accurately completed request forms,
the collection of specimens by the correct technique at the appropriate time,
Table 29.1 Some extra-laboratory factors leading to erroneous results
Cause of error
Some possible consequences
Patient not fasting
High plasma triglyceride and glucose
Keeping blood overnight before sending it to the laboratory or refrigerating blood sample
Haemolysis of blood
As above, lower plasma ALP
Prolonged venous stasis during venesection
High plasma protein, total calcium and cholesterol
Taking blood from an arm with an infusion running into it
Dilution of blood constituents such as electrolytes and glucose
Putting blood into wrong vial or tipping it from one vial into another
Blood for glucose not put into fluoride
Low blood or plasma glucose
Delay in analysing blood gases
Low bicarbonate concentration
Failure to keep sample cool or delay separating and freezing plasma
Incorrect anticoagulant
e.g. gut peptide hormones falsely low if no protease inhibitor used
Palpation of prostate by rectal examination, passage of catheter, enema in last few days
High tartrate-labile acid phospatase and PSA
Inaccurately timed urine collection
Poorly timed 24-h urinary excretion values
Abnormal renal clearance values
Urine collections without preservative
Falsely low result, e.g. urea or calcium
Loss of stools during faecal fat collection
Falsely low faecal fat results (test now rarely done)
ACTH, adrenocorticotrophic hormone; AST, aspartate transaminase; ALP, alkaline phosphatase; EDTA, ethylenediamine tetra-acetic acid; LDH, lactate dehydrogenase; PTH, parathyroid hormone; PSA, prostate-specific antigen.
correctly labelled specimens,
appropriate laboratory liaison,
speedy delivery to the laboratory.
hospital case number, and/or healthcare number,
surname and first name(s), correctly and consistently spelt,
date of birth, rather than age.