Low AST in Cats – Causes, Diagnosis and Vet Treatment

Wondering what a full interpretation looks like? See a sample report →

Why Is Low AST in Cats Important?

One reason for a low AST could be related to certain medications or dietary changes that affect enzyme levels. For example, some drugs used to treat liver conditions may lower AST as they support liver function and reduce inflammation. Similarly, nutritional interventions aimed at supporting liver health might also influence AST levels. In these cases, while the drop in AST is not inherently problematic, it should be interpreted alongside other markers like ALT (alanine aminotransferase) and ALP (alkaline phosphatase). These additional tests can provide a more comprehensive view of your cat’s liver health.

It’s important to note that interpreting low AST values requires considering the big picture of your cat’s health. If your veterinarian notices a consistently low AST level, they might recommend additional tests such as a complete blood count (CBC), bile acid test, or abdominal ultrasound to rule out other potential causes like malnutrition, chronic illness, or metabolic disorders. For instance, if these further diagnostic measures reveal signs of poor nutrition or an underlying condition affecting liver function, your vet may adjust the treatment plan accordingly.

Understanding why AST levels might be low is crucial because it can guide the veterinarian towards a more accurate diagnosis and appropriate management strategy for your cat’s overall health. This holistic approach ensures that no potential issues are overlooked and helps in providing the best care possible for your feline companion.

What is AST (Aspartate Transaminase)?

AST, also known as aspartate transaminase, is an enzyme found in various tissues throughout the body, including the liver and muscles. In cats, AST plays a crucial role in amino acid metabolism within cells. This enzyme facilitates the transfer of amino groups between amino acids and ketoacids, which is essential for protein synthesis and breakdown processes.

When cellular damage occurs due to injury or disease, such as inflammation or necrosis, AST can be released into the bloodstream from damaged tissues. Elevated levels of AST in cats may indicate tissue injury, particularly in liver cells (hepatocytes) or muscle fibers. However, it’s important to note that AST is not specific to liver health alone; its presence and activity are also significant in other organs.

AST is particularly important for assessing hepatocellular function because of its high concentration in the liver compared to other tissues. Elevated AST levels can suggest issues with liver cells, but they could also indicate muscle damage or disease since AST is present in muscle tissue as well. Therefore, it’s necessary to interpret results alongside other markers like creatine kinase (CK) and alanine transaminase (ALT). This helps veterinarians determine the source of elevated enzyme activity.

• Role in Liver Health: AST is involved in amino acid metabolism within liver cells. When liver cells are damaged, AST can leak into the bloodstream, leading to increased levels that may indicate hepatocellular injury. For example, conditions such as hepatic lipidosis or cholangiohepatitis syndrome could cause elevated AST levels due to liver cell damage.
• Muscle Tissue Involvement: Since AST is also present in muscle tissue, elevated levels could suggest muscle damage or disease rather than liver-specific issues. For instance, conditions like rhabdomyolysis can lead to high AST levels due to the breakdown of muscle fibers and subsequent release of AST into the bloodstream.

In cats, a low AST level does not typically have clinical significance and usually doesn’t require further investigation. However, it’s important to consider the overall health context of the cat when interpreting any blood test results. For example, if a cat is asymptomatic with no signs of liver or muscle disease, a low AST level would be expected and normal.

Normal AST Ranges for Cats

The aspartate aminotransferase (AST) is an enzyme found in various tissues, including muscles and liver. In cats, the normal reference range for AST is 17-48 U/L. This range can vary slightly depending on the laboratory used, but it generally provides a reliable baseline to assess liver or muscle health.

It’s important to note that while low AST levels are not clinically significant in cats, they should still be interpreted within the context of other clinical signs and test results. For instance, if your cat has normal AST levels alongside other markers like ALT (alanine aminotransferase) or CK (creatine kinase), it suggests there is no evidence of liver or muscle injury.

Understanding the significance of AST levels requires considering several factors. Firstly, AST levels can fluctuate due to various physiological conditions such as stress, exercise, and dietary changes. Therefore, a single low AST reading does not necessarily indicate an underlying health issue but should be evaluated alongside other clinical indicators.

• Normal: Within the reference range 17-48 U/L.
• Mildly elevated: Slightly above the normal range, indicating possible minor tissue damage but not necessarily a serious condition. This could be due to temporary factors such as recent exercise or dietary changes.
• Markedly elevated: Significantly higher than the normal range, which may suggest more severe liver or muscle injury and warrants further investigation. In these cases, additional diagnostic tests like imaging studies or biopsy might be necessary to determine the cause of elevation.

To better understand AST levels in your cat, it’s crucial to consider other relevant markers. For example, if AST is high, comparing it with ALT can help differentiate between liver disease and muscle damage. Similarly, CK should be evaluated alongside AST when muscle injury is suspected. These comparisons provide a more comprehensive picture of the cat’s health status.

It is also important to note that while low AST levels are generally not concerning, they may occasionally indicate certain conditions such as malnutrition or chronic liver disease if other clinical signs and laboratory results suggest ongoing issues. Therefore, it’s essential for veterinarians to correlate AST values with a thorough medical history and physical examination findings.

See the full reference intervals for the cat — every value cited to the laboratory document or paper it came from.

Causes of Low AST Levels in Cats

Low levels of AST (aspartate aminotransferase) are generally not clinically significant and do not point to any specific disease or condition. However, understanding the factors that can lead to low AST is important for interpreting blood test results accurately. It’s crucial to consider various potential causes when evaluating these results in cats.

• Genetic Conditions: Some cats may have genetic variations that naturally result in lower AST levels without indicating a health issue. These conditions are rare and typically do not cause clinical symptoms. Genetic testing can sometimes identify such variants, but routine screening is usually unnecessary unless there’s a family history of similar enzyme deficiencies.
• Certain Medications: Certain medications can affect liver enzyme levels, including AST. For example, some drugs used to manage chronic diseases like hyperthyroidism or diabetes might influence liver function tests, leading to low AST readings. It’s important for veterinarians to review the cat’s medication history when interpreting blood test results. Drugs such as corticosteroids and certain anticonvulsants can also impact liver enzyme levels.
• Malnutrition: Severe malnutrition or dietary deficiencies can lead to low AST levels, although this is less common in cats compared to other species. Cats with poor appetite or those that are underweight might show lower AST levels due to reduced protein synthesis and cellular turnover.

It is crucial to note that AST is not specific to liver disease; it can also reflect muscle injury or other non-hepatocellular conditions. Therefore, a low AST level does not rule out liver issues and should be interpreted alongside other markers like CK (creatine kinase) for muscle damage assessment. Additionally, ALT (alanine transaminase), ALP (alkaline phosphatase), and GGT (gamma-glutamyl transferase) levels can provide further insight into liver function.

Comparison with Other Liver Function Tests

When interpreting AST levels, it’s crucial to consider them alongside other liver function tests. This comprehensive approach helps in distinguishing between hepatocellular injury and muscle damage, which can both elevate AST levels. For instance, a low AST level does not provide specific clinical information but may suggest that the primary concern is not related to liver or muscle cell damage.

ALT (alanine transaminase) is another key marker for assessing liver health in cats. While AST and ALT are often evaluated together due to their similar roles in monitoring hepatocellular injury, they differ in their tissue distribution. ALT is more specific to the liver, whereas AST can also be found in muscle cells. Therefore, a markedly elevated ALT level with normal or low AST levels might indicate liver-specific damage rather than generalized cell injury.

ALP (alkaline phosphatase) and GGT (gamma-glutamyl transferase) are additional markers that provide insight into bile duct obstruction and cholestasis. Elevated ALP and GGT often suggest a condition like cholangitis or hepatic lipidosis, where there is significant liver inflammation or fat accumulation affecting bile flow. However, these enzymes do not directly correlate with AST levels in terms of muscle injury.

• AST: When low, it does not indicate any specific clinical significance and should be interpreted alongside other markers for a complete picture.
• ALT: A markedly elevated ALT level suggests liver-specific damage. Normal or low AST levels in this context support the idea that muscle injury is less likely to be contributing to the elevation of ALT.
• ALP and GGT: Elevated ALP and GGT indicate bile duct obstruction or cholestasis, which can occur independently of changes in AST levels. These markers are more indicative of liver inflammation or fat accumulation affecting bile flow.

In summary, while a low AST level does not provide specific clinical information on its own, comparing it with ALT, ALP, and GGT helps to pinpoint the underlying cause of any observed abnormalities. This comparative approach is essential for accurate diagnosis and appropriate treatment planning in cats presenting with liver-related symptoms.