HALT-C Formula for Predicting Cirrhosis
Our predictive model relies on a few standard laboratory values that are routinely available in patients with hepatitis C - platelet count, AST/ALT ratio and INR*.
The regression formula for predicting odds of having cirrhosis is as follows:
log odds (predicting cirrhosis) =
-5.56 - 0.0089 x platelet (x103/mm3) + 1.26 x AST/ALT
ratio + 5.27 x INR.
The formula to calculate predicted probability is exp(logodds)/(1+exp(logodds)).
Our model performed well in the objective of predicting histological cirrhosis in our population of >1,100 well-characterized patients with chronic hepatitis C and advanced fibrosis. A cutoff predicted value of < 0.2 to exclude cirrhosis, would misclassify only 7.8% (24/309) of patients with cirrhosis (negative predictive value of 85%), while a cutoff predicted value of >0.5 to identify patients with cirrhosis, would misclassify 14.8% (70/474) of noncirrhotics (positive predictive value of 75%). Approximately half, 48.5%, of the patients fell between the two cutoff values and would not be classified accurately. A cutoff of 0.6 would lead to misclassification as cirrhotic in 8.0% (38/474) of noncirrhotics, but would increase the proportion of patients that would not be classifiable to 59.3%.
The ranges used in our analysis are as follows:
Platelets 39-442
INR 0.8 - 1.6
AST 18 - 789
ALT 15 - 772