Preanalytics: Blood, plasma, serum samples

Details on the recommended material (blood, serum, plasma) for the requested test can be taken from our test descriptions or the submission form. For labelling the sample, it is also necessary to indicate the sample type.

 

Whole blood samples

EDTA blood (EB)

– For doing a blood count, EDTA blood is the most suitable material in mammals (however,for birds and reptiles it is heparin blood, see below).
– For the serological examination of the blood type, EDTA whole blood is needed as well.
– As the cells in the sample are not stable, EDTA samples for haematological tests should not be older than 48 hours.
– For most PCR analyses and genetic tests, EDTA blood is required.
– To determine certain parameters such as ACTH or pro-BNP, only EDTA plasma which was promptly centrifuged and cooled can be used to obtain reliable results.

Heparin blood (HB)

– To collect heparin samples, lithium heparin (LiHep) tubes are available.
– For doing a blood count in reptiles and birds, lithium heparin blood should generally be used.
– Since the amount of blood is often very low in small mammals, lithium heparin tubes are particularly suitable, as they cannot only be used for doing a blood count but also
for determining a wide range of blood-chemical parameters.
– For the PCR, lithium heparin whole blood should only be used under exceptional circumstances, as lithium heparin can inhibit the PCR and might thus lead to false negative results.

Citrate blood (CB)

– To determine the coagulation parameters, only the appropriate citrate tubes should be used. For getting a correct evaluation, their shelf life may not be exceeded. It is also necessary to have an exact mix ratio of 1:10 (1 part citrate + 9 parts blood).
– For correctly performing platelet function tests, citrate whole blood is required.

Sodium fluoride blood (NaFB)

Sodium fluoride inhibits enzyme activities which lead to a reduction of some parameters. It should be used for the correct determination of glucose and lactate.

 

Plasma

– Samples are drawn into tubes with anticoagulants (heparin, EDTA, citrate).
– Can be centrifuged immediately after collection (10 min, 2000 g).
– Remove the supernatant by pipette and transfer it into an uncoated test tube, then indicate the sample materials on the test tube or use the appropriate bar code label (see Labelling).
– Please note: The additives limit the number of analyses!
– Heparin plasma (HP) is needed for many clinical-chemical examinations. HP cannot be used for agglutination tests.
– The collection of EDTA plasma (EP) for clinical-chemical and/or serological parameters should only take place in exceptional cases, as EDTA disturbs through various mechanisms the measurement of individual parameters such as calcium, magnesium and AP. Likewise, potassium cannot be determined when using EDTA plasma, since EDTA is added as K-EDTA.
– Some coagulation parameters can only be analysed using citrate plasma (CP). Performing platelet function tests using centrifuged citrate plasma is not possible.

 

Serum

– Samples are drawn into tubes without anticoagulants.
– Allow to stand for 30 – 60 min.
– Centrifuge for 10 min at 2000 g.
– Remove the supernatant by pipette and transfer it into an uncoated test tube, then label the test tube.
– For the correct determination of individual parameters, only serum should be used (see detailed descriptions provided for the individual parameters).
– Sending non-centrifuged samples should only be done exceptionally (e.g. in case of a very low sample quantity), as the transport might result in cell damage and thus lead to haemolytic serum.

 

An overview of the different tubes can be found in here.

Haemolysis

Haemolysis is caused by leakage of intracellular components of the erythrocytes such as phosphate, iron, potassium and especially haemoglobin due to a damage of the cell membrane. Haemoglobin causes a red colouration of serum/plasma which primarily interferes with the photometric testing done in clinical chemistry.

Lipaemia

Haemolysis is caused by leakage of intracellular components of the erythrocytes such as phosphate, iron, potassium and especially haemoglobin due to a damage of the cell membrane. Haemoglobin causes a red colouration of serum/plasma which primarily interferes with the photometric testing done in clinical chemistry.

Icterus

Icterus is a yellowish discolouration of serum/plasma. Excess amounts of bilirubin, which is the reason for the yellow colouring, are normally caused by a medical condition
and cannot be influenced. Very severe icterus may sporadically affect certain parameters.
The yellow colouration is physiological in horses.

 

Interfering factor	Parameter	Level
Haemolysis	LDH, HBDH, CK, AST, bilirubin, creatinine, PO4, K, Mg, Fe, fructosamine	elevated
Haemolysis	Ca, glucose	lowered
Lipaemia	ALT, AST, GLDH, γ-GT, AP, bilirubin, creatinine, haemoglobin	elevated
Lipaemia	amylase, Na, CI, K	lowered

 

Medicine	Parameter	Level
Penicillin G	K	elevated
Tetracyclines	PO4	elevated
Tetracyclines	K	lowered
Salicylates	CK, AP, glucose, Na, total protein	elevated
Salicylates	K, Ca	lowered
Corticosteroids	CK, AP, glucose, Na, total protein	elevated
Corticosteroids	K, Ca	lowered
Phenylbutazone	Ca, Na	elevated
Barbiturates	CK	elevated
Halothane anaesthesia	CK, PO4	elevated
Glucose infusion	glucose	elevated
Glucose infusion	PO4	lowered

Blood counts

– Pay attention to the fill volume! Preferably fill up to the mark, since an insufficient volume can result in changes in cell morphology. Do not overfill the tube in any case, as the sample might clot.
– After drawing the sample, tilt the test tube carefully several times. Do not shake it.
– Do not store blood smears in the refrigerator and not close to formalin.
– Pack the samples frost-proof in winter; possibly cool them in summer.
– Reliable results can only be obtained from samples not older than 48 hours.

Clinical chemistry of serum or heparin plasma

Prompt centrifugation of the samples will lead to better test results, as it reduces the risk of haemolysis caused by transportation. However, serum should be allowed to stand for a minimum of 30 min to ensure a complete clotting of the sample.
Serum samples can also be shipped frozen; they will then reach the laboratory cooled. Repeated freezing/thawing, though, should absolutely be avoided.

Determination of glucose and lactate

– Requires sodium fluoride blood or sodium oxalate blood or serum which was promptly centrifuged.
– Fill volume: Fill the sample tubes exactly up to the mark. If the quantity is too small or too large, results may be incorrect.

Coagulation parameters

– Determination is carried out using sodium citrate plasma which is obtained from citrate blood with the mix ratio being 10:1 (9 parts blood + 1 part sodium citrate). Centrifugation should take place at the practice. When testing for the von Willebrand antigen, it is imperative to do this promptly after collection.
– If commercial citrate-treated tubes are used, the expiry date needs to be checked before collecting the sample. Expired tubes may no longer be used, as skewed results are to be expected. When drawing the sample, special attention must be paid to the exact fill level (marking on the tube).
– If no commercial tubes are available, sodium citrate 3.13% can be drawn into a syringe.
– No heparinised needles or catheters may be used.

Sample collection for bone marrow cytology

– Sample material from the first aspirate should be used to prepare the smears fo cytological examination (avoid contamination with peripheral blood).
– The syringe used for aspiration should be preloaded with an anticoagulant. The aspirate should be placed into an EDTA, lithium heparin or citrate tube at the latest immediately after the puncture and then inverted well to avoid clots.
– To prepare a smear, the aspirate is put in a Petri dish and gently inverted in order to find the bone marrow spicules.
– The spicules are each placed on a slide and carefully spread to form a monolayer.
– The remaining aspirate is then put back into the tube (wetted with the same anticoagulant) and sent in as well.
– In addition, peripheral blood is collected in a tube, a blood smear is prepared and both are also sent to the laboratory.