Preanalytical Errors in Blood Collection

Preanalytical means everything that happens to a sample before the lab tests it: preparing the patient, identifying them, drawing the blood, and handling and moving the tube. The lab's machines are checked constantly. The person holding the needle is where most errors enter. A bad sample does not always look bad, and a doctor may treat a result that was never true. This guide explains how each error changes a result, so you can prevent it and recognize it when the lab calls. Your lab's written procedure comes first.

What You Will Be Able to Do

• Explain why the order of draw exists, and what each kind of carryover does to a result.
• Fill a light blue tube correctly and work out its minimum fill.
• Find the cause of hemolysis in your own technique.
• Spot a result pattern that points to a collection error.
• Respond correctly when you find a mistake, including one of your own.

The Most Dangerous Error: Wrong Blood in Tube

Wrong blood in tube means the label says one patient and the blood belongs to another. The sample looks perfect, so nothing in the lab stops it. One patient may get treatment meant for someone else, and the other patient's real problem goes unseen. In a blood bank sample, it can lead to a fatal transfusion reaction.

These errors usually come from small shortcuts:

• Printing labels for several patients and carrying them together.
• Filling in a name from memory instead of asking.
• Labeling at the counter instead of at the bedside.
• Asking "Are you Mr. Hall?" and getting a nod from a patient who is confused or hard of hearing.

The cure is the same every time. Have the patient state their name and date of birth, check them against the wristband and the order, draw, and label before you leave them. Take one patient's labels at a time.

If a patient cannot tell you who they are and has no wristband, stop. Ask the nurse to identify them according to your facility's procedure. A family member's word or a name on a door is not identification.

Warning: Never relabel a tube, peel a label off, or "fix" a mismatch at the counter. If you doubt the identity on a tube, report it. The lab will usually ask for a new draw.

Why the Order of Draw Matters

The order of draw exists for one reason: a tiny amount of additive can ride on the needle from one tube into the next. Each tube's additive is chosen to do a job, and that same additive can ruin a different test.

Now the order makes sense:

1. Blood culture bottles come first, because they must stay sterile.
2. Light blue comes before anything with a clot activator or heparin, because clotting tests are so easily disturbed. CLSI allows only a culture bottle, a glass serum tube with no additive, or a plastic serum tube with no clot activator ahead of it.
3. Serum tubes (red, gold) come next.
4. Green (heparin) comes after serum tubes, so that heparin does not reach them.
5. Lavender or pink (EDTA) comes late, because EDTA does the most damage to chemistry tests.
6. Gray comes last, because its additives upset many other tests.

For a tube not on the chart, ask whether its additive could change the next tube's test. Your lab's test directory will tell you where it goes.

Stopping Backflow

Carryover can also travel through the patient. If blood in a tube touches the needle while the tourniquet is released, a small amount can flow back. Keep the arm angled down and the tube below the site, with the stopper end up. Do not let the blood in the tube touch the stopper during the draw.

Never Pour Tubes Together

Do not pour blood from one tube into another, even if the tubes match. Pouring from a lavender tube into a gold one adds EDTA directly. Pouring two matching tubes together doubles the additive. Two partly filled light blue tubes cannot be combined into one good tube. If a tube is short, draw a new one.

Fill and Mix: The Light Blue Tube

Light blue tubes depend on an exact ratio of 9 parts blood to 1 part citrate. Too little blood leaves extra citrate. That extra citrate binds the calcium the lab adds during testing, so the sample takes too long to clot. A patient's PT or PTT looks too long, and a provider may change a blood thinner dose because of it.

Most labs need a light blue tube at least 90 percent full, and the fill line marks this.

Worked example. A tube is labeled 2.7 mL. 2.7 x 0.90 = 2.43 mL. Anything under about 2.4 mL is short and will likely be rejected. Do not guess by eye. Check the fill line on the tube.

Air in butterfly tubing takes up vacuum. If light blue is your first tube on a butterfly, draw a discard tube first, either a light blue or a tube with no additive. It does not need to be full. It only clears the air.

A very high red cell count also changes the ratio, because there is less plasma in the blood. If the lab flags this for a patient, follow its directions.

Mix right away for every additive tube. A lavender tube that was not inverted forms tiny clots, and the CBC is lost. Follow the tube maker's number of inversions.

Hemolysis: The Most Common Reason Samples Are Rejected

Hemolysis means red blood cells have burst and spilled their contents into the serum or plasma. Reviews of lab data keep finding it at the top of the rejection list, far ahead of other causes. Red cells are full of potassium, so hemolysis can raise a potassium result falsely. It also raises other results, such as AST and LDH, and color from the broken cells can interfere with some tests.

Most hemolysis comes from collection. Work out which step caused yours.

Hemolysis can also happen inside the patient. If a careful redraw is hemolyzed too, tell the lab, because that may be a real medical finding.

Tourniquet and Fist Errors

Blood pools under a tourniquet. Water leaves the vein, so large molecules such as proteins, cholesterol and some enzymes concentrate. Pumping a fist pushes potassium out of muscle cells and into the blood. Both errors raise results falsely, with no sign in the tube.

Example. A patient pumps her fist for a full minute because a friend told her it helps. Her potassium comes back high, and she gets called back for a redraw, a worry and a delay. Your one line, "Just make a loose fist and hold still," prevents this.

Patient Preparation and Timing

Some errors happen before you arrive.

• Fasting. A test ordered fasting needs the patient to have had nothing but water for the time the order states. For fasting glucose this is at least 8 hours. Ask what they ate and when, and write it down if your procedure says to.
• Timing. Some results change by time of day, and drug levels depend on the time of the last dose. Collect at the ordered time and record the real time.
• Posture. Going from lying down to standing moves water out of the blood, so proteins and substances bound to them rise. Ask if your lab wants the patient seated for a few minutes first.
• Exercise. Hard exercise right before a draw can raise muscle enzymes and other results.

If the patient was not prepared, do not just draw and hope. Ask the nurse or the ordering office whether to go ahead, and note it if they say yes.

When the Lab Calls: Reading the Pattern

Lab staff often see a problem from the result pattern alone. Knowing these patterns helps you find your own errors.

When Something Goes Wrong

You will make an error at some point. What you do next matters more.

1. Stop and speak up. Tell the nurse or your lead right away. A mistake reported in 5 minutes may cost a redraw. A hidden mistake can harm a patient.
2. Do not repair the sample. No relabeling, topping off or pouring.
3. Recollect if the lab says so. Explain to the patient honestly why you are back.
4. Report it as your procedure directs.
5. Find the cause. Ask what the lab saw, and change the habit.

Many labs track rejection rates for each collector. It helps to know your own number.

Worked example. You drew 900 samples last quarter, and 18 were rejected for hemolysis. 18 / 900 = 0.02, or 2 percent. Compare that with your lab's target. If most of the 18 came from butterfly draws, look at your needle size and tube choice first.

Common Mistakes

Check Your Understanding

1. A lab calls about a patient's potassium of 7.8 and calcium that is almost too low to measure. The patient looks well. What collection error fits, and what do you check?

EDTA carryover fits, because EDTA adds potassium and binds calcium. Check whether the lavender tube was drawn before the chemistry tube, or whether blood was poured from one tube into another. A redraw in the right order is needed.

2. You use a butterfly for a PT/INR only. Your light blue tube fills to about 80 percent, then stops. Can you send it?

No. It is short, and the extra citrate would falsely lengthen the result. Draw a new tube, and use a discard tube first to clear the air.

3. You get back to the lab and notice that one tube has no label, but you think you know whose it is. What do you do?

Do not label it. Tell your lead or the nurse. The sample cannot be trusted, and the patient will likely need a new draw.

4. A careful redraw is hemolyzed again, with a good vein and the right needle. What could this mean?

Hemolysis may be happening inside the patient's body. Tell the lab, so they can tell the provider.

Key Takeaways

• Most errors happen before the lab ever sees the sample, and many leave no visible sign.
• Wrong blood in tube looks perfect. Identify, draw and label at the patient's side, one patient at a time.
• The order of draw exists to stop additive carryover, and each tube's position has a reason.
• Fill light blue tubes to at least 90 percent, and never combine or top off tubes.
• Hemolysis is the top reason for rejection, and most of its causes are in your technique.
• Report mistakes right away. Never repair a sample.