Factors known to significantly affect performance of tests/interpretation of results - Manchester University NHS Foundation Trust

Factors known to significantly affect performance of tests/interpretation of results.

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.

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 July 2024)