Understanding LFTs

Question 1

Function of LFTs

Answer 1

To distinguish between hepatocellular injury (hepatic jaundice) and cholestasis (post-hepatic or obstructive jaundice)

Question 2

Tests used in LFTs

Answer 2

Alanine transaminase (ALT)
Aspartate aminotransferase (AST)
Alkaline phosphatase (ALP)
Gamma-glutamyltransferase  (GGT)
Bilirubin
Albumin
Prothrombin time (PT)

Question 3

Distinguishing between Hepatocellular Damage and Cholestasis

Answer 3

ALT
AST
ALP
GGT

Question 4

Assessing Liver’s Synthetic Function

Answer 4

Bilirubin
Albumin
PT

Question 5

ALT

Answer 5

Marker of hepatocellular injury

Concentrated in hepatocytes
Enters blood after hepatocellular injury

Question 6

ALP

Answer 6

Marker of cholestasis

Concentrated in liver/bil duct/bone tissues
Raised in live pathology due to incr synthesis in response to cholestasis

Question 7

ALT and ALP in Predominantly Hepatocellular Injury

Answer 7

Greater than 10-fold increase in ALT and a less than 3-fold increase in ALP

Question 8

ALT and ALP in Cholestasis

Answer 8

Less than 10-fold increase in ALT and a more than 3-fold increase in ALP

Question 9

GGT

Answer 9

Suggests biliary epithelial damage and bile flow obstruction

Raised in resp to alcohol and drugs e.g. phenytoin

Question 10

Highly raised ALP plus raised GGT?

Answer 10

Cholestasis

Question 11

Causes of Isolated Rise of ALP

Answer 11

(Anything involving bone breakdown)
Bony metastases or primary bone tumours (e.g. sarcoma)
Vitamin D deficiency
Recent bone fractures
Renal osteodystrophy

Question 12

Causes of Isolated Rise in Bilirubin

Answer 12

Gilbert’s syndrome: the most common cause.

Haemolysis: check a blood film, full blood count, reticulocyte count, haptoglobin and LDH levels to confirm.

Question 13

Investigation of Liver’s Main Synthetic Functions

Answer 13

Conjugation and elimination of bilirubin (serum bilirubin)
Synthesis of albumin (serum albumin)
Synthesis of clotting factors (PT)
Gluconeogenesis (serum blood glucose)

Question 14

Cause of Jaundice from Urine/Stool Colour

Answer 14

Normal urine + normal stools = pre-hepatic cause
Dark urine + normal stools = hepatic cause
Dark urine + pale stools = post-hepatic cause (obstructive)

Question 15

Causes of Unconjugated Hyperbilirubinaemia

Answer 15

Haemolysis (e.g. haemolytic anaemia)
Impaired hepatic uptake (e.g. drugs, congestive cardiac failure)
Impaired conjugation (e.g. Gilbert’s syndrome)

Question 16

Causes of Conjugated Hyperbilirubinaemia

Answer 16

Hepatocellular injury

Cholestasis

Question 17

Function of Albumin

Answer 17

Helps bind water/cation/FAs/bilirubin

Maintains oncotic pressure of blood

Question 18

Causes of Decreased Albumin

Answer 18

Liver disease resulting in a decreased production of albumin (e.g. cirrhosis).
Inflammation triggering an acute phase response which temporarily decreases the liver’s production of albumin.
Excessive loss of albumin due to protein-losing enteropathies or nephrotic syndrome

Question 19

Prothrombin Time (PT)

Answer 19

Measure of the blood’s coagulation tendency, specifically assessing the extrinsic pathway

Question 20

Causes of Increased PT

Answer 20

(In absence of anticoags and vit K defic)
Liver disease and dysfunction
Failure to produce clotting factors

Question 21

AST/ALT Ratio

Answer 21

ALT > AST is associated with chronic liver disease

AST > ALT is associated with cirrhosis and acute alcoholic hepatitis

Question 22

Serum Glucose

Answer 22

Measures liver’s generaton of glucose from non-carb substrates (gluconeogenesis)
One of the last to be impaired in liver failure

Question 23

Common Causes of Acute Hepatocellular Injury

Answer 23

Poisoning (paracetamol overdose)
Infection (Hepatitis A and B)
Liver ischaemia

Question 24

Common Causes of Chronic Hepatocellular Injury

Answer 24

Alcoholic fatty liver disease
Non-alcoholic fatty liver disease
Chronic infection (Hepatitis B or C)
Primary biliary cirrhosis

Question 25

Less Common Causes of Chronic Hepatocellular Injury

Answer 25

Alpha-1 antitrypsin deficiency
Wilson’s disease
Haemochromatosis