WHAT IS A NORMAL VALUE FOR SERUM ALT ACTIVITY? D. Robert Dufour, MD, FACB, FCAP Consultant Pathologist Attending, Liver Clinic VAMC, Washington DC Emeritus Professor of Pathology
DISCLOSURE I have no conflicts to disclose
REFERENCE INTERVALS The standard approach for laboratory test reference intervals involves selecting asample of the (apparently healthy) population The central 95% of values (after excluding statistical outliers) is considered the reference interval (mean ± 1.96 sd if data has a Gaussian distribution)
REFERENCE INTERVALS Minimum requirement for laboratories is to validate that the range they use is appropriate for their population (often use what is suggested by manufacturer) Establishing reference interval requires many apparently healthy volunteers (for tests such as ALT, minimum of 400); validation only requires 20
PROBLEMS There are several problems with this approach How well did the manufacturer select appropriate individuals? How well does apparently healthy exclude clinically inaparent disease (a major problem with liver disease) Is typical actually healthy?
ALT REFERENCE LIMITS Two surveys have evaluated upper reference limits used by laboratories Neuschwander-Tetri (Arch Intern Med 2008) surveyed 11 labs, found ULN varied from 35 to 79 U/L in men and 31 to 55 in women Dutta (Hepatology 2009) surveyed 67 labs in Indiana; found ULN varied from 31-70 (with most labs having same limits for men and women)
ALT REFERENCE LIMITS In both surveys, found little difference based on instrument or method used In Dutta survey, 79% based reference limits on manufacturer s suggesetions; in only half were normal volunteers also tested (only an average of 25 individuals tested)
HOW COMPARABLE ARE ALT METHODS? Assays measure enzyme activity; changes in reaction conditions change actual values Main difference is reaction temperature, not always standardized in different labs Although there is a standardized IFCC method using pyridoxal-5 -PO4, most labs do not use this because of stability, measurement issues; in our studies, little difference in results
SELECTING RIGHT GROUP Prati Ann Intern Med 2002;137:1 Studied 6835 blood donors; excluded those with HCV or HBV markers, high glucose or lipids, or high BMI Found upper reference limit of 30 in men and 19 in women Found that this cutoff detected more persons with HCV viremia (76 vs 55%), mostly detecting milder histologic damage
SELECTING RIGHT GROUP Ruhl Hepatology 2012;55:447 Used data from NHANES Excluded persons with HCV, HBV, alcohol > 2 drinks/d (in men; 1 drink/d in women), high BMI or waist circumference, diagnosed diabetes or pre-diabetes, or A1c > 6.0% Found upper reference limit of 29 U/L in men, 22 in women to have best performance
SELECTING RIGHT GROUP Lee Hepatology 2010;51:1577 Evaluated ALT in 665 prospective liver donors with normal liver biopsy and no clinical features to exclude from reference interval (high cholesterol, TG, glucose, BMI, or HCV, HBV, ANA positivity) Mean age 25 in men, 30 in women Found ULN of 33 U/L in men and 25 in women
DOES TYPICAL = HEALTHY? For a number of parameters, values that are typical of the population have been found to be unhelathy: Blood pressure Weight Cholesterol Glucose Reference limits for these are based on health outcome studies
WHAT DATA EXIST ON HEALTH- BASED LIMITS FOR ALT?
HEALTH-BASED LIMITS Tai Hepatology 2009;49:1859 Studied 4,376 HBeAg negative carriers Most had ALT < 36 U/L (ULN), and 40% had ALT < 18 U/L Of those with lowest ALT, only 11% had steatosis, compared to 27% of those with ALT 19-36 and about 50% of those with higher levels
HEALTH-BASED LIMITS Kim BMJ 2004;386:983 Used death certificate data to determine risk of death from liver disease in almost 150,000 Korean persons with baseline ALT Compared to those with ALT < 20 U/L (ULN 35-40), relative risk of liver death was 2.5 in men with ALT 20-29, and 9.5 with ALT 30-39; in women, RR was 3.8 if ALT 20-29 and 6.6 if 30-39
HEALTH-BASED LIMITS Yuen Gut 2005;54:1610 Evaluated outcomes in 3223 HBV patients followed a median of 47 months; ULN ALT 53 U/L in men, 31 in women Compared to those with baseline ALT < 0.5x ULN (22% of total), those with ALT 0.5-1.0x ULN (31%) had significantly higher risk of liver-related complications; risk highest in those with ALT 1.0-2.0 x ULN, and decreased with higher ALT
HEALTH-BASED LIMITS Burgert JCEM 2006;91:4287 Studied 392 obese adolescents; ALT ULN 35 U/L Compared to those with ALT < 17, those with ALT 17-35 had worse glucose tolerance, insulin sensitivity, and higher triglycerides Only 48% of those with fatty liver by MRI had elevated ALT, those with fat had mean ALT of 34, compared to 15 in those without
HEALTH-BASED LIMITS Chang Clin Chem 2007;53:686 Evaluated 5237 men with normal (< 35 U/L) ALT and no evidence NAFLD on US Followed for median 2.5 yrs, 984 (19%) developed NAFLD on repeat US Compared to those in lowest quintile of ALT values (< 16), those with higher ALT had progressively higher RR of developing NAFLD on follow-up (p < 0.001 for trend)
HEALTH-BASED LIMITS Fracanzani Hepatology 2008;48:792 Evaluated liver biopsy findings in 458 persons with NAFLD, most biopsied for high ALT (> 40 U/L) NASH present in 59% with normal ALT versus 74% with high (p < 0.01) Only 27% of those with NASH and normal ALT had values > 30 in men or 19 in women
SUMMARY Currently, labs use very different ULN, making comparison difficult, even though there is not much difference in actual values If persons with low likelihood of liver disease excluded, ULN around 30 in men and 20 in women In those at risk for liver disease, risk of complications increases at much lower levels in many studies (15-20)
SUMMARY Based on experiences with cholesterol, glucose, A1c, change to health-based reference limits requires support of professional societies of clinicians AND laboratorians Together can address both health implications and laboratory procedures needed to assure comparable results between labs