Certain factors may affect test results, and in certain cases may make the results somewhat inaccurate. Stress, fasting before a test, or how the test is handled by the laboratory may all have an effect. This section covers some of the more commonly seen issues.

Cornell University College of Veterinary Medicine has more information on these factors. Click on the links on the left for more information.

Fasting a Cat Before Tests

If cats are not fasted before blood draws, then lipaemia may occur, particularly if the cat has eaten a meal rich in fat. This means that lipids (fats) are suspended in the blood, which may make the sample thicker and harder to test.

However, lipaemia is relatively rare in feline blood samples, and even if it is present, it is unlikely to make a major difference to the test results. Therefore it is not usually necessary for a cat to fast before the usual tests for CKD, and overall I think it is a bad idea because an empty stomach can increase the risk of stomach acid; plus when they are being fasted, cats simply do not understand why we won't feed them, which is stressful for them, especially if other family cats continue to get fed whilst they do not. However, for certain specialised tests, such as those for parathyroid hormone or pancreatitis, fasting for twelve hours may be necessary; be guided by your vet.

Stopping Fluids Before Testing

I have heard of some vets asking that people not give their cats fluids for a day or two (in one case, a week!) before bloodwork. I do not understand this: since the cat normally receives fluids, surely you will obtain more accurate results, reflecting how the cat's bloodwork normally looks, if the cat has his/her usual levels of hydration. But I do recommend that you try to be consistent i.e. always have the tests done before sub-Qs or after sub-Qs, at the same time of day if possible.

Stressed Cats or Cats Who Fight Blood Draws

If your cat fights at the vet, or gets very stressed, this may have an effect on some of the test results. For example, blood glucose levels are often raised in stressed cats, so they do not automatically indicate that diabetes is present. Similarly, CK or CPK, a muscle enzyme, may be raised because of a bad blood draw.

Haemolysis

Occasionally bloodtest results will mention that they are haemolysed. This means the blood cells being tested have ruptured, often as a result of poor handling. Mild haemolysis should not have any real effect, but a grossly haemolysed sample may affect results, causing some values (such as phosphorus) to appear higher than they are and others (such as creatinine) to appear lower. Potassium will usually appear higher than it really is, but occasionally it will appear lower. If a sample has been haemolysed, you might wish to ask your vet to take new blood samples and run the tests again.

Cornell University College of Veterinary Medicine has information on the impact of haemolysis.

BD Tech Talk has more information on haemolysed samples.

Antech also provides information on this issue.

Clumping Platelets

Platelets are the component of blood which causes it to clot. If they were not present, we would bleed to death whenever we got cut.

Unfortunately when a sample of blood is taken, some of the platelets may "clump" (stick together), especially if the blood sample is not mixed with the anticoagulant immediately. Clumping platelets are extremely common in cats  - they occur in as many as 75% of cat blood draws. They are even more likely if it is difficult to get blood from the cat. Taking them from a leg rather than from the neck may also be a factor.

The clumping means that it can be difficult to count the platelets accurately, which in turn means that the number may appear low. However, you may sometimes see platelet counts listed as low, followed by a comment that the platelet estimate is "adequate." This means that the person running the test could not tell the platelets apart enough to be able to count them, but could see that overall there are enough.

If a cat truly has low platelets, then you may see increased bleeding e.g. from the nose, gums or in urine.

Cornell University College of Veterinary Medicine has more information on platelets.

Pet Place has some information about low platelets (no need to register to read the article, just click on Close at the bottom of the irritating pop-up).

Differences Between US and International Measurement Systems         Back to Page Index

The USA uses a different measurement system to the rest of the world, which uses the SI system (Système Internationale). Although I am familiar with both systems, having lived in both the UK and the USA, Tanya's Feline CRF Support Group has primarily American members, so you will get more feedback when you join if you post your results in American values.

In order to do this, there is a handy converter on the Veterinary Information Network website. Remember to choose the feline measurements and to enter the SI (international) measurements for conversion to US equivalents, not the other way round. When converting urea from your international results, choose BUN from the dropdown menu - that is the nearest US equivalent. When converting creatinine, be sure to choose creatinine rather than creatine, which is also in the dropdown menu.

Sometimes the conversion site is down, but usually not for long. However, if you can't get it to work, here is a rough guide to the calculations:

Urea (BUN)

• You multiply the international value by 2.8

  • e.g. urea of 50 is a BUN of 140.

   

• If you don't have a calculator, you can do it roughly by simply multiplying by 3.

  • e.g. urea of 50 is about BUN 150.

  • Note: this slightly overstates it.

Creatinine

• You divide the international value by 88.36.

  • e.g if a cat has creatinine of 300, then it is 3.4 in US values.

   

• If you don't have a calculator, you can just do it roughly by dividing by 100 and adding on about 10%.

  • e.g. if a cat has a creatinine of 300, dividing by 100 gives you 3, then add on 10%, which gives you 3.3.

  • Note: this slightly understates it.

Phosphorus

• You multiply the international value by 3.1.

  • e.g. phosphorus of 4 international is 12.4 in US values.

   

• If you don't have a calculator, you can do it roughly by simply multiplying by 3.

  • e.g. phosphorus of 4 is about 12 in US values.

  • Note: this slightly understates it.

Potassium

• This is the same in both systems, so no need to convert anything.

PCV/HCT

• This is the same in both systems.

• However, sometimes in international values, it will be shown differently,e.g. 0.30% rather than 30%.

• If this happens, simply move the decimal place along two places.

Why Ranges Differ Between Laboratories

Lab Tests Online also explains more about this.

Normal Ranges for Blood and Urine Tests

*This site also gives instructions on how to take the measurements

Veterinary Links Explaining Blood Tests                                                       Back to Page Index

To obtain more information on what the different measurements on your cat's bloodwork mean, try some of these websites:

Washington State University - helpful information, and perhaps easier to understand than Cornell.

Columbia Animal Hospital gives a brief summary of the various results you may see on your cat's bloodwork.

Pet Education has some helpful sections:

• complete blood count

• chemistry panel

• dictionary of medical terms

Links on this page last checked: 20 November 2011