Factors affecting the results or processing of tests

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Here are some of the factors which could affect the results or processing of blood counts. This is not an exhaustive list. There may be other factors affecting the reporting of results which are not listed.

Also see a list of factors affecting all sections of the haematology department.

Test Factors affecting result/processing Outcome
FBC Small sample

Paediatric- minimum required sample volume – 500µl – otherwise comment ‘Insufficient’

Neonate- minimum required sample volume – 160µL- otherwise comment ‘Insufficient’

Adult – minimum required sample volume – 1.5ml – otherwise comment’ Insufficient’

FBC and ESR Small sample

Paediatric – separate sample ESR.

FBC + ESR requires 2.5ml in FBC tube otherwise will be reported as ‘Insufficient’

FBC and Film Old sample (greater than 24 hours)

FBC would not be processed and comment – ‘Too old for analysis’

Film would be reported as – ‘Too old for morphology’

FBC, ESR and Retic Clotted Sample, or severe case of Cold Agglutination

Would not be processed

Severe cases of Cold Agglutination the sample must be sent warm (37°C) to the laboratory

FBC EDTA may cause clumping of platelets This would result in a falsely low platelet count – laboratory will check a blood film and ask for citrated (Coag) sample to attempt an accurate measurement of the platelets
CSF Contaminated with red cells Would process – appropriate comment will be added
Bone marrow smears Not enough marrow material to perform stains on Could not perform stains – repeats would be requested


(Last reviewed November 2019)