The Kidney Disease Acronym
Spectrum: ARI, CKD, AKI, ARF,
and ESRD
Trey La Charité, MD
Physician Advisor, Clinical Documentation Integrity Project and Coding
University Health Systems
Knoxville, TN
Cell: 865/250-9625
Office: 865/305-9081
Clachari@mc.utmck.edu
Topic Outline
• Basic renal anatomy/physiology
• Clinical and CDI implications of BUN & Cr
• Renal disease definitions with CDI applications
– ARF/AKI
– CKD
– ARI
– ESRD
– Emergent HD indications
• Query opportunity examples
Kidney Facts
• Each kidney about size of computer mouse or
•
•
•
•
closed fist
Nephron is functional unit of kidney
– Each kidney contains ~ 1 million nephrons
Number of nephrons naturally decreases by ~
10% every decade of life
☻Everybody gets CKD if live long enough!
Clinicians monitor blood urea nitrogen (BUN) &
serum creatinine (Cr) to assess renal function
Patients may not show any clinical signs of
disease until only 20% of nephrons remain
Kidney Structure
Nephron
Nephron Structure
Basic Renal Physiology
• Glomerular filtration rate (GFR) = amount of
blood filtered through all nephrons in 1 hour
– “Normal” GFR (eCrCl) ~ 125 cc/hr
• Ultrafiltrate moves into and through Bowman’s
capsule into nephron tubule system:
Proximal
convoluted
tubule
Loop of
Henle
Distal
convoluted
tubule
• Ultrafiltrate modified in nephron tubule system
via reabsorption, secretion, and concentration
– Only 1% of initial ultrafiltrate excreted as urine
Renal Physiology Facts
• Ultrafiltrate in Bowman’s capsule contains
•
•
•
•
‼
•
•
everything (BUN & Cr) but cells & large proteins
+
PCT reabsorbs Na , Cl , H20, AAs, glucose, vits
Loop of Henle reabsorbs H20 concentrating fluid
DCT reabsorbs urea back into blood (BUN)
Collecting duct reabsorbs H20 for further fluid
concentration & urea into blood (BUN)
Creatinine filtered & secreted in PCT
(only 5%–10%), but not reabsorbed
Normal serum BUN ~ 10–20
Normal serum creatinine ~ 1.0
What About the BUN/Cr Ratio?
• Understanding BUN/Cr ratio significance can
lead clinician to potential cause(s) of kidney
function abnormalities
☻Leads CDI personnel to query opportunities
for POA indicators, cause & effect
relationships, and missed diagnoses
– Normal BUN/Cr ratio = 10:1 to 20:1
• In assessing abnormal kidney function,
clinicians review the BUN/Cr ratio to discern if
lower, equal to, or higher than normal
– Helps suggest cause, guide needed workup,
and determine best treatment approach
Clinician Kidney Disease
Thinking
• Clinicians are taught to divide kidney disease
into 3 broad categories:
– Prerenal = problem occurs before nephron
– Intrarenal = problem occurs within nephron
– Post-renal = problem occurs after nephron
• BUN/Cr ratio suggests which category current
kidney problem likely falls into
• Knowing which category kidney abnormality falls
into can drive your query process
BUN/Cr Ratio Utility for CDI
• Prerenal ~ BUN/Cr ratio GREATER than 20:1
– Reduced blood flow equally decreases both
BUN & creatinine filtration at glomerulus
– However, urea reabsorption in DCT and
collecting duct now increases as pumps have
longer time to work on slower moving fluid
– Therefore, both values rise but BUN rises
faster than creatinine increasing their ratio
• Additional findings in prerenal pathology
– Urine Na+ < 20
– FeNa+ < 1%
– FeUrea < 35%
BUN/Cr Query Opportunities
• If prerenal (50%–70% of AKI), CDI personnel
should then be asking “Why?”
1. Volume problem
– DKA/HHNC
– Hemorrhage
– Cirrhosis/burns
– Vomiting/diarrhea
2. Perfusion problem
– CHF
– Shock (septic/cardiogenic)
BUN/Cr Ratio Utility
• Intrarenal ~ BUN/Cr ratio LESS than 10:1
– If glomeruli are damaged, BUN & creatinine
filtered less but both equally reduced
– Nephron tubule damage decreases urea
reabsorption as pumps are broken
• Serum BUN rises much slower
– Therefore, both levels rise but their ratio
actually decreases
• Additional findings in intrarenal pathology
– Urine Na+ > 40
– FeNa+ >> 1%
– FeUrea > 50%
BUN/Cr Query Opportunities
• If intrarenal (25% of AKI), why?
1. Vascular
– Vasculitis (Wegner’s)
– Nephrosclerosis
– Renal atherosclerosis
– RAS
2. Glomerular
– RPG
– IgA nephropathy
– Postinfectious
– SLE
– Membranoproliferative
3. Tubular
– Acute tubular necrosis
– Acute interstitial nephritis
– Autoimmune
– MM
Intrarenal Pathology and CDI
• Acute kidney failure codes (584.X) partially
differentiated by underlying etiology
– 584.9 = Acute kidney failure, unspecified
– 584.5 = Acute kidney failure w/ lesion of tubular
necrosis
– 584.6 = Acute kidney failure w/ lesion of renal cortical
necrosis
– 584.7 = Acute kidney failure w/ lesion of renal
medullary necrosis
– 584.8 = Acute kidney failure w/ other specified lesion
in kidney
• 584.9 is a CC while rest are MCCs
BUN/Cr Ratio Utility
• Post-renal ~ BUN/Cr ratio EQUAL TO normal
– “Normal” range = 10:1 to 20:1
– Nephron works fine but urine can’t get out of
body due to obstruction distal to kidney
– Therefore, both levels rise but rise
equivalently preserving a relatively normal
ratio between them
• Additional findings in post-renal physiology
– Renal US or CT scan ABD/Pelvis with
significant hydronephrosis proximal to
obstruction
BUN/Cr Query Opportunities
• If post-renal (5%–10% of AKI), why?
– BPH
– Prostate CA
– Bladder CA
– Metastatic malignancy (cervical/ovarian)
– Retroperitoneal fibrosis
– Retroperitoneal hemorrhage/hematoma
– Nephrolithiasis
ARF/AKI and CDI
• When a patient’s serum creatinine dramatically
rises above their baseline level, it is more than
just “dehydration” or “azotemia” or “acute
renal insufficiency”
• This is “acute renal/kidney failure”
Not “acute on chronic kidney disease”
• Must write out what “ARF/AKI” means at least
once in the chart!
– Auditors may question what ARF or AKI
means without writing out acronym one time
• ARF/AKI definition revised 8/11 by KDIGO
Acute Kidney Injury Definition
1. Any rise in serum creatinine of 0.3 mg/dl
or more above patient’s baseline ...
-Either/Or2. Any rise greater than or equal to 1.5
times patient’s baseline serum creatinine
‼ “Baseline” = lowest recorded creatinine
value for patient in preceding 3 months
www.renal.org/Clinical/GuidelinesSection/AcuteKidneyInjury.aspx*
*Note: This was updated in March 2012
ARF/AKI Query Strategy
• First, decide/verify whether patient meets
criteria of ARF/AKI
– If no, yet clinician has called this in chart, will
need clarification prior to coding
Coders not allowed to question physicians’
judgment while post-discharge auditors are allowed
– If yes, go to next step
• Second, calculate the BUN/Cr ratio
– Is problem pre-, intra-, or post-renal?
• Third, is the urinalysis helpful?
☻With this information, is there now opportunity
to further clarify why patient has ARF/AKI?
What About the Urinalysis?
• Prerenal
– Hyaline casts
• Intrarenal
1.Proteinuria
2.Cells (WBCs & RBCs)
3.Cell casts:
• WBC (AIN)
• RBC (glomerulonephritis)
• Epithelial (ATN)
• Post-renal
– Benign/no significant abnormalities
– Hematuria
Current ARF/AKI Coding
• Per KDIGO, “acute renal failure” terminology to
be replaced by “acute kidney injury”
• Problem: “AKI” currently codes to “ARF”
• Therefore, physicians should not document AKI
unless they truly mean ARF
 Watch for clinicians using AKI to describe
any acute renal abnormality even if does
not meet ARF criteria
• Some physicians will adopt this new
terminology regardless of coding implications
– May increase need for query clarifications,
so do not report ARF when not actually
present
Future ARK/AKI Coding?
• Presently, no documentation benefit for
physicians documenting stage of AKI
• Hopefully … ICD-9 or ICD-10 codes will be
created for AKI stages
• Suspect … Stages 1 & 2 will be CCs while
Stage 3 will be an MCC
• Start medical staff education of stages when
AKI codes definitively arrive
– Teaching new failure definitions tough
enough without confusing issue with stages
Chronic Kidney Disease
Def: Presence of kidney damage or decreased
kidney function persisting for at least
3 months regardless of cause
•
•
•
•
•
Stage I
Stage II
Stage III
GFR = > 90 ml/min
GFR = 60–89
GFR = 30–59
Stage IV
Stage V
GFR = 15–29
CC
GFR < 15 (but no HD/PD) CC
Chronic Kidney Disease
• In order to properly stage CKD, physicians must
either calculate CrCl or have it provided for them
• eCrCl estimates GFR via Cockcroft-Gault eq
eCrCl =
(140 - patient’s age) x patient’s wt in Kgs
72 x patient’s baseline serum creatinine
X 0.85
for
women
patient’s ideal weight = 60 Kgs for women
and 70 Kgs for men
• Reduced credit given if physician documents
“CKD” only without stage
CKD Query Opportunities
• Most important determinants of Cockcroft-Gault
equation estimation:
1. Patient’s age
2. Patient’s serum creatinine
‼ Serum creatinine greater effect than age
• Calculate CrCl for anybody with ...
– Serum creatinine > 1.0
– Age of 50 years or older regardless of
serum creatinine level
• Why?
What if Acute Rise But Not
ARF?
• In the acute setting, what does one call the “noman’s land” between a patient’s baseline
creatinine and ARF/AKI?
Patient’s
baseline
creatinine
(normal
or CKD)
?
Increasing serum creatinine
ARF
AKI
No ‘Great’ Answers
• “Azotemia” or “uremia” = 790.6, Other
abnormal blood chemistry
• “Dehydration” = 276.51
– Not accurate for creatinine rises due to intraor post-renal etiologies
• “Acute nephropathy” = 580.9, Acute
glomerulonephritis with unspecified pathologic
lesion in kidney
☻“Acute renal insufficiency” = 593.9,
Unspecified disorder of kidney and ureter
End-Stage Renal Disease
• Failure of kidneys to perform functions
necessary to support daily life
– Usually occurs when less then 10% of renal
function remains
• Patients cannot survive without routine dialysis
or a kidney transplant
– Patients qualify for permanent dialysis when
their measured CrCl is 10 mg/dl or less
☻Query opportunity for ESRD when here
– Your nephrologists may start preparing
patient for HD/PD when CrCl = 15mg/dl
• ESRD (585.6) is an MCC
Emergent HD Query
Opportunities
• Indications for emergent dialysis:
A = Acidosis
E = Electrolytes (i.e., hyperkalemia causing
cardiac arrhythmias)
I = Ingestion (beware of psychiatric codes as
principal dx)
O = Overload (Is there really acute CHF?)
U = Uremia (not really done anymore)
Y = Why? Why not because nobody understands
nephrology or nephrologists!
Renal Disease CDI Pocket Card
Example #1
• 48 yo WF comes to ED with complaints of fever,
chills, cough w/ green sputum, myalgias, and
weakness. She is tachycardic w/ T = 102.7. She
is hypotensive & requires 4 liters IVF to
normalize BP. Initial WBC = 28.7. Initial workup
reveals sepsis due to multilobar pneumonia.
Patient did notice her urine had been very dark.
Initial BUN & Cr are 32 & 3.8. Last recorded
BUN & Cr were 19 & 0.8 in PCP’s office 2
months ago. UA reveals large amount of protein
and numerous epithelial cell casts. BUN & Cr
almost normalize by time of discharge.
Example #1
• Patient initially admitted to ICU for “sepsis” and
“acute renal failure.”
• Does the patient have acute renal failure?
– Absolutely! 1.5 x 0.8 = 1.2
• What’s the BUN/Cr ratio?
= Intrarenal
– 32/3.8 = 8.42
• Does the urinalysis help?
– Epithelial cell casts and large proteinuria
consistent with ATN
☻Query opportunity for ARF due to ATN (POA)
potentially giving case an MCC
Example #2
• 87 yo WM w/ Alzheimer’s dementia, CHF, CAD, &
PVD sent to ED from NH for lethargy &
unresponsiveness. Initial workup reveals Na+
= 167, Cl- = 118, K+ = 5.5, BUN = 89, Cr = 2.8.
Lowest recorded BUN & Cr = 29 & 2.1 at recent
discharge for diastolic CHF exacerbation 6 weeks
earlier. CBC essentially WNL while had always been
anemic during previous admissions. Urinalysis
significant for numerous hyaline casts. Patient
aggressively hydrated and BUN & Cr return to his
baseline. Patient eventually discharged to a
different nursing home.
Example #2
• Patient initially admitted for “acute renal failure.”
• Does the patient have acute renal failure?
– NO! 2.1 + 1.0 = 3.1
• What’s the BUN/Cr ratio?
= Prerenal
– 89/2.8 = 31.79
• Does the urinalysis help?
– Hyaline casts consistent with prerenal cause
☻Clarification opportunity for ARI on CKD stage 4
possibly preventing an incorrect coding
submission of ARF
Example #3
• 63 yo WM comes to ED for painful urination,
difficulty initiating stream, hematuria, weakness, & 4
months wt. loss w/out effort. Not seen physician
since 1976. CT scan of urinary tract reveals bilateral
hydronephrosis w/ markedly enlarged & necroticappearing prostate w/ pelvic lymphadenopathy.
Initial BUN & Cr noted to be 55 & 3.3. Foley
catheter insertion results in significant diuresis &
eventual normalization of BUN & Cr. UA WNL
except for hematuria. After biopsy, principal
diagnosis established as “metastatic prostate
cancer” & radical prostatectomy is performed.
Example #3
• Primary service repeatedly documents
“obstructive uropathy” to describe renal function.
• Does the patient have acute renal failure?
– Absolutely! BUN & Cr normalized
• What’s the BUN/Cr ratio?
= Post-renal
– 55/3.3 = 15.71
• Does the urinalysis help?
– Hematuria only not much help
☻Query opportunity for acute renal failure (POA)
potentially giving case a CC
Example #4
• 27 yo AA male comes to ED complaining of hard &
painful inguinal lesions, recurrent fevers w/ chills,
weakness, & fatigue. Initial VS reveal BP = 88/45,
HR = 113, T = 101.9, RR = 28, RA O2 sat = 98%.
Initial BUN & Cr = 31 & 1.4, which improve to 21 &
1.1 w/ hydration. Patient diagnosed w/ sepsis &
requires several abscess I&D procedures. Blood
cxs & abscess cxs repeatedly grow streptococcal
species despite broad spectrum ABX. On hospital
day 9, BUN & Cr start to rise. By day 13, BUN & Cr
= 34 & 4.3 despite aggressive IVF & numerous
medication adjustments.
Example #4
• Does the patient have acute renal failure?
– Absolutely! 1.1 x 1.5 = 1.65
• What’s the BUN/Cr ratio?
– 34/4.3 = 7.9
= Intrarenal
• Is the urinalysis helpful?
– Proteinuria consistent w/ intrarenal pathology
• ASO titer returns positive & renal biopsy reveals
postinfectious glomerulonephritis
☻Query opportunity for ARF & acute poststreptococcal glomerulonephritis (POA)
potentially giving case 1 CC & 1 MCC
Example #5
• 67 yo WM comes to ED w/ complaints of SOB,
swelling, & weakness. Neighbor found him after
being in shower for 6 hours because too weak
to get out. Patient has severe anasarca w/ BUN
& Cr of 94 & 2.9. UA w/ 3–5 hyaline casts. CXR
shows pulmonary edema & ECHO reveals EF ~
15% w/ global hypokinesis. CHF medication
optimization & aggressive IV diuretic regimen do
not produce significant urine output. Natricor &
Bumex drip finally produce results. Patient also
hypotensive throughout hospitalization. Patient
goes home w/ BUN & Cr down to 53 & 1.7.
Example #5
• Patient initially admitted for “anasarca” only.
• Does the patient have acute renal failure?
– Absolutely! 1.7 x 1.5 = 2.55
• What’s the BUN/Cr ratio?
– 94/2.9 = 32.4
= Prerenal
• Does the urinalysis help?
– Hyaline casts consistent with prerenal cause
☻Query opportunities for establishing acute
systolic CHF exacerbation (POA) as principal
diagnosis and for ARF & cardiogenic shock
potentially giving case 1 CC & 1 MCC
Questions?
In order to receive your continuing education certificate for
this program, you must complete the online evaluation which
can be found in the continuing education section at the front
of the workbook.