The capacity of ICD-10-PCS: How much room is there really? (continued)

June 1st, 2018 / By Rhonda Butler

In my most recent blog, I discussed in general why the capacity of ICD-10-PCS has limits, and how multi-axial structure and hierarchy together define those limits. This time I’m going to get nitty-gritty about PCS capacity—describe where the system is pretty filled up already but where it is not a problem, where the system has plenty of room, and where the system is susceptible to running out of room. As with the previous blog, I will use the Med/Surg section for most examples, since it is the largest section and the one people know best.

The system is hierarchical, and the axes of classification high in the pecking order were basically fully populated when the system was first developed, because the whole idea was to complete the system to a consistent level of detail prior to implementation. For example, all of the letters and numbers used in the first four axes of a Med/Surg section code—section, body system, root operation, and body part—were fleshed out early in the system’s history, so they are pretty much at capacity already, and that is as it should be.

For all Med/Surg codes the section is designated in the first axis as 0, so we’re all set there. In the second axis and third axis, there are 31 body systems and 31 root operations used in the Med/Surg section. Since there are 34 possible letters and numbers, in theory we could add three more body systems and three more root operations to the system. However, in practice this is not likely. The 31 body systems, such as Heart and Great Vessels, Digestive System, Upper Joints, Lower Joints, and 27 others, all divvy up the human body at roughly the same level of detail. The 31 root operations specify basic physical things that can be done to the body, like cut out all of a body part (Resection), reroute a tubular body part (Bypass), or put in a device or tissue that replaces a body part (Replacement). The PCS design goal was to create tables that were complete from the outset at a consistent level of detail, and so far the indications are that the goal was met. So, if you wanted to propose adding another body system or root operation for the Med/Surg section, you would have to have a pretty compelling reason for it.

In much of the Med/Surg section, there is little or no room left in the fourth axis of classification for more detailed body part values—the 34 available letters and numbers have all been used in most body systems. However, there is still room in a few body systems. For example, a new body part value for Common Hepatic Duct was added to all the tables in the Hepatobiliary and Pancreas body system last year. But body systems with plenty of available letters and numbers are the exception rather than the rule.

Bottom line, in axes one through four of the Med/Surg section, though already at or near capacity, were adequately populated from the outset to yield consistent and easily aggregable data. So no news is pretty good news here.

In the fifth axis of classification—used to specify the approach—there is tons of room in the Med/Surg and all the other sections that use approach. Out of 34 available numbers or letters, only seven are used as approach values. Early versions of PCS had about three times as many approach values as there are now. This is why the list of approach values skips numbers, for example, from 0 Open, to 3 Percutaneous, because the approach values 1 Open Intraluminal and 2 Open Intraluminal Endoscopic were “decommissioned” prior to implementation.

It will be interesting to see if the coding community is game to add new approach values to PCS in future updates. At a C&M meeting not too long ago, a proposal to introduce the approach value 5 Percutaneous Intraluminal back into the system (where it would have been useful in distinguishing an endovascular procedure from other percutaneous versions of the same procedure) got all thumbs down during the public comment period, and so no new approach values have been added in the PCS tables since ICD-10 implementation. Nevertheless, there is room to add more detailed approaches—whether it is an endovascular approach value, or a combination approach, or that whole evolving category of approaches generically called “minimally invasive.”

Another axis of classification with lots of room for expansion—in sections other than Med/Surg—is the root operation. There is plenty of room for new root operations to be defined as new, non-surgical treatments are developed. Section 6, Extracorporeal or Systemic Therapies has only 11 root operations, for things like Decompression (hyperbaric chamber), Pheresis (filtering the blood for one of its components, like platelets) and Phototherapy (light therapy for conditions like jaundice). If some cool new systemic therapy right out of Star Trek comes along, we could create a new root operation for it in section 6.

Now, finally, we come to the tricky bit—the parts of the system that are susceptible to running out of room. In the Med/Surg section, that is the sixth and seventh axis of classification, the device and qualifier. Both are the focus of most new procedure code proposals at C&M meetings. Why? Because as you have learned if you have read this far, the rest of the PCS code is either fully populated (section, body system, root operation, body part) or more or less stable (approach).

Device and qualifier both have the potential to gobble up all their capacity early in the life of the system. Manufacturers of medical devices want specific data showing how well their device performs by comparison, and they need a unique device value to do that. For example, new codes were added last year to specify hip replacement with a prosthesis made of oxidized zirconium on polyethylene.

The qualifier is used to specify some level of detail other than device—often it is a specific surgical technique or additional detail about the site of the procedure. For example, this year at the March C&M meeting new codes were proposed that used the qualifier to specify when the “stent retriever” technique was used to remove thrombus from the arteries in the head and neck where they can cause a stroke.

Within a single root operation table, there are only 34 letters and numbers to spend on the device values. Many of those have already been spent, and once they are spent, that’s it for the life of ICD-10-PCS. The fact that the number 6 is used in table 0SR (Replacement of Upper Joints) to specify a hip joint prosthesis made of oxidized zirconium, does not mean that the number 6 can mean something else in table 0SR for some other lower joint. If someone invents a knee prosthesis made of duct tape and their lucky number is 6—no deal, the number 6 is already taken.

The same holds true for the qualifier. Within a single PCS root operation table, there are only 34 letters and numbers available to spend on the qualifier. No duplication allowed. Why this constraint? The constraint is inherent to the structure of PCS. You can refer back to the bit about hierarchy in the previous blog, if you like, or just remember that the structure of PCS is reflected in the ICD-10-PCS database that contains all the official content. The constraint is a pre-defined limit, just like the number of fields in a claim or any other arbitrary set of standards. Once it is defined, that is the way it is until the next version. (And we don’t want to talk about ICD-11-PCS right this second, do we?)

The challenge, when it comes to device value and qualifier value, is to spend our 34 letters and numbers wisely. In this context, intelligent maintenance of the classification requires that we grapple with difficult questions, questions that practically require a crystal ball: Whether the detail being requested is a meaningful distinction in the data for inpatient hospital reporting, whether the procedure detail will be adequately captured in the documentation so it can be coded, and whether the new device/surgical technique is likely to persist long enough for data capture to be significant and therefore useful.

Where there is some doubt about the wisdom of spending a remaining letter or number on a new device or surgical technique, this is where section X can function as a pressure valve, to relieve pressure on the rest of the system. Section X is a section called New Technology, whose structure is designed with much more flexibility and practically unlimited capacity. For reasons that I confess I don’t understand, the coding community has been against section X from day one. They have an almost aesthetic objection to it, as if because it was a latecomer, and is designed differently than the rest of the system, it violates their sense of order in the universe.

If that is the source of the discomfort with section X, my response to that objection is, yes, that’s the whole point—it is a latecomer, and it was designed to be different because we needed it to be different. And yes, of course it makes the system more complex, messier. This is to be expected. Any sort of classification system typically starts out all pristine and pretty—and goes downhill from there. When you start to use something, it ain’t brand new anymore. Just drive that brand-new car off the lot and see how long it takes before the pigeons notice. So, my feeling is, if the reaction to any of those tough questions above is equivocal, we should be creating codes in section X instead of using up the remaining capacity in the device and qualifier.

Rhonda Butler is a clinical research manager with 3M Health Information Systems.