Meg Sleeper, DVM, DACVIM (cardiology expert!) gave this presentation on how to interpret the information you can get from blood analysis.
Lovingly nicknamed Camilia, PNER’s Abaxis blood machine travels to endurance rides throughout the region. Riders can pay to get their horse’s blood drawn for analysis – this is helpful information for those curious! Beware... it's about to get technical!
Overview (what are these terms and what are we looking for?):
- PCV/TP, CBC (complete blood count – looking at #s of white blood cells), chemistry (this is important and usually taken at rides)
- Packed cell volume (PCV) – manual count (vs. Hematocrit which is done in a machine). Normal results vary by “breed” and “fitness”. Endurance horses tend to have a lower PCV. Red blood cells are important! They are the main oxygen carrying capacity in your blood. They also remove CO2. Anemia results from: blood loss (external or internal – which can be from something like a bleeding ulcer). If anemia is acute, it will take 12-24 hours until PCV accurately reflect that lost because it takes time for the body to compensate. If it’s chronic, however, it should show in the PCV.
Polycythemia means increased red cell count. This is usually seen in dehydration cases (and is usually coupled with high protein levels). Also, if a stressed horse or working horse their spleen will contract and release more red blood cells. The equine spleen has muscles in it that contract with cantering or excitement and dump those cells into the blood stream. An “absolute” change is when you have more RBC than you should (usually because of disease, such as chronic hypoxia, some forms of kidney or liver disease can also cause an increase).
Total protein (TP) in the blood is made up of 3 components: albumin, globulin & fibrinogen. This can be helpful measurement if you are looking at a low PCV horse because it will help you to determine what each means.
- Albumin is a protein produced in the liver and helps prevent fluid from leaking out of the blood vessels. If you have a high albumin, it is consistent with dehydration. If it’s lower than normal, the common reason for that is diarrhea. Kidney disease, liver disease, and other reasons (all chronic disease) can also make this number low.
- Globulins are produced in the liver and are important for immune function. Higher than normal globulins are a sign of inflammation (infection, cancer, etc.). When they are low there are other issues and those are not usually seen in endurance horses (often seen in foals when they haven’t received colostrum).
- Fibrinogen produced by the liver in response to inflammation. A high number indicates active inflammation!
The main two we are interested in is dehydration and the spleen contraction (because the spleen’s contraction will indicate if the horse is truly dehydrated).
Glutamyltransferase (GGT) – can show evidence of liver disease. Donkeys and mules normally have higher levels of GGT than horses. This number can also be elevated in horses in intense training programs.
Aspartate Aminotransferase (AST/SGOT) – the main reason we see this in endurance horses is when there is muscle damage. It peaks 48 hours after muscle damage and takes 3-4 days after the injury.
Creatine Kinase (CK) – Is another muscle enzyme that is not elevated with liver disease. This level is more associated with skeletal muscle or cardiac muscle damage. It can have mild increase with transport, rolling, and hard work. Significant increases to CK (up over 5000) consistent with muscle cell damage. The CK will go up very quickly after damage (peaks within hours of the insult to the muscles) while the AST will peak later and stick around much longer. A CK of 2-3000 after a hard vigorous work is not necessarily tying up!
Creatinine – is a byproduct of muscle work and it’s excreted through the kidneys. It can indicate kidney damage and is a good test for accessing kidney function. Horses that tie up or have another muscle-stressed events are at risk for kidney disease.
Blood urea nitrogen (BUN) – the urea is the byproduct (and is also filtered through kidneys). BUN is increased by GI bleeding. Is the other main test to look at kidney function.
Glucose – Measures the amount of sugar sitting in the blood. Hypoglycemia (the lack of sugar) can happen just because the blood sample sat before it was run – hours can make a difference. Hypoglycemia is also found in cases with endotoxic shock, or young horses that are not eating well. Elevated levels in the blood can be due to excitement, equine metabolic syndrome (pre-diabetes in horses), PPID, etc.
Sodium – Low sodium is most common from loss of sodium in sweat. Equine sweat has a high amount of sodium – more so than their blood level. You can see low sodium because of diarrhea, etc. Increased sodium is often due to water deprivation – something rare in the horses we will be dealing with because we will always be offering them water! Salt poisoning can also occur for horse that eat too much salt. The horse kidney is very good at getting rid of excess electrolytes, at most it will show in an upset stomach (i.e. you might not see it on the blood work).
Potassium – Is indication of the free-P in the blood. However, the majority of potassium is located in the cells. Potassium measure meant because low P can lead to arrhythmias in horses. Low potassium can be caused by reflux, diarrhea, polyuria, & excessive sweat loss. Horses usually have diets high in potassium. You should test the fractional discretion and a blood sample, because horses that are trying to conserve potassium the blood sample may not be enough (if a horse is trying to conserve it, it will be under 16%). High potassium can be found in a blood sample if there are some burst cells in the sample; HYPP can also cause this.
Calcium – The most common cause for low calcium in our horses is when the albumin is too low. Cantharidin (toxin in blister beetles) can cause dramatic reductions in their calcium levels. Kidney disease and muscle exertion are also common for low calcium. Calcium that is too high is really unlikely in a healthy horse – kidney disease, cancer, or too much is given orally will make calcium levels elevated.
Phosphorus – This is not a common test, but low P indicates chronic kidney disease or starvation. High levels of P is often because abnormal ratios in the diet (compared to Ca); intense endurance exercise, and possibly even bone metabolism.
That's all for now!
Next time: Choosing the Endurance Horse (PNER Convention Notes)