Common Mistakes in Blood Tube Usage and How to Avoid Them
, by Andrew Odgers, 9 min reading time
Pre-analytical Quality
Common Mistakes in Blood Tube Usage and How to Avoid Them
Pre-analytical errors in blood collection account for the majority of laboratory errors that lead to incorrect or uninterpretable results. Most of these errors occur at the tube selection or handling stage rather than in the laboratory itself. This guide identifies the most common blood tube mistakes, explains their consequences, and gives the straightforward correction for each.
Tube selection errors
The wrong tube for the test requested
Using the wrong tube is the most fundamental error in blood collection. The consequences range from sample rejection to clinically significant result errors.
- Using an EDTA tube instead of a citrate tube for coagulation tests. EDTA carryover into a citrate tube produces falsely prolonged coagulation times, but drawing coagulation tests into an EDTA tube is more fundamental: the wrong anticoagulant produces invalid coagulation results entirely. EDTA chelates calcium differently to citrate and at a different ratio. Always use a light blue sodium citrate tube for PT, APTT, fibrinogen, and D-dimer.
- Using an SST or heparin tube for a lithium level. Lithium heparin tubes contain lithium; SST tubes contain a silicone clot activator that may interfere with some assays. For plasma lithium measurement, use a plain or EDTA tube as specified by your laboratory. Using a lithium heparin tube for a lithium level produces a falsely elevated result.
- Using any tube other than a grey fluoride oxalate tube for glucose or lactate. In a plain, SST, or heparin tube, red blood cells continue to consume glucose after collection (glycolysis). This can reduce glucose values by up to 10 percent per hour at room temperature. A fluoride oxalate tube inhibits glycolysis and is required for accurate glucose and lactate measurement.
- Using a standard tube for trace element analysis. Standard blood collection tubes contain sufficient metal contamination to interfere with zinc, copper, lead, and manganese assays. Use a dark blue or specific trace-element tube manufactured to be metal-free for these analyses.
Filling and handling errors
Problems after the correct tube is selected
Errors at the filling and handling stage frequently invalidate correctly selected tubes.
- Underfilling the citrate coagulation tube. The sodium citrate additive is calibrated for a specific 1:9 citrate-to-blood ratio. Underfilling increases the effective citrate concentration, which chelates excess calcium and produces falsely prolonged PT, APTT, and other coagulation times. Most laboratories specify a minimum fill of 90 percent of the stated volume. Never submit a light blue tube that is less than approximately nine-tenths full.
- Not inverting tubes immediately after filling. Anticoagulated tubes must be inverted immediately and the specified number of times to mix blood with the additive. Clot formation in an EDTA or heparin tube, or incomplete activation in an SST tube, produce invalid results and rejected samples. Invert gently; vigorous shaking causes haemolysis.
- Vigorous shaking rather than gentle inversion. Shaking a tube haemolyses red blood cells, releasing intracellular contents including potassium, LDH, and haemoglobin into the serum or plasma. Haemolysed samples interfere with many assays and may be rejected by the laboratory. Always invert gently end-over-end the specified number of times.
- Wrong order of draw. Additive carryover from an earlier tube into a later tube, or tissue thromboplastin into a coagulation tube drawn first, can produce significant result errors. Follow the standard order: blood cultures, citrate, SST, heparin, EDTA, fluoride oxalate.
- Delayed or incorrect transport. Many analytes degrade after collection. Coagulation samples should reach the laboratory within 4 hours of collection. Glucose stabilised in fluoride oxalate is more forgiving but should still be processed promptly. Blood gases require immediate analysis. Know the stability windows for the tests requested.
- Incorrectly labelled or unlabelled tubes. A correctly collected sample in the wrong patient's label is a patient safety incident. Always label tubes at the bedside immediately after collection, confirming the patient's identity against the label before writing it.
Quality tubes for quality samples
Blood collection tubes with reliable fill volumes and additives
Charles Medical supplies precision blood collection tubes with accurate fill volumes and verified additive content. Next-day UK delivery.
For the order of draw reference, see The Correct Order of Draw in Blood Collection.
Part of the hub
Back to the Blood Collection Tubes Knowledge Hub
This article is part of our complete blood collection tube knowledge base, covering tube types, colours, additives, order of draw, pre-analytical errors, disposal, and everything phlebotomists and laboratory staff need to know.
Keep reading
Related guides in this hub
The Correct Order of Draw in Blood Collection covers the sequencing errors in detail. Understanding Blood Tube Colours and What Each One Means provides the colour reference that prevents wrong-tube selection. And Why the Right Tube Matters for Each Blood Test explains the downstream consequences of the errors described here.
Frequently asked
Blood tube error questions answered
What happens if I underfill a citrate tube?
Underfilling a citrate coagulation tube increases the citrate-to-blood ratio, causing excess calcium chelation that falsely prolongs coagulation times. PT, APTT, and fibrinogen results will be inaccurate. Most laboratories will reject a citrate tube filled to less than 90 percent of its stated volume. Recollect the sample.
How do I know if a sample has haemolysed?
Haemolysed serum or plasma appears pink to red rather than clear yellow or straw-coloured. Mild haemolysis may not be visible but is detected by the analyser. Haemolysis elevates potassium, LDH, AST, and total bilirubin, and interferes with many photometric assays. The laboratory will report haemolysis when detected and may reject the sample depending on the degree and the assay affected.
Can I use an expired blood collection tube?
No. Expired tubes may have lost vacuum, which prevents complete filling and alters the additive-to-blood ratio. The additives may also have degraded. Remove expired tubes from stock and do not use them.
What should I do if I realise I used the wrong tube?
Do not submit the sample without flagging it to the laboratory. Contact the laboratory to advise which tests were requested and which tube was used. In many cases the laboratory can advise whether the sample is acceptable for any of the requested tests or whether recollection is needed. Document the error and follow local incident reporting procedures.