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:
- Green 21G needle
- Blue 23G butterfly
The order of the draw should be:
- Blood culture
- Serum/serum gel
- Citrate
- Lithium Heparin
- EDTA
- Blood Transfusion EDTA
- 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.
| 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 |
Interferences in results of urine catecholamines
Requests for urine and plasma catecholamines and metadrenalines 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
| 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
- Lenders JW, Eisenhofer G, Mannelli M, Pacak K. Lancet 2005;366:665-675.
- 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.
- 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.
- Table 4, Drugs that may cause false positive elevations of plasma and urinary catecholamines or metanephrines - Endotext - NCBI Bookshelf (nih.gov)
- 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
- A van Berkel et al. Biochemical diagnosis of phaeochromocytoma and paraganglioma. European Journal of Endocrinology (2014) 170, R109–R119