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Factors That May Affect Test Results

Converting International Values to US Values

Normal Ranges

Veterinary Links About Test Results



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Home > Diagnosis > Test Ranges, and Factors Which May Affect Results



  • There are a number of factors which may affect test results. This page discusses these factors, such as whether it is necessary to fast a cat before blood tests.

  • This page gives a rough idea of normal ranges for tests commonly run on CKD cats, and explains why there are differences between various laboratories. It also has veterinary links explaining more about test results.

  • Ranges for test results differ between the USA and the rest of the world. This page explains those differences.

Factors That May Affect Test Results


Certain factors may affect test results, which in some cases may make the results somewhat inaccurate.


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


Advanced diagnostics: impact of interferants (2007) Rebar AH & Christian JA NAVC Clinician’s Brief Nov 2007 pp29-31 explains more about the things that may affect test results.

Fasting Before Testing

Lipaemia may occur in non-fasted blood samples, 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 gastric hyperacidity. Also, cats who are being fasted 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.


For certain specialised tests, such as those for parathyroid hormone or pancreatitis, fasting for twelve hours may indeed be necessary; be guided by your vet.


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


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.


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.



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 to appear higher than they are and others to appear lower:

  • phosphorus can appear higher than it is

  • creatinine may appear lower than it is

  • 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.


What is hemolysis? (2003) Arzoumanian L Becton Dickinson Tech Talk 2(2) pp1-2 has more information on haemolysed samples.


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 were 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.


Differences Between US and International Measurement Systems


Everywhere in the world uses the SI system (Systčme Internationale D'Unités) as its measurement system, apart from the USA.


Although I am familiar with both systems, having lived in both the UK and the USA, Tanya's Feline CKD Support Group has primarily American members, so you will get more feedback when you join if you post your results in American values.


Units Used



Commonly used units in the international system are:



millimole per litre.

The SI unit in medicine for measuring concentrations of substances in the blood.



micromole per litre. This is 1000 times smaller than mmol/L. So for example 1 mmol/L is the same as 1000 µmol/L.

Since not everybody can access the µ symbol, sometimes you will see umol/L instead.

This measurement is used for creatinine and some other values.



This is grams per liter.

It is not part of the SI but is often used for some reason for urea in France and Portugal.



Commonly used units in the US system (which are also sometimes used in some European countries) are:



milligram per deciliter, the unit used in medicine to measure the concentration of substances in the blood.

1 mg/dl equals 0.01 grams per liter (g/L ).



Milliequivalents per liter.

This is normally used for potassium.

In practice, the values are exactly the same as those expressed in mmol/L.


Converting Urea into BUN (Especially from French Measurements)

The USA usually measures blood urea nitrogen or BUN. Most other countries measure urea. When converting urea from your international results, choose BUN or blood urea nitrogen from the dropdown menu — that is the nearest US equivalent. 


Normally if you are converting from international to US values, you are converting from mmol/l to mg/dl. However, in France and Portugal the measurements are often in g/l but as is usual in Europe, they are for urea, rather than BUN. You have to do some quite convoluted calculations to obtain the US BUN equivalent. BUN/urea (2016) Abbott Laboratories Abbott Point of Care says: "To convert a BUN result in mg/dL to a urea result in mmol/L, multiply the BUN result by 0.357. To convert a urea result in mmol/L to a urea result in mg/dL, multiply the mmol/L result by 6. To convert a urea result in mg/dL to a urea result in g/L, divide the mg/dL result by 100."


You actually want to do things the other way around. Here is the formula (but below are converters that will do it for you automatically):

  • Take your urea value in g/l

  • Multiply by 100 to get the mg/dl result for urea

  • Then divide by 6 to get the mmol/L value for urea

  • Then divide by 0.357 or multiply by 2.8 to get BUN in mg/dl

I did this with Thomas's extremely high 86 mmol/l urea level (BUN of 241) to check:


Urea value  5.16 g/l

5.16 g/l urea

Multiply by 100

516 mg/dl urea

Divide by 6

86 mmol/L urea

Divide by 0.357 or multiply by 2.8 to get BUN

241 mg/dl BUN


Alternatively, you can replace the last two steps by simply dividing the urea mg/dl (516 in this case) by 2.1428 to obtain the same result (241 in this case). This also applies if you are given urea in mg/dl and wish to convert it to BUN in mg/dl.


Rapid Critical Care Consult will do the calculation for you, which is a lot easier. Click on urea, then click on the dropdown menu next to it that says mg/dl and choose g/l if you are in France or Portugal and have your results in g/l. Choose urea and mmol/l if you are in the UK or other countries using mmol/l. Choose urea and mg/dl if you are in Germany or other German speaking countries which list urea in mg/dl.


Conversion Websites

The Nephron Information Center has an excellent converter so you can convert your measurements as necessary. Remember to click on the SI/L button, and to convert urea to BUN.


Jay Clinical Services also has a calculator.


Manual Conversion

Here is a rough guide to the calculations. This is a very rough guide, and all values are approximate.


Urea (BUN)

If you have a urea measurement in mmol/L, you multiply the international value by 2.8 (or divide by 0.357):

  • e.g. urea of 50 mmol/L is BUN of 140 mg/dl.

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

  • e.g. urea of 50 mmol/Lis about BUN 150 mg/dl. Note this slightly overstates it.


If you have a urea measurement in mg/dl (often the case in Germany, Austria and Italy), you multiply the international value by 2.14:

  • e.g. urea of 65 mg/dl is a BUN of 140 mg/dl

If you don't have a calculator, you can do it roughly by simply multiplying by 2:

  • e.g. urea of 65 mg/dl is about BUN 130 mg/dl. Note this slightly understates it.


If you have a creatinine measurement in µmol/L, you divide the international value by 88.36:

  • e.g if a cat has creatinine of 300 µmol/L, then it is 3.4 mg/dl.

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 µmol/L, dividing by 100 gives you 3, then add on 10%, which gives you 3.3. Note this slightly understates it.


If you have a phosphorus measurement in mmol/L, you multiply the international value by 3.1:

  • e.g. phosphorus of 4 mmol/L is 12.4 mg/dl.

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

  • e.g. phosphorus of 4 mmol/L is about 12 mg/dl. Note this slightly understates it.


Although the units of measurement are different, the values are exactly the same in both systems, so no need to convert anything.



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.


Normal Ranges for Cats


Why Reference Ranges Differ Between Laboratories

You cannot compare tests performed by different laboratories or even those performed on different machines. So if, for example, your vet does tests in-house but also sends them out to an external laboratory, you will probably find the results differ. The quality of veterinary in-clinic and reference laboratory biochemical testing (2012) Rishniw M, Pion PD & Maher T Veterinary Clinical Pathology 41(1) pp92-109 states "caution is needed when comparing results obtained by different methods in the in-clinic and reference laboratory, and knowledge of the methods used for analysis is imperative."


Reference ranges also differ from laboratory to laboratory. Reference ranges are not uniform because of the way they are created. They are created by each laboratory by taking samples from animals who are known to be healthy. They then use these to create a range that in theory represents about 95% of healthy animals. Each laboratory does this differently.


Bias in feline plasma biochemistry results between three in-house analysers and a commerical laboratory analyser: results should not be directly compared (2015) Baral RM. Dhand NK, Morton JM, Krockenberger MB & Govendir M Journal of Feline Medicine and Surgery 17(8) pp653-666 found that in-house analysers are not directly comparable with other analysers, whether in-house or from an external laboratory. It also says that universal ranges (such as those provided by IRIS) may not be appropriate.


IDEXX is one of the big reference laboratories and your vet may send blood out to them for testing. However, if you see IDEXX ProCyte (or Catalyst DX or VetTest) on your cat's results, this normally indicates that your vet is using in-house testing equipment. The machines are calibrated for that laboratory's reference range but there may be some differences.


Generally speaking, reference laboratories are more accurate. This may be in part because they recalibrate their equipment more frequently (though some machines recalibrate automatically these days) and their staff are more skilled at reading results. In-house versus reference lab testing part II (2011) Antech Diagnostics Antech Insights Sep 2011 pp1-7 found that most blood chemistry results from in-house tests were accurate, but there could be problems with the CBC (checks for anaemia or infection).


Personally I view the ability to do tests in-house as a blessing. I remember one horrible long holiday weekend years ago when we had to wait three days for test results from a laboratory to be done, and in the meantime we could not offer our cat anything other than supportive care in hospital. My own feeling is that I like to know what I am dealing with as quickly as possible, so we can get started with a treatment plan. I do not worry too much about results if they are being done in the same way (e.g. always run on the same machine at the vet's) but if you are concerned, you can either always send out your cat's tests to a lab, or do so if they do seem out of sync in some way.


Cornell University College of Veterinary Medicine provides some information on how it creates its reference ranges and why they  differ from laboratory to laboratory.


Lab Tests Online also explain more about this.


Normal Ranges for Blood and Urine Tests: Indicative Only

These ranges are approximate - if those your vet provides are different, which is quite likely, you should be guided by them. I am providing them here just to give you a very rough idea.


These ranges are also not directly comparable. For example, the upper limit for urea/BUN is noticeably lower in the SI system.


Evaluating aging in cats: how to determine what is healthy and what is disease (2016) Bellows J, Center S, Daristotle L, Estrada AH, Flickinger EA, Horwitz DF, Lascelles BDX, Lepine A, Perea S, Scherk M and Shoveller AK Journal of Feline Medicine and Surgery 18 pp551–570 says that "age-related physiologic changes can result in alterations in laboratory values that may be within population intervals." The paper adds that "results obtained from commercial laboratories should be interpreted with caution if reference intervals have not been developed by those laboratories for different age groups." Different ranges are provided for different age groups, should you have full access to the paper.


Therefore this table contains indicative ranges, but that does not necessarily mean that a result within these ranges is acceptable. For example, a CKD cat should aim for a phosphorus level no higher than 4 mg/dl(US) or 1.3 mmol/l (international), while most CKD cats do better if their potassium level is around 4.4 mEq/L or 4.4 mmol/L



Normal Range (International)

Normal Range (USA)

Urea (BUN)

3.5 - 8.0 mmol/L

9.8 - 35.0 mg/dl


40 - 180 µmol/L

0.5 - 1.80 mg/dl

BUN:creatinine ratio

4 - 35

4 - 35


0 - 14 µg/dl

0 - 14 µg/dl


3.5 - 5.5  mmol/L

3.5 - 5.5 mEq/l


0.81 - 1.61  mmol/L

2.5 - 7.50 mg/dl


2.0 - 2.8  mmol/L

 8.0 - 11.2 mg/dl

Ionised calcium

1.0 - 1.4 mmol/L

4.0 - 5.6 mg/dl


0.4 - 2.5 pmol/L

0.4 - 2.5 pg/mL

Phosphorus x Calcium

less than 5

less than 70


141 - 155  mmol/L

141 - 155 mEq/l


17 - 23 mmol/L

17 - 23 mEq/l

Anion Gap

10 - 27

10 - 27

Packed Cell Volume

29 - 45%

29 - 45 %


5.5 - 9.9 

5.5 - 9.9


0.1 - 1.0

0.1 - 1.0

White Blood Cells

5000 - 18000

6 - 19

Neutrophils (segs)

2500 - 12000

60 - 80

Neutrophils (bands)

100 - 300

0 - 3


0 - 1500

0 - 5


1500 - 7000

17 - 32


0 - 850

0 -5


88 - 300

88 - 300 U/L


1.9 - 4.2 mmol/L 

65 - 200 mg/dl


3.85 - 8.25 mmol/L

70- 150 mg/dl


100-1500 /µl

100-1500 U/L


10-130 /µl

10-130 U/L


25 - 40 g/L

2.5 - 4.0 g/dL


23 - 53 g/L

2.3 - 5.3 g/dL

Total protein

5.5 - 8.1 g/dl

5.5 - 8.1 g/dL

Blood pressure

Max: 145 (systolic)

Max: 145 (systolic)


1.008 - 1.060

1.008 - 1.060


270 - 320



38-39 C

101 - 102.5 F


Normal Temperature



38-39 C

101 - 102.5 F


Merck Veterinary Manual gives the ranges as 38.1-39.2 °C or 100.5 to 102.5 °F.


Reference interval for rectal temperature in healthy confined adult cats (2015) Levy JK, Nutt KR & Tucker SJ Journal of Feline Medicine and Surgery 17 pp950-952 found that for the cats in the study, the normal range was much wider, at 98.1-102.1 F or 36.7-38.9 C. The study mentions that geriatric cats may have a different reference range so more research is needed.


Pet Place explains how to take your cat's temperature.


Normal Heart and Respiration Rates

Surprisingly, there appears to be little agreement on what is normal in terms of pulse and respiration, as the table below shows.


Feline cardiology (2011) Côté E, MacDonald KA, Meurs KM & Sleeper MM Wiley-Blackwell gives reference ranges for heart and respiration rates for cats and kittens both at home and at the vet's.


Some people whose cats have heart problems learn how to use a pediatric stethoscope on their cats. Even if you don't do this, ask your vet for guidance on what is normal for your cat.


If your cat appears to be having trouble breathing, i.e. an increase in breating effort or breathing rate, particularly if s/he breathes with the mouth open, it is a medical emergency and you should seek veterinary help immediately.


Respirations are normally measured when the cat is asleep or at least resting. They will always be more frequent when the cat is awake. Breathing in and out once counts as one breath.



Pulse (beats per minute)

Respirations per minute

Merck Veterinary Manual

120 - 140

16 - 40

The Cornell Book of Cats

160 - 240

20 - 30

The Pill Book Guide to Medication for Your Dog and Cat

160 - 180

20 - 40

Pet Place

160 - 220

20 - 30

University of Michigan

130 - 160

20 - 30

Veterinary Drug Handbook

100 - 120 (old cats)



Veterinary Links Explaining Blood Tests


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


Cornell University College of Veterinary Medicine has excellent detailed information on blood tests and urinalysis.

Washington State University College of Veterinary Medicine - helpful information, and perhaps easier to understand than Cornell.


Animal Hospital of Rowlett discusses the tests usually contained in a geriatric panel.


Pet Place also has helpful information:

Small Animal Clinical Diagnosis by Laboratory Methods (5th Ed) (2012) Willard MD & Tvedten H Saunders is a book which explains laboratory tests.



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This page last updated: 13 September 2020

Links on this page last checked: 22 June 2020







I have tried very hard to ensure that the information provided in this website is accurate, but I am NOT a vet, just an ordinary person who has lived through CKD with three cats. This website is for educational purposes only, and is not intended to be used to diagnose or treat any cat. Before trying any of the treatments described herein, you MUST consult a qualified veterinarian and obtain professional advice on the correct regimen for your cat and his or her particular requirements; and you should only use any treatments described here with the full knowledge and approval of your vet. No responsibility can be accepted.


If your cat appears to be in pain or distress, do not waste time on the internet, contact your vet immediately.



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