Coding Impact on PDGM Grouping Models – Case Mix Groups


As the first year of PDGM has unfolded there have been many twists and turns in the new complexity of coding in home care.

Many of the diagnosis codes we had been utilizing in home health, are no longer allowed as a primary diagnosis, called unacceptable primary diagnoses.

The key to accurate coding under PDGM is to have very specific documentation from your physicians / referral sources!  Ensure that if an unacceptable primary diagnosis is given by the referral / physician, that you ask for the underlying cause – often the underlying cause is an acceptable primary diagnosis.


CMS Expectations for Coding Specificity 


The following are some of the guidelines that CMS spelled out in the November 2018 Federal Register that must be followed for coding under PDGM.

  • Whenever possible, the most specific code that describes a medical disease, condition, or injury should be documented.
    • Generally, ‘‘unspecified’’ codes are used when there is lack of information about location or severity of medical conditions in the medical record.
    • Provider is to use a precise code whenever more specific codes are available.
  • If additional information regarding the diagnosis is needed, the HHA is to follow-up with the referring provider in order to ensure the care plan is sufficient in meeting the needs of the patient.
  • Vague principal diagnosis does not clearly identify the primary reason for home health, and subsequently leads to ambiguous resource use.​
  • A home health clinician should not report an ‘‘unspecified’’ code if that clinician can identify the laterality or site of a condition.
  • Many symptom codes, such as pain or contractures cannot be used as the primary diagnosis: For example,  5, Low back pain or M62.422, Contracture of muscle, right hand, although site specific, do not indicate the cause of the pain or contracture.   In order to appropriately group the home health period, an agency will need a more definitive diagnosis indicating the cause of the pain or contracture, as the reason for the skilled care.
  • R Codes (which are symptoms, signs, and abnormal clinical and laboratory findings, not elsewhere classified) are not allowed as a primary diagnosis, except for a few dysphagia codes. In the CY 2020 Final Rule, CMS determined that given the current lack of other definitive diagnoses to describe certain forms of dysphagia, the R-codes to describe dysphagia would be acceptable for reporting the primary reason for home health services. Therefore, the following R-codes will be assigned to the Neuro Rehab clinical group:
    • R13.10, R13.11, R13.12, R13.13, R13.14 & R13.19 – Multiple Dysphagia codes
  • CMS recognizes that the coding guidelines allow for the reporting of signs, symptoms, and less well-defined conditions, however, HHAs are required to establish an individualized plan of care in accordance with the home health CoPs at § 484.60.
  • CMS believes that the use of symptoms, signs, and abnormal clinical and laboratory findings would make it difficult to meet the requirements of an individualized plan of care.
    • Clinically it is important for home health clinicians to have a clearer understanding of the patients’ diagnoses in order to safely and effectively furnish home health services.
    • For patient safety and quality of care, it is important for a clinician to investigate the cause of the signs and/or symptoms for which the referral was made.
    • This may involve calling the referring physician to gather more information in order to establish the underlying cause.
  • Muscle weakness is another unacceptable code as a Primary Diagnosis under PDGM. CMS has stated that:
    • M62.81, ‘‘Muscle weakness, generalized’’ is extremely vague.
    • Generalized muscle weakness, while obviously a common condition among recently hospitalized patients does not clearly support a rationale for skilled services and does not lend itself to a comprehensive plan of care.
    • If there is not an identified cause of muscle weakness, then it would be questionable as to whether the course of therapy treatment would be in accordance with accepted professional standards of clinical practice.
    • CMS identified ‘‘muscle weakness (generalized)’’ as a nonspecific condition that represents general symptomatic complaints in the elderly population.
  • S and T codes
  • There are many of the S and T codes where the fracture and/or injury is unspecified, but the site is specified.
    • CMS maintains that the site of injury and/or fracture should be identified; however, the treatment or intervention would likely not change based on the exact type of injury or fracture.
    • Many of these codes are appropriate to group into a clinical group, and are assigned to either the musculoskeletal group or the wounds group.


Clinical Groupings – Primary Diagnosis


With the PDGM Final Rule CMS posted a complete list of ICD–10–CM codes and their assigned clinical groupings.

  • Based on the primary diagnosis, each 30-day period is placed into one of the 12 clinical groupings – HHAs should be familiar with codes that are used to group 30- day periods of care into the 12 clinical groupings.
  • If the primary diagnosis does not fit into one of the 12 clinical groups in the payment model, this is considered a “Unacceptable Diagnosis”.
  • Some additional notes are:
      • CMS states that the ICD–10–CM code list is an exhaustive list that contains many codes that do not support the need for home health services and so are not appropriate as principal diagnosis codes for grouping home health periods into clinical groups.
  • Under PDGM, if a claim is submitted by an agency with a primary diagnosis that does not fit into one of the 12 clinical groupings, the claim will be sent back to the agency as an RTP-Return to Provider. The agency will then need to review and resubmit the claim with a more appropriate primary diagnosis which does fit into a clinical grouping.
      • Furthermore, it is required per §409.43(c)(4) that any changes in the plan of care must be signed and dated by a physician. If a claim is returned for more specific coding, then it is expected that the diagnosis on the plan of care will be corrected with a signed order.


Comorbidities in PDGM


  • Coding is critical as two of the five categories for a PDGM HIPPS code results from diagnoses in the primary and secondary spots. PDGM includes comorbidities, which are defined as medical conditions coexisting with a principal diagnosis. They are tied to poorer health outcomes, more complex medical needs management and a higher level of care.
  • The premise is that by having the presence of home-health specific comorbidities as part of the overall case-mix adjustment, the reimbursement will account for differences in resource use based on patient characteristics. 3 comorbidity adjustment levels
  • No comorbidity adjustment: No secondary diagnoses exist or none meet the criteria for a low or high comorbidity adjustment.
  • Low comorbidity adjustment: There is a secondary diagnosis on the home health specific comorbidity subgroup list that is associated with higher resource use.
  • High comorbidity adjustment: Two or more secondary diagnoses on the home health specific comorbidity subgroup interaction list that are associated with higher resource use when both are reported together compared to if they were reported separately. The two diagnoses may interact with one another, resulting in higher resource use.
  • One comorbidity adjustment is permitted per 30- day period regardless of the number of secondary diagnoses or high comorbidity subgroup interactions reported on the claim. The highest level will be assigned.


Comorbidity Subgroups


  • There are 14 subgroups that can receive a low comorbidity adjustment
  • There are 31 High Comorbidity Adjustment Interaction Subgroups, however, 20 of the subgroups have interactions with either a non-pressure chronic ulcer or with a pressure ulcer. This includes diseases of arteries, arterioles and capillaries with ulceration and non-pressure, chronic ulcers or a pressure ulcer which includes stages two through four and unstageable pressure ulcers. Therefore, in only 11 of the interaction subgroups for a high comorbidity adjustment can the patient be without a non-pressure ulcer or a pressure ulcer.

Diagnoses Sequencing


  • Sequencing of the diagnoses, knowing which is primary and which are secondary, can be complex. Coding Guidelines from the ICD-10-CM Official Guidelines for Coding and Reporting should always be followed. That can mean that a diagnosis which is the primary reason for home health and documented by the physician on the face-to-face encounter could actually be in the first secondary diagnosis, rather than the primary, due to such rules as manifestation/ etiology codes or “code first” coding instructions. The primary service, highest frequency of discipline, etc. must be taken into account when assigning a primary diagnosis. Considering all of these factors, there can be variations in the diagnoses sequencing.
  • In addition to coding guidelines, the 2020 PPS final rule, the OASIS, and the CoPs give instructions for comorbidity coding that are not exactly the same, leading to confusion for agencies and coders alike. The ICD–10–CM Coding Guidelines define “other” (additional) diagnoses as “all conditions that coexist at the time of admission, that develop subsequently or that affect the treatment received and/or the length of stay.”  The OASIS D-1 Guidance Manual instructions state that “secondary diagnoses are comorbid conditions that exist at the time of the assessment, that are actively addressed in the patient’s plan of care or that have the potential to affect the patient’s responsiveness to treatment and rehabilitative prognosis.”  The CoPs at §484.60 state that the home health plan of care must include all “pertinent diagnoses’’ and the accompanying interpretive guidelines state that this means that all ‘‘known diagnoses.”
  • There are differences between the various descriptions, however, in the 2020 PPS final rule CMS stated that these instructions essentially describe the same thing:
      • “All of these coding instructions state to include any conditions that exist at the time of home health admission or that develop during the course of a home health period of care and that affect patient care planning.”
      • “Diagnoses should be reported that affect or potentially affect patient care(and therefore would be addressed in the home health plan of care), even if such care includes observation and assessment (for actual or potential effects), teaching and training or direct patient care interventions.”
      • Therefore, comorbidity/secondary diagnosis coding often will include diagnoses that affect or potentially affect patient care and those that will be addressed in the home health plan of care.


  • In order to capture correct comorbidity adjustments, you can see how important it is to receive all of the clinical history from the referral source, confirm the diagnoses with the physician, and code per coding guidelines.



Ultimately, CMS believes that precise coding allows for more meaningful analysis of home health resource use and ensures that patients are receiving appropriate home health services as identified in an individualized plan of care.  Call us today to get assistance with your home care ICD-10 coding!


As your Home Care and Hospice partner, we work together with your agency to create custom solutions that guide you through the challenges of a constantly-changing industry and prepare you for success no matter what. If you should find that you need our assistance, in any capacity, please don’t hesitate to contact us


This article also appeared in Home Health Line. The all-in-one business-building solution for home health agency executives.