Part 3: Clinical Indicators for Acute Kidney Injury/Failure | AKI Series

In the first parts of this series we looked at definitions of AKI/ARF, causes, coding and sequencing. In Part 3, we will look at what clinical indicators would possibly be present to support the diagnosis of AKI/ARF. 

Common Clinical Indicators for Acute Kidney Injury/Failure:

  • Decreased urine production-less than 0.5 mL per kg per hour for more than 6 hours
  • Edema
  • Confusion
  • Fatigue/lethargy
  • Nausea/vomiting/diarrhea
  • Abdominal pain
  • Metal taste in mouth
  • Increased BUN
  • Increased serum creatinine level-increased in greater or equal to 0.3 mg per dL or greater than or equal to 1.5 to twice the patient’s baseline
  • Increased potassium
  • Anemia
  • Proteinuria
  • Metabolic acidosis
  • Seizures
  • Coma
  • Abnormal GFR
  • Chest pain/pressure


Common Clinical Indicators for Acute Tubular Necrosis:

As we learned in the other parts of this series, acute tubular necrosis (ATN) is the most common cause of SEVERE acute renal failure, more so than acute cortical necrosis or medullary necrosis. In addition to the clinical indicators above, the following would be considered for a diagnosis of ATN:

  • Prolonged reduced renal blood flow (ischemic ATN)
  • Exposures to nephrotoxins and medications such as gentamycin, vancomycin, cyclosporine, tacrolimus, ace inhibitors, ARBS, cisplatin
  • Oliguric or on-oliguric
  • May require dialysis
  • Rhabdomyolysis, hemoglobinuria, aminoglycosides in toxic ATN
  • Sepsis, cardiogenic shock, hypovolemia, hypotension, vasoconstriction and postoperative status in ischemic ATN
  • Hypoperfusion causing cell injury in ischemic ATN
  • Acute decrease in GFR from tubular epithelial cell death and obstruction from casts and debris in the tubule lumen accompanied by a sudden increase in creatinine and BUN


Common Treatments for AKI/ARF including ATN:

  • Fluid resuscitation
  • Correction of electrolyte imbalances
  • Avoidance of nephrotoxic medications/contrast media
  • Dialysis if serious
  • Treatment of the underlying condition that is causing
  • Optimizing cardiovascular function


Three Main Criteria Used for Validation of AKI/ARF:

  • RIFLE Classification—Risk, Injury, Failure, Loss and End-stage kidney disease. Established and published in 2004. Created with primary goal to develop a consensus and have evidence-based guidelines for the treatment and prevention of AKI. (See criteria reference below)
  • AKIN Classification—Acute Kidney Injury Network. Established and published in 2007. This is a  modified version of the RIFLE criteria. This was established in order to increase the sensitivity and specificity of the diagnosis of AKI. AKIN advised that acute renal failure be changed to acute kidney injury to represent the full spectrum of renal injury (mild to severe). (See criteria reference below)
  • KDIGO Classification—Kidney Disease Improving Global Outcomes. Released in 2012 for use and is a build off of the RIFLE and AKIN criteria already being used. This criteria reserved the baseline creatinine that was established in RIFLE and a small increase in creatinine from AKIN. This is thought to give KDIGO greater sensitivity than RIFLE or AKIN. (See criteria reference below)


All three of the criteria listed above are comparable and excellent for use in diagnosing AKI. Coders should know which criteria their facility is using for diagnosing AKI so that they can be sure that the diagnosis given by the physician is clinically validated. There is no one criteria that is mandatory for use.

One of the most challenging areas that coders face today is knowing when a query is necessary. Coders see diagnoses that are documented by the physician in the medical record, and they want to be able to report the code for the diagnosis. However coders know they must clinically validate diagnoses and if they are not able to, query or get CDI or a physician liaison involved.

There is an OCG stating: “The assignment of a diagnosis code is based on the provider’s diagnostic statement that the condition exists. The provider’s statement that the patient has a particular condition is sufficient. Code assignment is not based on clinical criteria used  by the provider to establish the diagnosis.”


Does this mean coders may report any condition documented within a medical record?

No, of course not. All coders have seen copy/paste in medical records and problem lists that are brought in from previous admissions. When reporting a diagnosis, the condition must meet the reporting guidelines either for selection of PDX or as an additional SDX. The statement in the OCG above doesn’t mean that there doesn’t have to be clinical indicators for a disease present at all, only that the physician is not limited to a specific set of clinical criteria he can use to make a diagnosis. There are many “established” criteria for many diseases and AKI is no different. As above, there are three for AKI at this time.

What makes this so hard for coders is that it is difficult to question a physician’s documentation. When conflicting documentation within the record is present, that is much easier because coders are just asking for clarification. If a coder asks a physician “does this patient really have AKI/ATN?”, this could be a bad situation with a very negative outcome on the query. It is better to ask the physician what criteria were used to make the diagnosis of AKI or involve CDI or a physician liaison for help with these. Physician education is needed, and if coders don’t query, then the facilities and physicians will not know that there is a documentation issue. Physician’s should be aware and/or part of the decision on which criteria will be used for diagnosing a certain condition.

Be on the lookout for Part 4 of this series. We will be looking at what documentation is needed to report AKI, and see some examples of when a query is needed.



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.

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