Interferences

There are a variety of different factors that can interfere with laboratory results. The following provides an overview of possible interferences.

Specimen Integrity Issues

Hemolysis

Hemolysis can interfere directly with lab results (due to the release of red blood cell components) or indirectly by affecting

• May be due to patient's condition (e.g., hemolytic anemia, autoimmune conditions, certain drugs, etc.)
• May be due to improper specimen collection (e.g., too much force during venipuncture due to small needle gauge or pulling too hard on syringe, slow draws, excess damage to tissue during venipuncture, excessive mixing, etc.)

Tests most affected by hemolysis include:

• Potassium
• ALP
• LDH
• RBC
• Hemoglobin
• Hematocrit

Lipemia

• Cloudiness of sample due to lipemia affects photometric methods
• May be caused by recent fatty meals or be due to a patient's condition
• Lipemia can be removed by ultracentrifugation of samples
  • Do not ultracentrifuge lipid, cholesterol, triglyceride, etc. tests as this removes the fats

Other Factors

• Quantity not sufficient
  • Insufficient sample volumes may cause aspiration errors and cause false results
• Clotted specimen
  • Serum samples may require 30 minutes or more to fully clot before being centrifuged; the use of clot activators (silica, thrombin, etc.) can reduce the clotting time to about 10 minutes
  • If samples are not fully clotted before being spun, they can continue to clot as they are introduced to the analyzer; this can result in aspiration errors or erroneous results due to fibrin strands
  • Clots should be removed and samples re-spun before introducing to an analyzer
  • Where possible, plasma samples (sodium or lithium heparin tubes) can be used as they contain an anticoagulant to prevent clotting
• Diluted specimen
  • Dilution of the specimen can be the result of improper collection (e.g., saline or other products from collection above IV lines) or due to adulteration
  • These specimens will generally show decreased results due to a dilutional effect
  • Serum/plasma may appear very pale, and the ratio of red blood cells to plasma will be off (significantly more plasma than red blood cells)
  • Multiple different results may be affected (e.g., chemistry and hematology results, multiple analytes, etc.)
  • Certain tests may be affected more depending on the diluting material
    • Contamination from heparinized lines will falsely prolong coagulation results
• Contaminated specimen
  • EDTA contamination
    • Due to improper collection order (e.g., collection of lavender top EDTA tubes before chemistry tubes)
      • Falsely increased potassium (often >10 mmol/L)
      • Falsely decreased calcium (often <0.50 mmol/L), magnesium, and alkaline phosphatase (ALP)
  • Lithium heparin contamination
    • Falsely increased lithium
    • Sodium heparin should be used for samples requiring lithium measurement
• Old or unspun specimens
  • The stability of analytes can change as specimens age, especially when red blood cells are not separated from serum/plasma
  • Samples should be spun as soon as possible; if a separator gel is not present in the tube, plasma/serum should be aliquoted to a new tube
  • Falsely increased potassium (as a major intracellular cation, potassium leaks from red blood cells over time or when cells are damaged)
  • Falsely decreased glucose (as glucose is taken up by cells and used for cellular respiration over time as the sample sits)
• Biotin
  • Biotin (also known as Vitamin B7, Vitamin H, or coenzyme R) may interfere with biotin-based immunoassays, causing false positive results