More On Diagnostic Precision

We say that a diagnosis of disease A is more precise than a diagnosis of disease B if disease A is a subtype of disease B. For example, a diagnosis of coronary artery disease is more precise than a diagnosis of heart disease, and a diagnosis of stenosis of the left anterior descending coronary artery is more precise than a diagnosis of coronary artery disease.

One big reason that ICD-10-CM proponents want to switch from ICD-9-CM is that the disease classes of ICD-9-CM are often not at a sufficient level of diagnostic precision to support many "secondary" uses of health care data, such as rewarding doctors and hospitals for improving quality of care, medical research, chronic disease management, and so on.

For sure, ICD-9-CM is not sufficient for patient care, because to treat patients you need to record the individual diseases, not the classes into which they go.

Because ICD-10-CM is also a classification of diseases, as opposed to a set of codes for individual diseases, it is likely that even with ICD-10-CM, we will still be wanting for increased diagnostic precision. Again, for patient care we need to code individual diseases, not disease classes. Thus, no disease classification will ever be sufficient for patient care.

However, already there are even secondary uses of health care data that require higher diagnostic precision than that provided by ICD-10-CM.

At least one researcher wants to study patients with type 1a diabetes mellitus, and thus wishes to exclude patients with type 1b diabetes mellitus from the study. However, ICD-10-CM does not provide codes for these two subtypes of type 1 diabetes mellitus. This researcher will not be helped by ICD-10-CM, but will still have to test all patients with type 1 diabetes mellitus to determine which subtype they have.

We need a disease-coding system, not a disease-classification coding system. We should not switch to ICD-10-CM.