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Sample requirements

Information on how to perform venepuncture, types of anticoagulant and sample volume requirements and on drug interferences in plasma and urine catecholamine, and metadrenaline testing.

How to perform venepuncture

Remember to wash your hands before and after taking blood samples.

The blood collection needles used are:

  1. Green 21G needle
  2. Blue 23G butterfly 

The order of the draw should be:

  1. Blood culture
  2. Serum/serum gel
  3. Citrate 
  4. Lithium Heparin
  5. EDTA
  6. Blood Transfusion EDTA
  7. Fluoride

Why was a blood sample rejected?

Sample rejections are preventable:

  • samples should be ordered via the ICE system, ensuring that the print is readable
  • aim to use good patient identification
  • make sure you use blood bottles and safety needles, and ensure bottles are the right size for the patient - use adult bottles for adults, for example
  • plan - use the correct order of draw, and ensure bottles are filled to the line
  • look and think about the time that the tourniquet has been in-situ - the maximum time is 2 minutes (otherwise the sample will hemolyse and then be rejected)
  • ensure that you only label at the bedside, ensuring the right patient and the right samples, and that all demographics are correct on every sample
  • send to the labs as soon as possible

Following these guidelines will ensure your samples are of optimum quality and that they will not be rejected. 

If you have any questions or require further information, please contact Kathryn Osbyrne (Clinical Skills) via telephone: 01226 435057

The table below outlines the different types of anticoagulant and sample volume requirements for the tests listed in the test repertoire table. The information in the test repertoire table refers to one adult or one paediatric sample unless stated otherwise.

Anticoagulant and sample volume requirements
Colour reference in the test repertoire table Anticoagulant used Standard bottle volume (Adult) Paediatric bottle volume
Red K-EDTA (Potassium-ethylenediaminetetraacetic acid) 4.0ml 1.2ml
Brown None (gel used to separate red cells from serum) 4.9ml 1.1ml
Green Trisodium citrate 4.3ml 1.4ml
Yellow Fluoride 4.9ml or 2.7ml 1.1ml
Orange Lithium heparin 9.0ml 1.1ml

Requests for urine and plasma cats are frequently made in the investigation of suspected phaeochromocytoma. However, these analyses (in both sample types) may be subject to interference from a relatively large number of medications. Please see the table below for further details and contact the laboratory if you wish to discuss anything.

  • A – Adrenaline
  • DHPG – Dihydroxyphenylglycol.4-6
  • MA – Metadrenaline
  • NA – Noradrenaline
  • NMA – Normetadrenaline
  • VMA – 4-hydroxy-3-methoxymandelic acid
Anticoagulant and sample volume requirements

Class of drug and examples

Mechanism of action

Effect

References
a-adrenergic receptor blockers (non-specific):
Phenoxybenzamine		 Blocks pre-synaptic a2-adrenoceptors, and attenuates alpha receptor feedback inhibition Increases plasma NA, NMA & urinary NA, NMA and VMA 1, 3, 4, 5, 6
a-adrenergic receptor blockers (selective):
Doxazosin, Indoramin,
Prazosin, Terazosin		 Reflexive sympathetic activation Increases urinary NA 3, 4, 6
Beta-adrenergic receptor blockers:
Atenolol, Labetolol,
Metoprolol, Propranolol Oxprenolol		 Not applicable  Increases plasma MA & urinary NA, A, NMA, MA 3, 4
Calcium channel blockers:
Amlodipine, Diltiazem,
Nifedipine, Verapamil		 Increases sympathetic activation Increases plasma & urinary NA and A 1, 3, 4
Centrally acting anti-hypertensive drugs:
a-methyldopa		 Metabolised by enzymes that also convert catecholamines Increased plasma A and NA & urinary A and NA 1
Dopaminergic drugs:
Carbidopa, Levodopa		 Metabolised by enzymes that also convert catecholamines Increased plasma A and NA & urinary A and NA, MA and NMA 1, 4, 6
Monoamine oxidase inhibitors (MAOI):
Isocarboxazid, Phenelzine,
Tranylcypromine, Selegiline		 Blocks conversion of NA and A to DHPG Up to 5 fold increase in plasma & urinary NMA and MA, some potential increase in NA and A 1, 2, 4, 5, 6
Selective noradrenaline reuptake inhibitors:
Venlafaxine		 Inhibits NA and A re-uptake Increases plasma & urine NA, A and NMA 2, 6
Selective serotonin reuptake inhibitors:
Citalopram, Fluoxetine, Sertraline		 Blocks NA re-uptake Increase plasma & urine NA, A and NMA 2, 6
Stimulants:
Caffeine, Cocaine,
Nicotine, Theophylline		 Activation of adrenergic receptors Increase plasma and urinary A and NA, MA, NMA 1, 2, 4, 5, 6
Sympathomimetic factors:
Albuterol, Amphetamine,
Ephedrine, Pseudoephedrine		 Activation of adrenergic receptors Increase plasma and urinary A, NA, MA and NMA 1, 2, 3, 4, 5
Tricyclic antidepressants:
Amitriptyline, Clomipramine, Dosulepin,
Imipramine, Nortriptyline		 Blocks NA re-uptake Increase plasma and urinary NA, NMA and VMA 1, 3, 4, 5
Vasodilators:
Hydralazine, Isosorbide
Minoxidil		 Reflexive sympathetic activation Increase NA (unknown effect on MA and NMA) 4, 6

References

  1. Lenders JW, Eisenhofer G, Mannelli M, Pacak K. Lancet 2005;366:665-675.
  2. Neary NM, King KS, Pacak K. Drugs and phaeochromocytoma – Don’t Be Fooled by every Elevated Metanephrine. New Eng J Med. 2011;364:2268-70.
  3. Eisenhofer G, Goldstein DS, Walther MM et al. Biochemical diagnosis of phaeochromocytoma: how to distinguish true from false positive test results. J Clin Endocrinol Metab 2003;88:2656-66.
  4. Table 4, Drugs that may cause false positive elevations of plasma and urinary catecholamines or metanephrines - Endotext - NCBI Bookshelf (nih.gov)
  5. Lenders et al Pheochromocytoma and Paraganglioma: An Endocrine Society Pheochromocytoma and Paraganglioma: An endocrine society Clinical Practice Guideline. J Clin Endocrinol Metab, June 2014, 99(6):1915–1942
  6. A van Berkel et al. Biochemical diagnosis of phaeochromocytoma and paraganglioma. European Journal of Endocrinology (2014) 170, R109–R119