Haematology - Common Causes of Spurious Results

Problem	Common Causes	Affected Analyte
Delay in processing	Overnight storage >6 hour delay in separation	Increased MCV Prolonged clotting times or shortening of APTT ratios
Inappropriate timing of sample	Lack of knowledge	For example, anti Xa for monitoring clexane
Incorrect storage	Storing unseparated sample in the fridge	Unreliable clotting times Falsely low plasma viscosity
Clotted EDTA/citrate sample	Incorrect mixing	Unreliable FBC, clotting and other tests
Partially clotted EDTA samples	Incorrect mixing	Unreliable FBC, clotting and other tests False positive reactions in blood transfusion
Haemolysis	Expelling blood through needle Vigorous shaking Extreme temperature Difficult venipuncture	Shortened clotting times Possible raised D Dimer Falsely low platelet count Unreliable results for other tests Can mask the presence of antibodies in blood transfusion
Lipaemia	Recent fatty food intake	Increased Hb and MCHC Unreliable clotting tests Causes problems in compatibility and antibody screening
Inappropriate Collection Site	Sample taken from drip arm	Unreliable clotting times Unreliable FBC and other tests Causes problems in compatibility and antibody screening
Underfilled sample container	Difficult venipuncture	Prolonged/unreliable clotting times
Effect of high PCV		Unreliable clotting results
Incorrect container or anticoagulant	Incorrect container selected	Unreliable test results   May be unsuitable to be processed on autoanalysers

Also, please be careful about which tests and investigations you requests to ensure that the result of the test answers your question.

Requesting Further Tests

If further tests are required on a sample which has already been sent to the laboratory then please telephone the laboratory to see if there is sufficient sample and that the sample is not too old.

In addition to the above any change to a patient's blood transfusion history may alter the validity of a sample held in the laboratory. Please contact Blood Bank.