Is an ALT level under 0.45 considered normal?

ALT Value Under 0.45: Clinical Significance and Management

An ALT value under 0.45 U/L is abnormally low and warrants clinical attention, as low-normal ALT values (<17 IU/L) are associated with increased long-term mortality risk and may serve as a biomarker for frailty, even in middle-aged adults. 1

Understanding Low ALT Values

Clinical Significance of Low ALT:

• Low-normal ALT values (serum ALT activity <17 IU/L) predict increased risk of all-cause mortality with a hazard ratio of 1.6 (95% CI 1.34-1.92; p<0.001), independent of age, gender, kidney function, albumin levels, hypertension, diabetes, and ischemic heart disease 1
• This association remains statistically significant even after multifactorial correction for major comorbidities 1
• Low ALT levels serve as a biomarker for increased incidence of frailty and subsequent risk of mortality, not just in elderly patients but also in younger, middle-aged adults 1

Normal ALT Reference Ranges

Standard Reference Values:

• Normal ALT ranges are 29-33 IU/L for males and 19-25 IU/L for females 2
• An ALT value of 0.45 U/L is dramatically below these normal ranges, representing less than 2% of the lower limit of normal 2
• ALT is highly specific for liver tissue due to its low concentrations in skeletal muscle and kidney, making it the most liver-specific aminotransferase available 2

Clinical Implications

What Low ALT May Indicate:

• Severe nutritional deficiency or malnutrition affecting protein synthesis
• Advanced frailty syndrome with decreased muscle mass and metabolic activity
• Vitamin B6 (pyridoxine) deficiency, as ALT requires pyridoxal phosphate as a cofactor
• Chronic debilitating illness with reduced metabolic activity
• Potential marker of poor overall health status requiring comprehensive evaluation 1

Recommended Management Approach

Immediate Assessment:

• Verify the laboratory result by repeating the test, as values this low may represent laboratory error or specimen handling issues 2
• Obtain complete metabolic panel including albumin, total protein, and other markers of synthetic function 2
• Assess nutritional status including vitamin B6 levels, folate, and B12
• Evaluate for signs of frailty, sarcopenia, or chronic wasting conditions 1

Clinical Evaluation:

• Detailed assessment of dietary intake, weight loss history, and functional status
• Screen for chronic diseases that may contribute to poor nutritional status or frailty
• Consider age-appropriate cancer screening if not up to date, given the association with increased mortality 1
• Evaluate for conditions causing malabsorption or increased metabolic demands

Important Caveats

Key Considerations:

• While elevated ALT receives significant clinical attention, abnormally low ALT values should not be dismissed as "better than normal" 1
• The mortality risk associated with low ALT (<17 IU/L) persists across age groups, including middle-aged adults at mean age 48 years 1
• Low ALT may reflect systemic issues beyond liver function, including overall metabolic health and frailty status 1
• Laboratory reference ranges typically focus on upper limits; values below the lower limit warrant equal clinical scrutiny

Follow-up Strategy:

• If low ALT is confirmed on repeat testing, comprehensive nutritional and functional assessment is warranted 1
• Monitor for progression of frailty markers and consider interventions to improve nutritional status
• Long-term follow-up is important given the association with increased all-cause mortality over median 8.5-year follow-up 1