Physicians often use the terms acute renal failure (ARF) and acute kidney injury (AKI) interchangeably to describe an abrupt decrease in kidney function that is reversible within three months of loss of function.
"Acute kidney injury can occur in people with acute kidney diseases as well as those with chronic kidney diseases," says Garry L. Huff, MD, CCS, CCDS, AHIMA-approved ICD-10-CM/PCS trainer and president of Huff DRG Review in Eads, Tennessee. "Also, it's very important to know that acute kidney injury is not synonymous with acute kidney disease."
AKI is a clinical syndrome with any one of the following etiologies:
- Specific renal diseases (e.g., vasculitis)
- Nonspecific conditions (e.g., toxic injury)
- Extrarenal conditions and pathology (e.g., obstructive uropathy)
The Kidney Disease Improving Global Outcomes Committee (KDIGO), an international committee of nephrologists, has written guidelines for defining AKI. The KDIGO criteria have largely replaced the Risk, Injury, Failure, Loss, and End-Stage-Renal Disease (RIFLE) criteria, Huff says.
The serum creatinine level is the most reliable indicator of renal function, Huff says. "It's not the ideal one because the serum creatinine goes up. It lags behind the actual renal dysfunction. So your renal function may actually have been lower for a day or so before you see it reflected in the serum creatinine."
AKI can be and often is superimposed on chronic kidney disease (CKD). Physicians used to look at AKI and CKD as separate disease entities because they are typically caused by different disease processes and have very different courses, Huff says. However, he notes, "we have discovered that these entities are not that separate."
In fact, an episode of AKI can cause a patient to develop CKD. For the most part, people who have AKI typically recover once the physician corrects the cause. The patient could have residual damage left behind. In addition, some patients with CKD are more prone to getting an AKI. "All of these things interact," Huff says. "CKD and AKI are not totally unrelated."
Stages of AKI
AKI can be divided into three different stages:
- Stage 1 AKI: The serum creatinine must be 1.5-1.9 times greater than the baseline within a seven-day period, or there must be an increase of greater than or equal to 0.3 mg/dl over 48 hours. A urine output criterion is less than 0.5 ml/kg/hour for six to 12 hours.
- Stage 2 AKI: The serum creatinine must be 2-2.9 times greater than the baseline. A urine outpatient criterion is less than 0.5 ml/kg/hour for equal to or greater than 12 hours.
- Stage 3 AKI: The serum creatinine must be three times greater than the baseline, or there must be an increase in serum creatinine equal to or greater than 4 mg/dl, or there must be initiation of renal replacement therapy. A urine output criterion is less than 0.3 ml/kg/hour for equal to or greater than 24 hours.
Note that stage 1 AKI has two definitions. "We're looking for a creatinine that is at least 1.5 times the baseline, and this has to occur within a seven-day period," Huff says. "Once we know what their baseline is, then we're looking for a value within that seven-day period that is 1.5 times the baseline."
Alternately, the patient could have an increase in serum creatinine of 0.3 mg or greater over 48 hours. "We just need to know that from day 1 to day 3 that it increased by 0.3 mg," Huff says. This definition is easier to apply because it does not require the physician to establish and document a baseline, as he or she must do for the serum creatinine definition.
"Your baseline is your optimal position," he says. "So you can use the lowest serum creatinine that's demonstrated during that hospital stay or the one that's documented by the physician if it's lower."
ICD-9-CM coding for AKI
Coders will use ICD-9-CM code 584.9 for nontraumatic acute kidney injury. ICD-9-CM also includes codes for AKI with:
- Lesion of tubular necrosis, which includes lower nephron nephrosis, renal failure with (acute) tubular necrosis, acute tubular necrosis (ATN), and tubular necrosis NOS (584.5)
- Lesion of renal cortical necrosis (584.6)
- Lesion of renal medullary [papillary] necrosis, which includes necrotizing renal papillitis (584.7)
- Other specified pathological lesion in kidney (584.8)
Coders must pay attention to coding guidelines when AKI exists in the presence of coexisting and/or coequal conditions, says Kim Yelton, RHIA, CCS, CDIP, AHIMA-approved ICD-10-CM/PCS trainer and coordinator of client education services for Huff DRG Review.
The ICD-9-CM Official Guidelines for Coding and Reporting address the sequencing of AKI based on the etiology. The first guidance deals with AKI secondary to dehydration when both are present on admission. Coding Clinic, Third Quarter 2002, pp. 21-22, instructs coders to sequence the AKI as the principal diagnosis.
"Sometimes in these medical records we might only see a diagnosis of dehydration, and that's when we need to go reference those creatinine levels to see if that patient also happens to meet KDIGO criteria," Yelton says. "Then we would have a potential query for AKI, obviously in a non-leading manner, to that physician."
If sepsis is the etiology of the patient's AKI, then sepsis should be sequenced as the principal diagnosis with AKI as a secondary diagnosis, Yelton says.
In patients who undergo a kidney transplant, coders would assign code 996.81 for the complication of a kidney transplant as principal diagnosis. "We're going to be following that with the AKI diagnosis, which will serve as a CC," Yelton says.
For patients with AKI due to rhabdomyolysis, coders should sequence AKI as the principal diagnosis, according to Coding Clinic, Third Quarter 2002, p. 28.
For benign prostate hypertrophy (BPH) with obstruction and AKI, Coding Clinic, Second Quarter 2002, p. 28, instructs coders to report AKI as the principal diagnosis based on the focus of care in the question Coding Clinic addressed. "However, we feel if the BPH is treated surgically-for example, let's say with a TURP [transurethral resection of the prostate]-then we could sequence that BPH as principal, and we would base that on our official Coding Guidelines of principal diagnosis selection, which would then take precedence," Yelton says.
AKI coding in ICD-10-CM
In ICD-10-CM, coders will have a variety of codes to choose from, depending on the information documented in the record. Coders will report both AKI and ARF using code N17.9 (acute kidney failure, unspecified), which is a CC, Yelton says. Similarly, acute renal insufficiency and acute kidney disease are both reported with code N28.9 (disorder of kidney and ureter, unspecified).
Acute tubular necrosis and vasomotor nephropathy both fall under N17.0 (acute kidney failure with tubular necrosis), which is an MCC. For drug- and heavy metal-induced tubulo-interstitial and tubular conditions, coders will report N14.X, with the fourth digit identifying the substance causing the condition.
"Currently in ICD-9, if you were to assign toxic nephropathy, that's the same diagnosis of our ATN, and that serves as an MCC," Yelton says. Acute interstitial nephritis as currently coded in ICD-9-CM also serves as an MCC. "However, when we transition over to ICD-10, we're going to lose those MCCs if these diagnoses are used as secondary. The toxic nephropathy is no longer going to be an MCC, and in fact, it's also not a CC. The acute interstitial nephritis that's currently an MCC will only be a CC in ICD-10."
This change will affect the MS-DRGs. Acute interstitial nephritis (N10) will map to MS-DRGs 689-690 instead of MS-DRGs 698?700, while toxic nephropathy (N14.X) will map to MS-DRGs 698-700 instead of MS-DRGs 682?684. Coders will report acute interstitial nephritis using code N10 (acute tubulo-interstitial nephritis). This condition also counts as a CC, Yelton says. Use code N19 for unspecified kidney failure. The good thing is that ICD-10-CM does not include any changes or additions to chapter-specific official guidelines for coding and reporting, Yelton says.
Editor’s note: This article was originally published in the July issue of Briefings on Coding Compliance Strategies. Email your questions to associate product manager Michelle A. Leppert, CPC, at mleppert@hcpro.com.