What are the recommended methods for sending a blood sample from a patient undergoing dialysis to minimize infection and contamination risk?

Blood Sampling Methods During Dialysis

For blood sampling during hemodialysis, use the arterial needle or port before connecting the bloodlines and initiating dialysis, ensuring proper technique to avoid contamination with flush solutions or heparin that could compromise sample accuracy and patient safety. 1

Pre-Dialysis Blood Sampling Technique

For Arteriovenous Fistula or Graft Access

• Obtain the blood specimen directly from the arterial needle prior to connecting the arterial blood tubing or flushing the needle to prevent dilution of the blood sample with saline or heparin 1
• Ensure no saline or heparin is present in the arterial needle and tubing before drawing the sample 1
• Never draw a sample if hemodialysis has already been initiated, as this will reflect dialyzed blood and produce inaccurate results 1

For Venous Catheter Access

• Withdraw any heparin and saline from the arterial port of the catheter first, following your dialysis unit's protocol to prevent sample dilution 1
• For adult patients, withdraw and discard (or save for reinfusion) 10 mL of blood from the arterial port using sterile technique before collecting the actual sample 1
• For pediatric patients, withdraw 3-5 mL according to the catheter's fill volume, as smaller patients and catheters require reduced volumes 1
• Connect a new syringe or collection device and draw the sample for laboratory measurement only after the dead space has been cleared 1

Post-Dialysis Blood Sampling Considerations

Timing is critical for post-dialysis samples due to urea rebound and access recirculation effects. 1

• Avoid immediate post-dialysis sampling, as blood remaining in the vascular access may be recirculated blood that has not passed through urea-rich tissues 1
• The late phase of urea rebound completes within 30-60 minutes after cessation of dialysis 1

Infection Prevention During Blood Sampling

Standard Precautions for All Samples

• Use proper skin preparation with alcoholic chlorhexidine (>0.5%), alcohol, or tincture of iodine rather than povidone-iodine when obtaining blood cultures 2
• Maintain strict aseptic technique throughout the sampling process to minimize contamination risk 1
• Perform hand hygiene before and after blood sampling procedures 1

Blood Culture Collection Specifics

• Draw blood cultures before initiating antibiotics to maximize diagnostic yield 2
• Obtain blood cultures from both a peripheral vein and through the catheter if peripheral access is unavailable 2
• For patients with suspected catheter-related bloodstream infection, swab any drainage for Gram stain and culture to identify the causative organism 2

Critical Pitfalls to Avoid

Sample Contamination Errors

Contamination with glucose-containing flush solutions can produce dangerously misleading results. 1

• Even with 5× dead space removal, significant glucose contamination occurs when using glucose 5% flush solution in open arterial line systems 1
• A glucose 5% solution contains approximately 280 mmol/L; contamination of just 0.03 mL in a 1-mL blood sample can conceal true hypoglycemia or create false hyperglycemia 1
• Contamination with heparinized saline also leads to artifactually increased phosphate concentrations 1
• Erratic or highly varying sequential test results should heighten suspicion of blood sample contamination error 1

Closed vs. Open Sampling Systems

• Closed systems with a port for dead space removal beyond a separate sampling point effectively eliminate the risk of significant sample contamination 1
• Closed systems also reduce bacteremia risk and minimize blood wastage because withdrawn flush and blood can be returned to circulation without opening the system 1
• Open systems with a single three-way tap used for both removing residual flush and obtaining samples carry higher contamination risk 1

Special Considerations for Dialysis Patients

Peripheral Vein Preservation

• Avoid drawing blood from peripheral veins that will be used for future creation of a fistula or graft, as venipuncture may injure the vein 1
• Many dialysis patients have exhausted peripheral veins due to multiple failed dialysis fistulas or grafts, making it frequently not feasible to obtain peripheral blood samples 1

Laboratory Processing Accuracy

• Ensure laboratory processing of samples is accurate, as this is essential for proper measurement of delivered dialysis dose and other parameters 1
• Predialysis samples must be obtained without dilution to prevent falsely low measurements 1