How to avoid common sample artefacts and get the most accurate results
We’ve all had to run that strawberry milkshake sample, or pulled that fluorescent yellow sample out of the centrifuge.
Or we’ve been the unlucky nurse called to sample the patient with notoriously difficult veins, and try as we might to get a nice sample, it just ends up haemolysed.
But what do these sample artefacts mean for our patients? And how can we avoid them?
In this post, I’m going to tell you exactly how the most common sample artefacts affect our results. We’ll chat through when these artefacts occur, the parameters they can make inaccurate, and how to adjust your sampling technique to avoid them.
Don’t forget - if you want to learn more about interpreting biochemistry results, so you know exactly what each parameter means and how it affects our patients, join me in 3 weeks for the Biochemistry 101 Workshop!
You can get access via the Medical Nursing Academy when doors open on February 1st - to get more details and be the first to know when it goes live, join the waitlist below!
Let’s talk artefacts
There are four main artefacts we’re going to cover here: haemolysis, lipaemia, icterus and improper handling. Each are seen in different patients and situations, and cause different changes to our results.
We can’t always avoid these artefacts. Some are just part of our patient’s disease process - like icterus, for example. But, by at least being aware of them and the parameters they can affect, we can take this into consideration when interpreting our results.
Haemolysis
Haemolysis is the damage or breakage of cells. These samples have a characteristically red or pink-tinged serum/plasma, depending on the severity of haemolysis present.
It is commonly seen:
If a sample is mixed too vigorously (e.g. shaken) in the tube after collection
If samples are taken into moist syringes
If excessive negative pressure is placed on the blood during collection
If the blood is transferred into a tube through the needle, rather than directly from the syringe
If excessive alcohol is used to prepare the site, and this not fully evaporated prior to venepuncture
We may also see this as part of a patient’s disease process, for example in patients with haemolytic anaemia, or those having a haemolytic transfusion reaction.
What changes do we see in a haemolysed sample?
Haemolysis can cause a variety of changes to our biochemistry and haematology results.
Since many analytes are present in the intracellular fluid and extracellular fluid in different quantities, if haemolysis occurs, the levels of these analytes can be less accurate. Potassium, for example, is present inside the cells in much higher concentrations than it is outside of the cells. If these cells became damaged, the analytes in the intracellular fluid would ‘leak’ into the blood, changing the levels in the sample.
Other parameters can become diluted by the fluid released from the ruptured cells.
Haemolysis also interferes with AST, amylase, CK, glucose, phosphorus, total protein, cholesterol, calcium, fructosamine, sodium, potassium, albumin, lipase and bilirubin levels. So these results may not be accurate in a haemolysed sample, depending on the degree of haemolysis.
How can we prevent this?
To minimise haemolysis:
Use the largest bore needle your patient will comfortably tolerate
Avoid placing excessive negative pressure on your syringe during sampling
Fill sample tubes directly from the syringe, not via the needle
Gently rock tubes to mix the blood and anticoagulant
Lipaemia
Lipaemia is an abnormally high level of lipids in the blood. Samples have a classic ‘strawberry milkshake’ appearance when centrifuged.
We can see lipaemia if a patient has been fed prior to sampling, especially if the meal was high in fat. It can also be seen in patients with various diseases, including:
Pancreatitis
Diabetes mellitus
Hypothyroidism
Hyperlipidaemia
Hypercortisolism/Cushing’s disease
What changes does lipaemia cause?
Lipaemia can cause significant changes to our biochemistry results, including:
Increased calcium levels
Increased phosphate levels
Increased bilirubin levels
Increased glucose levels
Increased total solids levels
Increases in liver parameters such as ALP, ALT and AST
Decreases in albumin levels
Decreases in sodium, potassium and chloride levels
What should I do if my sample is lipaemic?
If your sample is lipaemic, or your patient is at risk of lipaemia, try the following:
Taking fasting samples wherever possible
Delaying the sample for a few hours if non-urgent
Centrifuging the sample at a higher speed to separate the lipid layer from the rest of the sample
Refrigerating the sample to separate the lipid layer from the rest of the sample
Icterus
Icteric serum/plasma is caused by excess levels of bilirubin in the blood. This happens due to 3 different reasons:
Pre-hepatic: increased bilirubin production (from RBC breakdown, e.g. in IMHA patients)
Hepatic: inappropriate excretion of bilirubin in the liver (e.g. due to hepatic disease)
Post-hepatic: inappropriate excretion of bilirubin in the biliary tract (e.g. due to biliary tract obstruction)
To determine what’s causing the icterus in your patient, you need to:
Look at the patient’s clinical history/signs and examination findings
Examine the PCV
Examine the other liver parameters
Examine the rest of the biochemistry results
If anaemia is present, a pre-hepatic cause is likely. However, differentiating between hepatic and post-hepatic icterus is not always easy.
A more severe increase in ALT than ALP may indicate a hepatic icterus, and vice versa.
If changes to the liver function parameters - urea, glucose, cholesterol, albumin and/or bile acids - are present, this points to a hepatic cause.
Lastly, imaging of the liver and gall bladder (e.g. abdominal ultrasound) can be considered. This may reveal abnormalities such as dilation of the biliary tract, biliary stones, or a gall bladder mucocele, indicating a post-hepatic cause.
What changes does icterus cause to our results?
Icterus is not strictly a sample artefact - we’re not causing it - but it is a common cause of serum/plasma discolouration, and a common abnormal finding in medical patients.
The high bilirubin levels themselves can also alter levels of:
Cholesterol
Triglycerides
Lipase
Total protein
GGT
So this is something we need to consider in our icteric patients.
Improper Handling
It is vital for veterinary nurses to handle and store laboratory samples correctly. Improper handling and storage can cause various artefacts, such as alterations in enzyme/assay levels, or changes to the blood cells themselves.
For example, RBCs consume glucose in vitro, causing falsely low glucose results.
To minimise these changes, samples should be analysed as soon as possible after collection - ideally within an hour (some tests, such as ammonia, need to be run sooner than this).
If samples become too warm, thermal damage may destroy some analytes, and activate others - such as enzymes.
So that’s an overview of the common sample artefacts we see, and how they affect our results! To sum up, common artefacts include haemolysis, lipaemia and icterus. These cause a variety of changes to our biochemical parameters.
To minimise the effect of haemolysis, avoid negative pressure, select an appropriately-sized needle, and mix samples gently.
Lipaemic samples can be avoided by taking samples on an empty stomach, or potentially by centrifuging samples on a higher speed, or by refrigerating them to separate the lipid layer.
The way we handle samples also has an effect on our results. Samples should be analysed as soon as possible after collection, and excessive heat avoided.
Did you find this helpful? Will it change your considerations when collecting blood from your patients? DM me on Instagram and let me know!
And don’t forget - if you want to know more about the common biochemistry results we see and what they mean, join me for the Biochemistry 101 workshop!
References
Cornell University. 2020. Interference Indices [Online] EClinPath. Available from: https://eclinpath.com/chemistry/interference-indices/
Papajeski, B. 2021. How to collect and prepare samples for the laboratory [Online] Today’s Veterinary Nurse. Available from: https://todaysveterinarynurse.com/clinical-pathology/how-to-collect-and-prepare-samples-for-the-laboratory/
Poli, G. 2022. Lipaemia - the bane of biochemistry [Online] Vet Times. Available from: https://www.vettimes.co.uk/lipaemia-the-bane-of-biochemistry/
Poli, G. 2022. PCV/total solids interpretation: serum colour [Online] Vet Times. Available from: https://www.vettimes.co.uk/pcvtotal-solids-interpretation-serum-colour/
Poli, G. 2022. Icteric serum [Online] Vet Times. Available from: https://www.vettimes.co.uk/icteric-serum/
Sirois, M. 2020. Laboratory Procedures for Veterinary Technicians. 7th ed. Missouri: Elsevier.
