Infection, Inflammation & Blood Counts (CBC)

While the chemistry panel tells us about organ function, the Complete Blood Count (CBC) tells us about the cells themselves: the soldiers (White Blood Cells), the oxygen carriers (Red Blood Cells), and the clotters (Platelets).

For a cat with Chronic Kidney Disease (CKD), the CBC is vital for two specific reasons:

  1. Anemia: Kidneys are responsible for telling the body to make red blood cells. When they fail, anemia follows.

  2. Hidden Infection: CKD cats are prone to silent infections (like Pyelonephritis) that might only show up here.

Here is your guide to decoding the blood cells.

1. The Red Blood Cells (RBCs): The Oxygen Carriers

This is often the most depressing part of a CKD lab report. Kidneys produce a hormone called Erythropoietin (EPO), which tells the bone marrow to make more red blood cells. As kidneys scar, they stop making EPO. The result is Non-Regenerative Anemia.

HCT (Hematocrit) or PCV (Packed Cell Volume)

  • Normal: 30–45%

  • What it is: The percentage of the blood volume that is actual red cells.

  • The CKD Reality: Most advanced CKD cats are anemic.

    • Mild Anemia (20–30%): The cat usually adapts and acts normal.

    • Severe Anemia (< 20%): The cat will be lethargic, weak, have a poor appetite, and seek heat (sleeping on vents). Their gums will look pale pink or white.

    • The Treatment: If HCT drops below 20%, vets often prescribe DARBepoetin injections to replace the missing hormone and stimulate the marrow.

Reticulocytes

  • Normal: < 50,000 /µL (Variable)

  • What it is: Baby red blood cells.

  • The Clue: This tells us why the cat is anemic.

    • High Reticulocytes (Regenerative): The marrow is working hard! The anemia is likely from bleeding or hemolysis (cells bursting).

    • Low Reticulocytes (Non-Regenerative): The marrow is "asleep." This confirms the anemia is caused by CKD (lack of EPO).

2. The White Blood Cells (WBCs): The Immune System

The WBCs are your cat's defense force. In CKD, we look at them to find "silent" infections that might be causing a sudden crash.

Total WBC Count

  • Normal: 5.5–19.5 × 10³/µL

  • High (Leukocytosis): Usually infection or severe stress.

  • Low (Leukopenia): Viral disease (like Panleukopenia/FeLV) or severe, overwhelming infection (sepsis) where the body has run out of soldiers.

Neutrophils (The Infantry)

  • Normal: 2.5–12.5 × 10³/µL

  • What they are: The primary bacteria fighters.

  • High: Bacterial infection or inflammation.

  • The "Left Shift": This is a critical medical term. It means the bone marrow is releasing immature neutrophils ("bands") because the infection is so severe it can't keep up.

    • In CKD: If you see a "Left Shift," assume there is a serious infection (like a kidney infection) even if the cat has no fever.

Lymphocytes (The Specialists)

  • Normal: 1.5–7.0 × 10³/µL

  • What they are: They fight viruses and make antibodies.

  • Low (Lymphopenia): Very common in sick cats due to Stress. Cortisol (the stress hormone) kills lymphocytes. A "Stress Leukogram" is a high Neutrophil count combined with a low Lymphocyte count.

Eosinophils (The Allergy Squad)

  • Normal: 0–1.5 × 10³/µL

  • High: Suggests worms (parasites), fleas, asthma, or allergies.

3. The Platelets: The Clotting Crew

Platelet Count

  • Normal: 200–500 × 10³/µL

  • What they do: They plug holes in blood vessels to stop bleeding.

  • The "Clumping" Problem: Cats have "sticky" platelets. During the blood draw, they often clump together. The machine counts one giant clump as "one cell," leading to a falsely Low platelet count.

    • The Tip: If the report says "Low Platelets" but also notes "Platelet Clumping Present," ignore the low number. Your cat is fine.

  • True Low (Thrombocytopenia): If truly low (< 50,000), the cat is at risk of spontaneous bleeding (nosebleeds, bruising).

Summary for the Caretaker

  • Check the HCT: If it is trending down toward 20%, ask your vet about anemia treatments before the cat stops eating.

  • Check the Neutrophils: If they are high or have a "left shift," hunt for an infection (urine culture, dental exam).

  • Ignore the Platelets: Unless your cat is bleeding, a low number is usually just a lab error.

References

  • Chalhoub, S., et al. (2011). The use of erythropoiesis-stimulating agents in cats. Journal of Veterinary Internal Medicine, 25(5), 1058–1065.

  • Harvey, J. W. (2012). Veterinary Hematology: A Diagnostic Guide and Color Atlas. Elsevier Health Sciences.

  • Sparkes, A. H., et al. (2016). ISFM Consensus Guidelines on the Diagnosis and Management of Feline Chronic Kidney Disease. Journal of Feline Medicine and Surgery.

  • Stockham, S. L., & Scott, M. A. (2008). Fundamentals of Veterinary Clinical Pathology. Iowa State Press.