What should you call that elevated Creatinine?

That’s the easy question.

But what is their baseline?! That’s tougher.

The problem?

• People don’t know criteria for AKI

• Determining baseline Cr is unclear

• ATN is underdiagnosed

• Poor documentation sabotages your AKI diagnosis

1 / What is Acute Kidney Injury?

This is rather simple. It is:

• A Cr increase at least 1.5 times baseline OR

• ≥ 0.3 mg/dl increase within 48 hours

• Urine volume < 0.5 ml/kg/h for 6 hrs

Note: A Cr decrease of 0.3 cannot be used to diagnose AKI (sorry).

That’s easy. But what is baseline? THIS gets complicated but is the most important.

2 / How to determine Cr baseline?

For AKI, the baseline must be “known or presumed” to have occurred within the prior 7 days.

(7 days = the acute in Acute Kidney Injury)

So, what is considered baseline?

Baseline is determined by “review of prior record.”

But KDIGO does not clearly define this.

• Is it the lowest Cr within the past year?

• Or the most recent outpatient Cr?

• Or an average of their Cr within the last year?

A recent study in Denmark looked at this…

The take-home points:

• All definitions of baseline result in similar outcomes.

• NOT defining a baseline (aka not recognizing they had AKI) = higher morbidity.

If no prior Cr lab data is available, a baseline Cr can be defined by:

1. Lowest Cr during hospital stay

2. The MDRD equation (more in Q/A below)

A decrease can be evaluated by the patient’s SCr divided by 1.5 to determine the decrease necessary to meet criteria

3 / What about Acute Tubular Necrosis?

This is underdiagnosed.

Why? It is often a retrospective diagnosis. ATN can be diagnosed if AKI persists > 3 days after fluid resuscitation.

But there’s other criteria (do not need all):

• Associated hypotension, sepsis, or nephrotoxins (contrast, rhabdomyolysis, medications)

• UA with muddy brown casts, proteinuria, or epithelial casts

• FENA > 2% (MUST BE OLIGURIC)

You. Do. Not. Need. muddy brown casts for ATN. You can document “possible”, suspected, etc.

Documentation Tips:

• Do not give a RANGE for baseline. Pick a number.

• Don’t use “acute renal insufficiency”

• If someone has AKI on CKD, specify as such + stage of CKD

• AKI is a CC; ATN is an MCC (more below in Q/A)

In summary:

1. AKI is:

• increase of Cr to ≥1.5x the baseline Cr

• ≥ 0.3 mg/dl increase within 48 hours

2. Don’t use a range for baseline

3. Determine baseline by review of previous data or lowest Cr during hospitalization.

4. Consider “suspect ATN” if Cr still not at baseline > 3 days s/p IVF resuscitation with associated risk factors.

Criteria are based on KDIGO criteria

Question / Answer

What is MDRD for estimating Cr?

The MDRD equation is a calculation of GFR based on Gender, race, age and Cr. It can also be used to determine Cr assuming a GFR of 75. This is used in studies, but I’ve never seen this used in practice. Nephrologists also say this is not used anymore. I mention it here for completeness. The lowest Cr during hospitalization is likely going to be your go-to baseline in many cases.

What is a CC? What is an MCC

Again, AKI is a CC. ATN is an MCC.

CC stands for Complication / Comorbid Condition.

MCC stands for Major Complication / Comorbid Condition.

CC increases the relative weight of a diagnosis. MCC increases the relative weight even higher. The inclusion of these may change the DRG (Diagnosis related group) which determines how much your hospital is paid. What does all this mean? Let’s do some examples:

Sepsis may have a relative weight of 1.028. Adding AKI will increase the weight to 1.28. However, adding ATN instead will raise the weight to 1.972. What does THAT really mean?

Each hospital has a unique “multiplier” called the base payment rate (BPR). So, if your hospital’s BPR is $6,000 and a DRG’s weight is 1.0 then the payment is $6,000 (6,000 x 1.0). If the DRG’s weight is 1.5 then the payment is $9,000 (6,000 x 1.5). This is the importance of adding diagnoses which increase the relative weight. Many weights are below 1.0. It’s more complicated than that based on payor…but that’s the basics.

What do insurances prefer?

I was confused about the real criteria of AKI early in my career because of varying criteria given to me by insurance companies via Peer-to-Peer calls. They like to use higher criteria such as 2 times baseline, if not higher. KDIGO criteria are well accepted, so I would send to appeals if they are denying despite meeting the above criteria.

Do I need a Cr documented the 7 days prior to a hospitalization to properly document AKI?

NO! The baseline can be presumed to have occurred within the prior 7 days.

What about using the diagnosis of “dialysis patient.”

Don’t. You WILL get a query. This is meaningless. If they have ESRD, then specify such. But some AKI’s require dialysis so “dialysis patient” is unclear and does not equal ESRD.

Why not document renal insufficiency?

Renal insufficiency is neither a CC or MCC. Documenting it will not get you the severity you are attempting to portray if you really mean AKI, ATN, etc.

Why not give a range for baseline Cr?

Insurances will take the highest Cr of the range you document. If you documented AKI because the patient met AKI criteria based on the lowest or average of that range, insurances can deny the claim using the HIGHEST of that range. Pick a number.