Liver Function Tests and their Interpretation

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Liver Function Tests and their Interpretation

B.R. Thapa, Anuj Walia

Division of Pediatric Gastroenterology, Hepatology and Nutrition, Post Graduate Institute of Medical Education and Research,

Chandigarh

ABSTRACT

Liver function tests (LFT) are a helpful screening tool, which are an effective modality to detect hepatic dysfunction.

Since the liver performs a variety of functions so no single test is sufficient to provide complete estimate of function

of liver. Often clinicians are faced with reports that do not tally with the clinical condition of the patient and they

face difficulty in interpreting the LFT. An attempt is being made to study and understand the LFT and simplify their

interpretation with algorithms.

Key words : LFT; Alkaline phosphatase; Albumin; Prothrombin time; Aminotransferases (ALT & AST)

I. INTRODUCTION

Liver has to perform different kinds of biochemical, synthetic and excretory functions, so no single biochemical test

can detect the global functions of liver. All laboratories usually employ a battery of tests for initial detection and

management of liver diseases and these tests are frequently termed “Liver function tests”, although they are of little

value in assessing the liver function per se. In spite of receiving a lot of criticism for this terminology, the phrase

‘Liver function tests’ is firmly entrenched in the medical lexicon. It might be argued that ‘Liver injury tests’ would

be a more appropriate terminology. Moreover, the clinical history and physical examination play important role to

interpret the functions. The role of specific disease markers, radiological imaging and liver biopsy can not be

underestimated.

II. USES

The various uses of Liver function tests include: Screening : They are a non-invasive yet sensitive screening

modality for liver dysfunction. Pattern of disease : They are helpful to recognize the pattern of liver disease. Like

being helpful in differentiating between acute viral hepatitis and various cholestatic disorders and chronic liver

disease. (CLD). Assess severity : They are helpful to assess the severity and predict the outcome of certain diseases

like primary biliary cirrhosis. Follow up : They are helpful in the follow up of certain liver diseases and also helpful

in evaluating response to therapy like autoimmune hepatitis.

LIMITATIONS

Lack sensitivity: The LFT may be normal in certain liver diseases like cirrhosis, non cirrhotic portal fibrosis,

congenital hepatic fibrosis, etc. Lack specificity : They lack specificity and are not specific for any particular

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disease. Serum albumin may be decreased in chronic disease and also in nephrotic syndrome. Aminotransferases

may be raised in cardiac diseases and hepatic diseases. Except for serum bile acids the LFT are not specific for liver

diseases and all the parameters may be elevated for pathological processes outside the liver.1,3 Thus, we see that

LFT have certain advantages as well as limitations at the same time. Thus, it is important to view them keeping the

clinical profile of the patient in mind.

III. CLASSIFICATION OF LIVER FUNCTION TESTS A.

Tests of the liver’s capacity to transport organic anions and to metabolize drugs- Serum bilirubin, urine bilirubin,

urobilinogen etc.

B. Tests that detect injury to hepatocytes (serum enzyme tests) – Aminotransferases, alkaline phosphatase, ã

glutamyl transpeptidase, 5 nucleotidase, leucine aminopeptidase etc

C. Tests of the Liver’s biosynthetic capacity- Serum proteins, albumin, prealbumin, serum ceruloplasmin,

procollagen III peptide, a 1 antitrypsin, a feto protein, prothrombin time etc. The clinical significance of LFT is

given in Table 1 A. Tests of the liver’s capacity to transport organic anions and to metabolize drugs.





IV. URINE BILIRUBIN

The presence of urine bilirubin indicates hepatobiliary disease. Unconjugated bilirubin is tightly bound to albumin

and not filtered by the glomerulus and thus not present in urine. Measurable amounts of conjugated bilirubin in

serum are found only in hepatobiliary disease.1 Because the renal threshold for conjugated bilirubin is low and the

laboratory methods can detect low levels of bilirubin in urine so conjugated bilirubin may be found in urine when

the serum bilirubin levels are normal. This is the case in early acute viral hepatitis.1, 6 Tests strips impregnated with

diazo reagent are easy to use and detect as little as 1-2µ mol bilirubin/L

V. UROBILINOGEN

An increase in the urobilinogen in urine is a sensitive indicator of hepatocellular dysfunction. It is a good indication

of alcoholic liver damage, well compensated cirrhosis or malignant disease of the liver. In viral hepatitis it appears

early in urine. It is markedly increased in hemolysis.3, 5 In cholestatic jaundice urobilinogen disappears from urine.

VI. CONCLUSION

A single liver function test is of little value in screening for liver disease as many serious liver diseases may be

associated with normal levels and abnormal levels might be found in asymptomatic healthy individuals. The use of





battery of liver function tests, however constitutes a highly sensitive procedure. The number of false negatives must

be reduced by this technique. The use of battery of liver tests is also associated with high specificity especially when

more than one test is abnormal. The pattern of enzyme abnormality, interpreted inthe context of the patient’s

characteristics, can aid in directing the subsequent diagnostic work-up. Awareness of the prevalence of determined

liver disease in specific populations and of possible hepatic involvement during systemic illnesses or drug therapies

may help the clinician identify the cause of alterations efficiently.

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Liver Function Tests and their Interpretation

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