Hemolysis vs Clotted Samples: A Practical Guide to Blood Collection and Tube Handling

Hemolysis vs
Clotted Samples

A practical guide for blood collection, tube handling, and accurate laboratory results.

Hello, I’m Christine from DMS Care Training Center.

DMS is a Healthcare Career School located in Carrollton, Texas. We provide hands-on training programs including CNA, Medical Assistant, Phlebotomy Technician, Patient Care Technician, and more. At DMS, we focus on practical skills that students can apply in real healthcare settings.

Why This Topic Matters

Redraws are one of the most common and frustrating outcomes in blood collection. In many cases, a sample may be called “clotted,” but the actual issue may be hemolysis. Hemolysis and clotting are different specimen problems, and each one affects laboratory testing in a different way.

Understanding the difference helps healthcare workers collect better samples, reduce repeat blood draws, prevent delays, and support accurate patient care.

Key point: Hemolysis is red blood cell damage. Clotting is fibrin or clot formation. Both can make a specimen unsuitable for testing.

Hemolysis

Hemolysis means the rupture of red blood cells. When red blood cells break open, they release hemoglobin and intracellular contents such as potassium, LDH, AST, magnesium, and phosphate into the plasma or serum.

This changes the chemical composition of the specimen and may cause inaccurate or misleading laboratory results.

Typical Appearance of Hemolysis

After centrifugation, plasma or serum may appear pink to red. There is usually no visible clot, strand, or solid material.


Collection Causes

Mechanical Stress

Hemolysis may occur from using a needle that is too small, pulling a syringe plunger too forcefully, vigorous shaking, prolonged tourniquet use, or difficult venipuncture with multiple attempts.

Handling Causes

After Collection

Delayed processing, freezing and thawing, excessive heat exposure, or rough transport such as strong pneumatic tube force may also damage red blood cells.

Why hemolysis is a problem: Red blood cell contents leak into the plasma or serum. This may falsely increase potassium, LDH, AST, magnesium, phosphate, and other values. Hemoglobin pigment can also interfere with some chemistry tests.

Clotted Samples

Clotting means fibrin and cellular material have formed inside the sample. This is especially a problem in tubes that contain anticoagulants, such as EDTA, sodium citrate, or heparin tubes.

These tubes are designed to prevent blood from clotting. If the tube is not mixed properly and immediately, the anticoagulant may not contact the blood evenly, allowing clots to form.

Appearance

What You May See

Visible clumps, fibrin strands, or irregular solid material may be seen inside the tube. Sometimes small clots may not be obvious until the lab checks the sample.

Common Causes

Mixing Problems

Failure to invert the tube immediately, insufficient mixing, underfilled tubes, delayed processing, or poor specimen handling can lead to clot formation.

Why clotting is a problem: A clotted sample may trap cells and platelets, causing inaccurate cell counts. It is especially unsuitable for hematology tests such as CBC and may also affect coagulation testing.

Key Difference Between Hemolysis and Clotting

Condition What Happens Common Practical Cause Why It Matters
Hemolysis Red blood cells rupture and release contents into plasma or serum. Mechanical stress during collection or handling. May falsely change chemistry values such as potassium, LDH, AST, and others.
Clotting Fibrin and cellular aggregates form inside the tube. Inadequate mixing with anticoagulant. May cause inaccurate cell counts and make hematology samples unacceptable.

Common Blood Collection Tubes: Additives and Purpose

Each blood collection tube has a different additive and purpose. Using the correct tube and mixing it correctly is important because the additive helps preserve the sample for the intended test.

Blood Culture / Yellow

Additive: SPS or culture media, depending on the system.

Purpose: Used to detect microorganisms in the blood.

Improper collection can lead to contamination or inaccurate culture results.

Light Blue

Additive: Sodium citrate.

Purpose: Used for coagulation tests such as PT and aPTT.

Must be filled properly because the blood-to-additive ratio is important.

Red / Gold SST

Additive: No additive, clot activator, or clot activator with gel separator.

Purpose: Used for serum testing, including many chemistry, hormone, and serology tests.

Hemolysis can interfere with many serum chemistry results.

Green

Additive: Heparin.

Purpose: Used for plasma chemistry testing and some stat chemistry tests.

Mix gently to prevent clotting without damaging red blood cells.

Lavender / Pink

Additive: EDTA.

Purpose: Used for hematology testing such as CBC, and pink tubes are often used for blood bank testing.

Clots in EDTA tubes can make CBC results inaccurate or unacceptable.

Gray

Additive: Sodium fluoride and potassium oxalate.

Purpose: Used for glucose testing and blood alcohol testing.

Proper handling helps preserve glucose and prevent inaccurate results.

Important: Tube additives are designed for specific tests. Using the wrong tube, wrong order, or poor mixing technique can affect the specimen before it even reaches the laboratory.

Proper Tube Mixing

According to CLSI-based practice and standard laboratory protocols, tubes with additives should be gently mixed immediately after collection. Mixing allows the additive to contact the blood evenly.

  1. Invert tubes immediately after collection
  2. Use a full 180° turn and return
  3. Follow the recommended number of inversions
Do not shake tubes. Shaking can damage red blood cells and contribute to hemolysis. Gentle inversion helps prevent clotting without causing unnecessary cell damage.

How to Prevent Hemolysis and Clotting

Prevent Hemolysis

Protect Red Blood Cells

Use the correct needle size, avoid excessive suction, do not shake tubes, avoid prolonged tourniquet time, and handle specimens gently during transport and processing.

Prevent Clotting

Mix Additives Correctly

Fill tubes properly, invert tubes immediately after collection, follow recommended inversion guidelines, and avoid delays in processing anticoagulated samples.

Patient safety point: Preventing hemolysis and clotting reduces redraws, prevents delays, and helps avoid inaccurate clinical decisions.

Why This Matters in Real Practice

Both hemolysis and clotting can alter test results, delay diagnosis, and require repeat blood collection. A redraw may seem like a small issue, but for patients it can mean more discomfort, longer wait times, and delayed treatment decisions.

Good specimen quality begins at the bedside or collection chair. Proper technique during collection, tube filling, mixing, labeling, transport, and processing directly affects the reliability of laboratory results.

What Students Learn at DMS

In our Phlebotomy Technician and Medical Assistant programs, students learn how to collect and handle blood specimens safely and accurately.

  • Difference between hemolysis and clotted samples
  • Common tube additives and their purpose
  • Proper tube inversion and specimen mixing
  • How collection technique affects lab results
  • Specimen handling, transport, and patient safety
  • How to reduce redraws and pre-analytical errors

Accurate laboratory results begin with accurate blood collection.

Healthcare Career Starts Here

DMS teaches practical skills students need to collect, handle, and protect specimens safely and accurately.

Contact: admin@dmscare.org · 469-237-9852

Visit the DMS Website