testing.