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Tag: Cushing’s Disease

  • Lipaemia – the bane of biochemistry

    Lipaemia – the bane of biochemistry

    Last week we covered haemolysed samples – this week we’re looking at lipaemic samples.

    Lipaemic samples are caused by an excess of lipoproteins in the blood, creating a milky/turbid appearance that interferes with multiple biochemical tests and can even cause haemolysis of red blood cells.

    lipaemic sample
    A severely lipaemic sample (red arrow). IMAGE: eClinPath.com (CC BY-NC-SA 4.0).

    Lipaemia can follow recent ingestion of a meal – especially one high in fat. Although not pathognomonic for any diseases, its presence can help increase the suspicion of certain diseases, including:

    • pancreatitis
    • diabetes mellitus
    • hypothyroidism
    • hyperadrenocorticism
    • primary hyperlipidaemia (in some specific breeds, such as the miniature schnauzer)

    It warrants further investigation in patients that have been ill and inappetent.

    Irksome interpretations

    Lipaemia can dramatically impact laboratory testing and is often troublesome in critically ill patients, making interpretation of biochemistry particularly difficult, if not impossible.

    Lipaemia can affect different analysers in different ways, most commonly causing:

    • Falsely increased calcium, phosphorus, bilirubin, glucose and total protein (via refractometer) and some liver parameters such as alkaline phosphatase, alanine aminotransferase, aspartate aminotransferase, haemoglobin concentration, and mean corpuscular haemoglobin concentration.
    • Falsely decreased sodium, potassium, chloride, albumin and bicarbonate.

    Tube tips

    Assessment of a centrifuged haematocrit tube before running a biochemistry panel can help reduce wasted biochemistry consumables.

    If the sample is lipaemic in the haematocrit tube then maybe try some of the following tips.

    • If blood tests are planned in advance, try fasting the patient beforehand for 12 to 24 hours.
    • Repeat sampling a couple of hours later may yield a less lipaemic sample.
    • Collecting and centrifuging a larger amount of blood (3ml to 5ml, for example) can sometimes yield enough clear sample between the lipid layer and red blood cells.
    • Refrigeration of the sample can help the separation.
    • Extract lipids using polar solvents, such as polyethylene glycol.
    • Centrifugation at higher than normal speeds (if possible) can also assist in clearing the layer.
  • Fluid therapy part 4: ongoing losses

    Fluid therapy part 4: ongoing losses

    This month, we will look at the final part of a fluid therapy plan – accounting for ongoing losses. This can be challenging, but some general rules can be helpful.

    Regular assessment is essential to track patients' response.
    Regular assessment is essential to track patients’ responses.

    First, let’s recap the four parts of a fluid therapy plan:

    1. Perfusion deficit
    2. Hydration deficit
    3. Maintenance requirements
    4. Ongoing losses

    When considering ongoing losses, try to not forget about patients with pre-existing polyuric diseases; chronic renal failure is a prime example. Patients with dehydrated chronic renal failure are unlikely to suddenly regain concentrating ability. Polyuria should be considered as an ongoing loss.

    Other conditions that may result in additional urinary fluid losses include post-obstructive diuresis, diabetes mellitus, hyperadrenocorticism and hyperthyroidsim.

    How much to add?

    This is the tricky part. I often add an additional half to one maintenance and frequently reassess clinical parameters, or if a urinary catheter is placed matching ins and outs.

    Gastrointestinal tract losses can be collected and weighed; 1g of vomitus or diarrhoea can be roughly equivalent to 1ml of water.

    Fluid removed from drains placed in cavities or wounds should also be measured and accounted for.

    Remember the key point is regular assessment of the patient’s hydration status, from repeat clinical exams, to track their response. Don’t forget regular retesting of electrolytes – for example, every 12 to 24 hours for patients on IV fluids and not eating.

  • SNAP cortisol test

    SNAP cortisol test

    While hyperadrenocorticism is not an uncommon incidental finding in patients presenting to our emergency clinic, hypoadrenocorticism is a lot less common. Or, possibly, more frequently underdiagnosed.

    Textbook clinical presentations combined with haematology and biochemicial changes can make diagnosis straightforward, but not all patients will present with all the classic signs.

    SNAP cortisol test
    The SNAP cortisol test is a quantitative ELISA test that measures the level of serum cortisol in dogs.

    To complicate things further, hypoadrenocorticism is the great mimicker of diseases; it is often impossible to arrive at a definitive diagnosis without knowing the cortisol levels.

    The SNAP cortisol test allows clinicians to determine cortisol levels in-house – a blessing to those of us who work out-of-hours – but is not without its limitations.

    Suspicious signs

    Patients with hypoadrenocorticism often present with vague and non-specific clinical signs, but certain clinicopathological changes help raise the suspicion:

    • a decrease in sodium-to-potassium ratio (below 1:27)
    • azotaemia
    • an inappropriately low urinary specific gravity, despite evidence of dehydration or hypovolaemia
    • a leukogram unfitting to the degree of illness of the patient (a “reverse stress leukogram”- neutropenia, lymphocytosis, eosinophilia)
    • anaemia
    • hypoglycaemia
    • hypercalcaemia

    Although most Addisonian patients will not present with all these signs – especially those in the early stages of disease or those with atypical Addisonian disease (glucocorticoid insufficiency only) – any patients showing any of these haematology and biochemicial changes should have hypoadrenocorticism ruled out as part of the diagnostic plan.

    Imperfect ELISA

    The SNAP cortisol test has been advertised as an in-house assay to aid the diagnosis, treatment and management of both hyperadrenocorticism and hypoadrenocorticism, although the quality of the result is not perfect. This quantitative ELISA test measures the level of serum cortisol in dogs.

    In one study1, the SNAP cortisol test appears to have a good correlation with an external laboratory chemiluminescent assay test; however, in 12.8% of cases (5 of 39 patients), the SNAP test result could have led to a different clinical decision regarding the management of the patient.

    Since long-term Cushing’s management relies on reliable, repeatable cortisol level detection, this high level of discrepancy is unacceptable, especially when more accurate alternatives are available at external laboratories.

    Still useful

    Despite this, it is still very useful helping to assess for the presence or absence of hypoadrenocorticism, especially in an emergency setting.

    I use the SNAP cortisol to measure the resting cortisol level. If it is below 2ug/dL or in inconclusive range (between 2ug/L and 6ug/L), but the clinical picture suggests hypoadrenocorticism, I would perform an adrenocorticotropic hormone (ACTH) stimulation test and send samples to an external laboratory. If it is well above the inconclusive range, I would not perform an ACTH stimulation test.

    In summary, I think the SNAP cortisol test can be useful in helping assess for hypoadrenocorticism, but would still recommend performing an ACTH stimulation test and running the samples externally.

    However, use it with caution for hyperadrenocorticism diagnosis and its long-term management – especially when more accurate and economical alternatives are available.

  • Barking up the right tree – with Trusty Paws

    Barking up the right tree – with Trusty Paws

    Originally a charity set up by veterinary students for the homeless hounds of Glasgow in October 2014, Trusty Paws has become incredibly successful and has received a huge amount of public support.

    The Trusty Paws Clinic logo

    This success has allowed the charity to run monthly clinics at the Simon Community Scotland drop-in centre, providing free health checks, vaccinations, microchipping, and flea and worming treatment for the pets of the homeless.

    Essential supplies, such as food, coats and harnesses for the dogs, are also given out at these clinics for those in need.

    Branching out

    The success of the Glasgow clinics has led to a branch of the charity opening in London, with the first clinic taking place in November 2015.

    Run by fourth year RVC students, the clinics take place at the West London Day Centre in Marylebone, which also provides other services for the homeless.

    The expansion of the charity is excellent news for the pets of the homeless, for whom we can continue to provide the veterinary care they deserve.

    In at the deep end

    The Glasgow clinics are organised by the student committee, but health checks are conducted by other fourth year student volunteers. Last week I had the chance to get involved and, under the supervision of a volunteer vet, conducted my first full consultation that didn’t involve actors in a communication skills class.

    My patient, Bruno, wasn’t particularly well. The owner said he was not himself (he certainly looked depressed), had lost a significant amount of weight since his last visit and had a slow heart rate, in addition to some evident skin issues.

    The vet suspected Cushing’s disease, so we referred him to the local Pets’n’Vets branch that undertakes any secondary veterinary care Trusty Paws patients require. They have conducted blood tests, paid for by the charity, and have confirmed the diagnosis.

    Offering support

    While a little daunting to be thrown straight into a full consultation, I thoroughly enjoyed helping out at the clinic and would certainly encourage other students (whether in Glasgow or London) to do so in the future.

    The clients are extremely appreciative and evidently love their pets dearly, so it’s easy to see the benefits of such a charity to everyone involved.

    • If you can’t get directly involved, but wish to offer financial support, donations can be made via PayPal.
    • Alternatively, the charity has two Amazon wishlists (one for Glasgow, one for London), enabling supporters to purchase specific products that each clinic requires.