Preanalytics _

This is an essential step in ensuring the laboratory best practice that we guarantee and involves the application by health professionals of pre-analytical data indicated on analysis request forms and in the laboratory test catalogue.

 

Blood sample

 

Recommendations

• On an empty stomach (12 hours without eating)
• 24 hours without consuming alcohol
• Avoiding physical activity before taking blood samples
• After discontinuation of drugs or following a case history of drugs currently being administered
• After a rest of at least 10 minutes
• Sampling should ideally be done in a reclining position
• Tourniquet may be tightened for 30 seconds and then loosened while blood flows into the tube
• Do not “pump” with the fist (opening and closing the wrist)
• Respect the order of draw of the tubes (see information below)
• Turn the tubes upside down several times after drawing by tilting them
• Check the patient details written on the tubes and on the analysis request form

 

Nursing staff at doctors’ surgeries or in hospitals may be trained on request by the laboratory to take both capillary and venous blood samples.

 

Sample tube sequence

The order in which blood samples are taken is of capital importance in the pre-analytical phase. Failure to comply with these rules frequently results in the laboratory refusing to conduct certain analyses, especially with regard to coagulation.

The increasing use of winged (butterfly) blood collection sets for drawing blood samples requires strict compliance with these rules. Never draw the green tube without first drawing a white discard tube which must as its name implies be thrown away.

 

Order	Cap colour	Monovette tube	Remarks
1		Aerobic blood culture	Bacteriology
2		Anaerobic blood culture	Bacteriology
3	White	Native white blood	Standard chemistry (tests) - Special chemistry (tests) Always use a tube for priming if you are using a butterfly needle.
4	Green	Citrate 1/10	Coagulation
5	Purple	Citrate 1/5	Sedimentation rate
6	Red	EDTA	Haematology – Transfusion – Genetics – Molecular biology
7	Orange	Heparin	Chemistry
8	Yellow	Sodium fluoride	Lactate - Glucose
9	Other	Other tubes	On request for special analyses

 

Urine samples

Urine is used in the laboratory to highlight various pathologies and requires a suitable sample depending on the analyses:

• 1st urine taken midstream for urine sediment, quick tests (urine strips), clinical chemical tests.
• 2nd morning urine for urinary glucose, urinary proteins, urinary strips with the exception of nitrate investigations.
• 24-hour urine collection for quantitative chemical assays.

24-hour urine collection

• 24-hour urine collection starts at 7:00 a.m. after emptying the bladder and discarding the first urine and ends at 7:00 a.m. the following morning with the first urine that must be combined with the total volume of urine collected.
• Add preservative if required for the chemical dosing. Note that for HCI, preservative must only be added to the collection jar after the 2nd urination.

 

Urination flow

• Wash hands thoroughly.
• Spread the vaginal lips or pull back the foreskin.
• Wash external genitalia with a paper towel.
• Urinate the initial urine into the toilet.
• Urinate 50 to 100 ml of urine in the yellow collection container.
• Close the cover properly.

 

Preservatives

HCl (hydrochloric acid) required for the following analyses:

• Calcium
• Citrate
• Homovanillic acid
• 5-Hydroxyindoleacetic acid
• Catecholamines
• Metanephrines
• Oxalate
• Vanillylmandelic acid

 

Plan for the following urinary assay

5-Hydroxyindoleacetic acid: for the 2 days preceding the collection and during the latter, avoid: pineapple, eggplant, avocado, banana, kiwi, melon, tomato, nuts.