Part 4: Conditions and health
problems identifiable on White
Blood Cell analysis
In a blood analysis, what is a Total White Cell Count?
The white blood cell count is useful for many purposes in diagnosis and treatment and also in determining a horse’s response to treatment. There are normally approximately 5,500-12,000 white blood cells per microlitre of blood in a horse. They can be measured in a blood analysis to identify different conditions and problems interfering with a horse’s health and performance.Collectively known as leucocytes, there are several different types of white blood cells in the blood including neutrophils, lymphocytes, monocytes, eosinophils and basophils.When interpreting a horse’s blood report, what are the normal blood ranges used for comparative purposes in analysis of the blood result?
It is important to be familiar with the basic range of normal blood readings in order to identify and interpret any abnormalities in a horse’s blood.
The following are the approximate ranges of normal readings (haematology) for a TB horse (The red blood cells and haemoglobin may be slightly lower in sport horses and ponies).
Red Cell Count (RBC): 8.5 - 12 .5 [Fit horses 8.5 – 13]Haemoglobin (Hb): 12-15 [Fit horses 12 – 16]Haematocrit (PCV): 35-45 [Fit horses 37 – 45]White Cell Count (WBC): 6-12 [Often higher in yearlings] Neutrophils: 2.7- 6.7 [45% – 55%] Lymphocytes: 1.5 - 5.5 [35% - 50%]Eosinophils: 0.1- 0.6 [0% - 5%] Monocytes: 0.0 - 0.2 [0% - 3%]Basophils: 0.0 – 0.36 [0% - 2%] Where a blood report shows variations in white blood cells, what types of conditions could this indicate in a horse?
The white blood cells play a major role in inflammation and fighting infection when present in a horse’s system. The total white blood cell count provides an overall number of all types of WBCs in the horse’s blood. Differential white cell count quantifies the amount and relative percentage of neutrophils, lymphocytes, monocytes, eosinophils and basophils. Neutrophils typically make up about two thirds of the total WBC count. Lymphocytes usually make up about one third of the total WBC count. A low white cell count (leucopenia), occurs in very severe infections (and in viral infections). In these cases, the white blood cells are consumed rapidly by the vigorous bacteria (or virus) and the total count decreases because consumption exceeds production. A decreased total white cell count generally could also indicate long-term stress and/or prolonged hard training, long-term use of antibiotics or anti-inflammatory drugs.A high white cell count (leucocytosis) occurs in less intense and more chronic infections depending on the level. Other possibilities include allergic response to skin infection and parasites, etc.Exercise or excitement prior to blood sampling could also cause an elevation in the white blood cells. So if the horse was stressed at the time of collection, e.g. recent excitement or exercise, this may elevate the count. In addition, the contraction of the spleen which occurs concurrently with exercise, or excitement, releases white blood cells and red blood cells into the horse’s bloodstream. How is a Differential White Cell Count used in diagnosis of conditions in horses?
In addition to an overall increase or decrease in white blood cells, increases or decreases in each type of white blood cell can lead to - and help diagnose - disorders. The differential white cell count is where the different types of white cells are counted and may indicate different types of problems. By counting the cells and examining their form, the treating veterinary surgeon can get valuable information to help diagnose a wide variety of disorders.White blood cells consist of specific types of cells which could be simplified into the following basic types:Neutrophils – front line defence cells against infection and are the most abundant of the WBCs – (two thirds of the total white cell count). Low neutrophil levels (neutropenia) is a decrease in the number of neutrophils in the bloodstream. It indicates overwhelming bacterial or viral infection, due to the cells being used up to fight the infection in the horse’s system. Increased neutrophils (neutrophilia) in the bloodstream is usually caused by inflammation. Elevated levels of neutrophils may appear post surgery, injury, severe internal haemorrhage, long-term stress, or in chronic infection. This high reading is useful in identifying/diagnosing a chronic underlying infection.Lymphocytes – have an antibody function. Decreased lymphocyte levels (lymphopenia) could indicate long-term stress, anti-inflammatory drug treatments, e.g. corticosteroids which is one of the commonest causes. Lymphocytosis is an increase in the number of lymphocytes in the bloodstream. Elevated lymphocyte levels could indicate chronic infection, severe malnutrition, convalescence from severe illness, etc.A higher normal lymphocyte level may be present especially in young animals, e.g. in normal healthy yearlings.Eosinophils – control the extent of inflammation at the site of injury de-activating inflammatory reactions and histamine. Decreased eosinophil levels could indicate inflammation, injury, infection, over-training or stress. It is a common consequence of treatment with corticosteroids in horses.Increased eosinophil levels could indicate inflammatory response, especially worms/internal parasites or an allergic reaction. However, while a high eosinophil level is a good indicator of worms/parasites, a faecal egg count is the best method for parasite diagnosis and confirmation.Basophils – contain histamine which acts to dilate the blood vessels to allow a greater volume of healing blood to injured tissue. Elevated basophil levels could indicate serious liver damage possibly due to toxins, e.g. ingestion of toxic plants.Monocytes: The monocyte is the “clean-up” cell of the body, so with chronic inflammation there usually is an increase in the number of monocytes. Monocytosis is an increase in monocytes and may be associated with long-term inflammation and the use of corticosteroids. Elevated monocyte levels may show in recovery phase from infection and or tissue damage.What types of conditions could be identified by using a combination of the Total White Cell Count and the Differential White Cell Count in a blood analysis?
Looking at the total WBC count and the WBC differential can help diagnose both the types and the stages of an inflammation.For example, with severe acute inflammation/infection, the WBC count may tend to decrease. With more slowly developing or chronic inflammation/infection, the total WBC count tends to increase. With allergic-type inflammation, increases in the numbers of eosinophils and basophils may be noted. With WBC counts, it is often more useful after a few counts have been carried out to determine a trend in the changes.In all circumstances where the blood cell count and biochemical values are outside normal ranges, the treating veterinary surgeon will carry out a full clinical examination to confirm or establish a diagnosis in a sick or poorly performing horse.Can ulcers be identified on a blood analysis?
No, a blood test will not identify an ulcer problem in a horse. A test on the faeces may be done for this purpose but it is unreliable. The only definite and reliable method of identifying ulcers is with a special three metre endoscope which is called a gastroscope.
NEXT WEEK >> Blood biochemistry and analysis in racing/performance