MLT GlobePre-analytical Errors in the Clinical Laboratory: Causes and Prevention
MLT Globe · 2026-10-02
Studies of laboratory quality have repeatedly shown that the pre-analytical phase – everything that happens before a sample is analysed – is where most laboratory errors occur. These errors are easy to make and easy to prevent.
Common pre-analytical errors
- Patient identification errors: the wrong patient's name on a tube. Always use two identifiers (for example, full name and date of birth) and label tubes in front of the patient.
- Wrong tube or wrong order of draw: EDTA carried into a serum tube can give falsely high potassium and falsely low calcium. Follow the order of draw.
- Under-filled citrate tubes: coagulation tubes need a 9:1 blood-to-citrate ratio. A short draw prolongs the PT and APTT.
- Haemolysis: caused by a small needle, forcing blood through a syringe, vigorous shaking or delays. It falsely raises potassium, LDH and AST.
- Clotted EDTA samples: caused by poor mixing. Platelet counts and other CBC results become unreliable. Invert gently 8–10 times.
- Prolonged tourniquet time: more than about a minute concentrates proteins and protein-bound substances.
- Drawing above an IV line: dilutes the sample and adds whatever is in the drip, such as glucose or saline.
- Delays and wrong temperature: glucose falls in unseparated blood, and some tests need ice or protection from light (for example, ammonia and bilirubin).
- Patient preparation: non-fasting samples for lipids, wrong timing for drug levels, or recent exercise.
How laboratories prevent them
- Written collection procedures and regular training for phlebotomists and nurses.
- Clear rejection criteria: unlabelled, mislabelled, haemolysed, clotted or under-filled samples.
- Haemolysis indices on chemistry analysers.
- Tracking and reviewing every rejected sample as part of quality improvement.
Test yourself
Pre-analytical questions appear in every licensing exam. Practise them in Laboratory Operations MCQs.
📱 Practise with a timer, track your score and earn certificates in the free MLT Globe app – Google Play or practise online.
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