Part 2: Specificity Coding of Acute Kidney Injury (AKI) and Sequencing | AKI Series

Kim Carrier RHIT, CDIP, CCS, CCS-P
Director of Coding Quality Assurance
AHIMA Approved ICD-10-CM/PCS Trainer

As discussed in Part 1 of this series, AKI/ARF is a common diagnosis that coders see daily. In Part 2, we are going to focus on the different types/specificity of AKI/ARF. We’ll learn what they mean, as well as how to code the diagnosis.

Coding AKI/ARF

There are several different codes that can be used to report the diagnosis of acute kidney injury and/or acute renal failure. This is one example of why diagnoses should not be coded by the use of only the Alphabetic Index within ICD-10-CM. It is imperative that coders also use the tabular before final determination of the code is made. If the coder only looks in the Alphabetic Index under injury | kidney | acute, the index goes to N17.9 (acute renal kidney failure, unspecified). If the type or cause of the AKI/ARF is further specified then N17.9 would not be appropriate. However, if the coder begins the search with the term “failure” there will be several selections for further specificity under failure | renal | acute.

When coding AKI/ARF, there are instructional notes within the ICD-10-CM Index for coders to follow as well as Exclude1 and Excludes2 notes. When a cause for the AKI/ARF has been identified the underlying condition/cause should be reported also. Traumatic kidney injuries are reported with codes from S37.0-.

• N17.0—Acute kidney failure with tubular necrosis. Coders see ATN (acute tubular necrosis) documented in patient records often. This is a common diagnosis that a query is necessary for clarification. If the AKI has progressed to ATN then the code N17.0 is reported and not the code default in the Alphabetic Index for AKI. Other terms that may be used to describe ATN could be renal tubular necrosis or tubular necrosis. These are terms that should be searched for when AKI is documented to see if there could be further specificity in code assignment. ATN occurs when there is damage to the kidney tubule cells. These are the cells that reabsorb fluid and minerals in the kidney from urine as it is forming. When this occurs, there is a lack of oxygen reaching the cells of your kidneys.
• N17.1—Acute kidney failure with acute cortical necrosis. This isn’t as commonly documented as ATN but coders will see this. If the AKI has progressed to acute cortical necrosis then N17.1 is reported and not the code default in the Alphabetic Index for AKI. Other terms that may be used to describe acute cortical necrosis can be cortical necrosis and renal cortical necrosis. This is a rare cause of AKI and is due to ischemic necrosis of the renal cortex. This is typically caused by diminished/reduced renal arterial perfusion. Intravascular coagulation, vascular spasm and microvascular injury are the main causes of this type of AKI.
• N17.2—Acute kidney failure with medullary necrosis This isn’t as commonly documented as ATN but coders will see this. if the AKI has progressed to with medullary necrosis then N17.2 is reported and not the code default in the Alphabetic Index for AKI. Other terms that may be used to describe acute medullary necrosis can be acute medullary [papillary] necrosis or renal medullary necrosis. This is caused by infarction involving the medulla and referred to as necrotizing papillitis.
• N17.8—Other acute kidney failure. This code is reported when there is a specificity to the diagnosis of AKI (non-traumatic) but is not one of the ones above.
• N17.9—Acute kidney failure, unspecified. This code is reported when only AKI/ARF is documented without any further specificity documented.

Sequencing of AKI/ARF

There are many different scenarios that would dictate the sequencing of AKI/ARF. The definition of PDX should always be used when determining the PDX. Remember that just because the condition may be present on admission does not necessarily mean that it is appropriate as PDX. Chapter specific guideline must be followed as well as other coding guidance that your record may require. Some of the most common specific guidelines that come to mind are sepsis, OB/delivery records and transplant complications. Let’s look at an example of each of these:

• Just in my experience, I think sepsis is one of the most common conditions that are associated with a diagnosis of AKI. If a patient presents with high fever, elevated WBC of 20,000, altered mental status. Labs show that the patient has AKI based on elevated creatinine of 4.3 that is way above the baseline for this patient and they are admitted for workup and treatment. This was a complicated stay with several physicians documenting daily. The fever and elevated WBC count is documented to be caused by sepsis. The AKI is further documented as ATN due to sepsis and there is no contradictory documentation that requires a query. The creatinine on discharge had improved to 1.1 which is the patient’s baseline. In this case, ATN would NOT be appropriate as the PDX since it is related to sepsis. There are specific guidelines that state to code the systemic infection first and then any organ dysfunction associated with the diagnosis. Sepsis would be the PDX in this case followed by severe sepsis without shock and ATN as additional SDX codes.
• Patient presents for emergency cesarean section due to heavy bleeding and suspicion of placenta abruption. She is 38 weeks pregnant. Patient does undergo the cesarean without complication other than blood loss. The abruption of the placenta is confirmed. Due to blood loss, the patient is watched closely and is noted to develop AKI/ARF on day two post discharge. This is addressed quickly with IV fluids and the patient does improve over the next few days. Her labs are better each day and the decision of discharge was made. In this case, the AKI/ARF would not be the PDX for two reasons: 1) It occurred after surgery/cesarean, and 2) OB guidelines would be followed and a code from Chapter 15 would be reported as codes from this chapter always take sequencing priority. A code from Chapter 15 for the AKI/ARF would be reported. No additional code for the AKI/ARF would be necessary since this is not further specified and the unspecified code does not provide any further specificity. Other codes for the weeks of gestation and single live birth would be reported as well as ICD-10-PCS for the cesarean.
• Patient presents with generally feeling unwell. They are four months s/p renal transplant that has been doing well during follow up visits. The patient states that she developed a virus a few days ago and has not been able to keep anything on her stomach for three days now. Patient is admitted due to symptoms and to monitor the kidney transplant status. The labs do show that the patient has AKI/ARF with creatinine extremely high at 6.1. The baseline creatinine for this patient since transplant has been 1.1-1.4. Aggressive treatment is begun and the labs show complete improvement in only 2 days of aggressive fluids. The diagnosis from the physician is AKI/ARF in a kidney transplant patient with recovery of full function by discharge. In this case, the AKI/ARF would not be appropriate as the PDX since the function of the transplanted kidney was impaired. Per recent coding guidance, this is coded as T86.19—other complication of kidney transplant and not T86.12—Kidney transplant failure since only the function of the organ was affected but the transplant has not truly failed.

Note: The old sequencing guidance from ICD-9-CM regarding AKI/ARF and dehydration has been clarified in 2019. The sequencing is based on the circumstances of admission and will be a case by case decision. There is no rule that states that the AKI/ARF must be sequenced first over dehydration.

References
cdc.gov/mmwr/volumes/67/wr/mm6710a2.htm
emedicine.medscape.com/article/1925597
americannursetoday.com/acute-kidney-injury
academic.oup.com/ck/article/6/1/8/468698
kidney.org/atoz/content/AcuteKidneyInjury#
mayoclinic.org/diseases-conditions/kidney-failure/symptoms-causes/syc-20369048
uofmhealth.org/health-library/aa115361
ICD-10-CM Alphabetic and Tabular Indexes
ICD-10-CM/PCS Coding Clinic, First Quarter 2019 Page: 12
ICD-10-CM/PCS Coding Clinic, Second Quarter 2019 Page: 7
ICD-10-CM Official Guidelines for Coding and Reporting FY 2020

Happy Coding!

The information contained in this coding advice is valid at the time of posting. Viewers are encouraged to research subsequent official guidance in the areas associated with the topic as they can change rapidly.