In this section
| Problem | Causes | Affected analyte |
| Delay in processing | Overnight storage
>6-hour delay in separation |
Increased potassium, phosphate, LDH, AST. |
| Incorrect storage | Storing unseparated sample in the fridge | Increased phosphate and potassium
Decreased bicarbonate |
| Haemolysis | Expelling blood through needle
Vigorous shaking Extreme temperature |
Increased potassium, phosphate, LDH, AST. |
| Inappropriate Collection Site | Sample taken from drip arm | Increased drip analyte e.g. sodium, glucose
Decreased analytes – dilutional effect |
| Incorrect container or anticoagulant | No fluoride oxalate | Decreased glucose |
| K-EDTA contamination | Increased potassium
Decreased calcium, magnesium, alkaline phosphatase |
|
| Lithium heparin tube | Increased lithium |
Effect of haemolysis, lipaemia and icterus
Haemolysis, lipaemia and icterus may cause false elevations or reductions in the measured concentrations of several biochemistry analytes. The presence of haemolysis, lipaemia or icterus will be detected in the laboratory and the affected analytes will be flagged. In cases where there is significant interference, the affected analyte will not be reported. Further information can be obtained from the Duty Biochemist.
Effects of biotin
Biotin (vitamin B7) taken at high doses can potentially interfere with immunoassays as biotin is used in the detection system in many routine immunoassays. Concentrations of biotin found in daily multivitamins will have no effect, but doses of more than 5000 µg/day as a lifestyle supplement or for medical treatments could have an effect on immunoassay results. Assays that are potentially affected by biotin interference are:
- Anti-thyroid peroxidase antibodies
- B12
- CA-125
- Ca-199
- CEA
- Cortisol (immunoassay only)
- Digoxin
- Ferritin
- Folate
- hCG
- LH
- Oestradiol (immunoassay only)
- Prolactin
- Progesterone
- SHBG
To mitigate potential interference, patients taking biotin doses of more than 5000 µg should wait at least 8 hours after the last dose before a sample is taken.
For further information, please contact the Duty Biochemist within routine working hours.
Measurement uncertainty
All assays have a margin of error associated with the calculation of the numerical value. This is referred to as the measurement uncertainty and is usually expressed as a percentage of the reported figure. This calculation allows the user to understand the uncertainty of any numerical results and can be assured with 95% confidence that the true result lies plus or minus the measurement uncertainty around the reported value. Further information on the measurement of uncertainty for all our laboratory assays is available by contacting the Duty Biochemist within routine working hours.
Point of Care
The relationship between values obtained in the laboratory and POCT are established and available upon request.
(Last reviewed August 2024)