From the Guidelines
Low Creatine Kinase (CK) levels are typically caused by reduced muscle mass, low dietary protein intake, and certain demographic factors such as old age and female sex.
Factors Affecting CK Levels
- Reduced muscle mass, which can be due to various factors such as muscle-wasting conditions, amputation, malnutrition, and critical illness 1
- Low dietary protein intake, particularly cooked meat 1
- Demographic factors, including old age and female sex 1
- Ethnicity, with some studies suggesting that black individuals have higher CK levels than South Asian and white individuals 1
Clinical Considerations
It is essential to consider these factors when interpreting CK levels in clinical practice, as they can affect the accuracy of diagnosis and treatment. For example, a low CK level in an individual with reduced muscle mass may not necessarily indicate a lack of muscle damage, but rather a reflection of their underlying muscle mass 1.
Laboratory Considerations
Laboratory assays can also be affected by various factors, including hemolysis, icterus, and delayed separation, which can lead to erroneous results 1. Therefore, it is crucial to follow good laboratory practices to ensure accurate and reliable results.
Sports Medicine Considerations
In the context of sports medicine, CK levels can be influenced by exercise-induced muscle damage, and the interpretation of CK levels can be complex due to various confounding factors, including ethnicity, body composition, and exercising intensity 1.
From the Research
Causes of Low Creatine Kinase (CK) Levels
- Low serum creatine kinase (CK) activity has been observed in various conditions, including rheumatic diseases 2, 3, critically ill patients 4, and hypothyroidism 5
- In rheumatic diseases, low CK levels are associated with muscle weakness and inflammatory activity 2, 3
- In critically ill patients, low CK activity is an independent predictor of mortality and is associated with higher severity of illness 4
- In hypothyroidism, low CK levels are more commonly found in overt hypothyroidism than in subclinical hypothyroidism, and CK levels decrease to normal after thyroid function normalizes with treatment 5
- Some studies suggest that low CK levels may be associated with muscle atrophy or reduced muscle mass, but this relationship is not fully understood 2, 3
- Other factors that may contribute to low CK levels include age, gender, and physical activity level, although the evidence for these factors is limited 6
Conditions Associated with Low CK Levels
- Rheumatoid arthritis (RA) 2, 3
- Systemic lupus erythematosus (SLE) 2
- Spondyloarthropathies (SpA) 2
- Polyarthralgia/arthritis (Poly) 2
- Critically ill patients 4
- Overt and subclinical hypothyroidism 5
Laboratory Findings
- Low serum CK activity is often accompanied by other laboratory abnormalities, such as elevated erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), and lactate dehydrogenase (LDH) 2, 3
- CK levels may be correlated with other muscle enzymes, such as aspartate aminotransferase (AST) and alanine aminotransferase (ALT) 2