Reference intervals are critical for the interpretation of laboratory
results. The development of reference intervals using traditional methods is
time consuming and costly. An alternative approach, known as an a
posteriori method, requires an expert to enumerate diagnoses and
procedures that can affect the measurement of interest. We develop a method,
LIMIT, to use laboratory test results from a clinical database to identify ICD9
codes that are associated with extreme laboratory results, thus automating the
a posteriori method. LIMIT was developed using sodium serum
levels, and validated using potassium serum levels, both tests for which
harmonized reference intervals already exist. To test LIMIT, reference intervals
for total hemoglobin in whole blood were learned, and were compared with the
hemoglobin reference intervals found using an existing a
posteriori approach. In addition, prescription of iron supplements
were used to identify individuals whose hemoglobin levels were low enough for a
clinician to choose to take action. This prescription data indicating clinical
action was then used to estimate the validity of the hemoglobin reference
interval sets. Results show that LIMIT produces usable reference intervals for
sodium, potassium and hemoglobin laboratory tests. The hemoglobin intervals
produced using the data driven approaches consistently had higher positive
predictive value and specificity in predicting an iron supplement prescription
than the existing intervals. LIMIT represents a fast and inexpensive solution
for calculating reference intervals, and shows that it is possible to use
laboratory results and coded diagnoses to learn laboratory test reference
intervals from clinical data warehouses.