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Oxford University Hospitals NHS Foundation Trust
Clinical Biochemistry

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Causes of spurious results

The table below shows common causes of spurious results and the effects seen.

Results may not be reported if it is clear that the result is invalid. This list is not exhaustive; please contact the laboratory if in any doubt as to the validity of results. For example, methods using immunoassay can be subject to a range of interferences, including cross reactivity, for which the lab hold details.
Problem Cause(s) Effects
Delay in processing Overnight storage, delay in transport, delayed analysis within lab Potassium ↑, Phosphate ↑, Ammonia ↑, Bicarbonate ↓, BNP ↓, PTH ↓, Glucose ↓, ACTH ↓
Temperature Storage of samples overnight in fridge, cold weather Potassium ↑, Bicarbonate ↓
  Hot weather Potassium ↓
Haemolysis Poor collection technique, difficult to bleed, frozen storage, delayed transit/analysis ACE, B12, Folate, Insulin, PTH, Vitamin D, Zinc not reported. Potassium ↑, Phosphate ↑, Ammonia ↑, AST ↑, LDH ↑
Icterus Patient has liver disease ACE (not reported)
Lipaemia (turbid sample) Sample taken shortly after fatty meal Sodium ↓
Incorrect sample site Sample taken from drip arm Drip arm analytes ↑, other analytes ↓
Incorrect sample tube EDTA contamination Potassium ↑, Calcium ↓, Magnesium ↓, ALP ↓, Zinc ↓
Light exposure Inappropriate storage conditions Bilirubin ↓, porphyrins ↓
Cross-reactivity Interfering exogenous or endogenous substances ↑ or ↓, depending on methodology (most commonly affects drugs, hormones, tumour markers)