Key Factors That can Affect Results
Common causes of spurious results due to incorrect collection or storage
Note: Common analytical interferences are screened for and if detected no results will be reported for that analyte.
Problem |
Cause(s) |
Affects |
Delay in processing |
|
Increases potassium, & phosphate |
Incorrect storage |
|
Increases potassium Decreases bicarbonate |
Haemolysis |
|
Increases potassium, phosphate, bilirubin.
Also increases AST, LDH, CK and decreases Troponin T & glucose |
Incorrect sample site |
|
Increased drip analytes e.g. glucose, potassium etc. Dilutional effect lowers other analyte concentrations |
Incorrect sample tube |
|
Increased potassium Decreased calcium, alkaline phosphatase, iron, magnesium |
Lipaemia (fatty sample) |
|
Decreases sodium Affects other analytes if severe |
Analytes requiring special conditions
Analyte |
Sample Tube |
Special Conditions |
ACTH |
Adult Purple Top Tube (EDTA) |
Send to lab ASAP (within 15 mins). Transport on ice if possible. |
Ammonia |
Adult Purple Top Tube (EDTA) or Red Top (Paeds) |
Send to lab ASAP (within 15 mins). Notify lab before taking. Avoid haemolysis. |
Calcitonin |
Adult Red or Yellow Top Tube
|
Send to lab ASAP (within 15 mins). Transport on ice if possible. |
Glucose |
Adult Grey Top Tube (Fluoride oxalate) or Yellow Top (Paeds) |
Yellow/red top tubes are acceptable from A&E as processed within 2 hours |
Gut hormone profile |
Special green top tubes containing protein inhibitor |
Before taking contact Biochemistry who will provide tubes and ice |
Homocystine |
Adult Red or Yellow Top Tube |
Send to lab ASAP (within 15 mins). Transport on ice if possible. |
Insulin/C-peptide |
Adult Grey Top Tube (Fluoride oxalate) or Yellow Top (Paeds) |
Send to lab ASAP (within 15 mins). Transport on ice if possible. Insulin is only sent for analysis if glucose < 2.5 mmol/L (unless specifically requested) |
Lactate |
Adult Grey Top Tube (Fluoride oxalate) or Yellow Top (Paeds) |
Send to lab ASAP (within 15 mins). Notify lab before taking. Avoid haemolysis. |
PTH |
Purple Top Tube (EDTA) |
Stable for 8 hours in EDTA |
Renin |
Adult Purple Top Tube (EDTA) or Red Top (Paeds) |
Send to lab ASAP (within 15 mins). Do not use ice. Take sample after 15 mins recumbency. |
CSF Bilirubin (Xanthochromia) |
1 mL (last sample) required Serum required for bilirubin and total protein |
Send to lab ASAP (within 15 mins). Protect from light. Do not use airtube. |
Commonly Encountered Analytical Interferences (in Bold) or Biological Actions
Analyte |
Drug or Substance Interfering |
Effect |
Alkaline Phosphatase |
· Anticonvulsants, barbiturates, oral contraceptive · EDTA contamination |
Up Down |
Calcium |
· Prolonged tourniquet use, Vit D, bendrofluazide · EDTA or citrate contamination, citrated blood |
Up Down
|
Cholesterol |
· Oestrogens |
Down |
Creatinine |
· High bilirubin (icterus) and lipid (lipaemia) |
Down |
Gamma GT |
· Anticonvulsants, barbiturates, alcohol |
|
Glucose |
· Frusemide, thiaxides, corticosteroids, stress
|
Up |
Potassium |
· Insulin, corticosteroids, loop/thiazide diuretics · K+ sparing diuretics, ACE inhibitors · Haemolysis, EDTA contamination, excess storage |
Down Up Up |
Prolactin |
· Oestrogens, MAO inhibitors, cimetidine |
Up |
Sodium |
· Lithium · Diuretics, carbamazepine, fluoxetine, lipaemia |
Up Down |
Thyroxine |
· Amiodarone, pregnancy · Oestrogens · Phenytoin, corticosteroids, heterophilic antibodies |
Up or Down Up Down |
- Created on .
- Last updated on .