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Study Reinforces Proper Tube Filling

Underfilled tubes wreaking havoc on test results

by Dennis Ernst • December 04, 2020


gloved hand holding blood tube

Researchers in Germany have published the results of their study on the impact of underfilling heparin tubes on test results.

In the study, over 74,000 lithium heparin tubes were either filled or 50 percent underfilled, then tested for potassium, sodium, chloride, LD, CK, total cholesterol, and  hemolysis, icterus, and lipemic indices.

Underfilling demonstrated consistently higher LD and K results and showed greater hemolysis. Other analytes remained unchanged. The authors also concluded the practice of underfilling tubes results in a higher velocity of aspiration for a higher proportion of the sample collected than for fully filled tubes where the velocity of aspiration decreases as the tube fills (and the vacuum is exhausted). The higher relative velocity of aspiration likely contributes to the higher hemolysis rates, and the higher LD and potassium levels, since red blood cells have high concentrations of both analytes. Read the abstract.

This study reinforces prior studies with similar results. A study published in 2006 showed lithium heparin tubes filled less than half significantly impact results for ALT, AST, amylase, lipase, and potassium.1 The excess heparin that results from underfilling was also reported to cause falsely lower sodium levels. Other researchers, including Phlebotomy Today Editor, Dennis J. Ernst,  found ALT, amylase, AST, lipase, potassium, troponin, CK and GGT results significantly changed as compared to completely filled tubes.2-4  


  1. Lippi G, Salvagno G, Montagnana M, Franchini M, Guidi G. Phlebotomy issues and quality improvement in results of laboratory testing. Clin Lab 2006;52(5-6):217-30.
  2. Donnelly JG, Soldin SJ, Nealon DA, Hicks JM. Is heparinized plasma suitable for use in routine biochemistry? PediatrPathol Lab Med. 1995 Jul-Aug;15(4):555-9.
  3. Tietz Guide to Clinical Laboratory Tests WB Saunders, St. Louis, MO (2006).
  4. Lippi G, Avanzini P, Cosmai M, Aloe R, Ernst D. Incomplete filling of lithium heparin tubes affects the activity of creatine kinase and gamma-glutamyltransferase. Br J Biomed Sci 2012;69(2):67-70.


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