eMedicine Specialties > Nephrology > Acute Kidney Failure
Acute Tubular Necrosis: Differential Diagnoses & Workup
Updated: Aug 28, 2009
- Overview
- Differential Diagnoses & Workup
- Treatment & Medication
- Follow-up
- Multimedia
Differential Diagnoses
Acute Renal Failure
Azotemia
Chronic Renal Failure
Glomerulonephritis, Acute
Nephritis, Interstitial
Other Problems to Be Considered
Prerenal azotemia
Acute interstitial nephritis
Renal vasculitis
Obstructive uropathy
Workup
Laboratory Studies
Serum chemistries: By definition, BUN and serum creatinine concentrations are increased in ARF. In addition, hyponatremia, hyperkalemia, hypermagnesemia, hypocalcemia, and hyperphosphatemia may be present. A metabolic acidosis is also found. Remember that hypercalcemia and hyperuricemia may suggest a malignant condition as a cause.
CBC count: CBC count may reveal anemia. Erythropoietin production is decreased in ARF, and dysfunctional platelets (from uremia) also make bleeding more likely.
Urinalysis: The centrifuged sediment of urine is particularly helpful because it may reveal pigmented, muddy brown, granular casts, suggesting that established ATN is present. However, remember that these casts may be absent in 20-30% of patients with ATN. In addition to the routine urinalysis, urine electrolytes may also help differentiate ATN from prerenal azotemia. The urinary sediment, electrolyte, and osmolality findings that can help to separate ATN from prerenal azotemia are illustrated in the following Table.
Laboratory Findings Used to Differentiate Prerenal Azotemia From ATN
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Table
| Finding | Prerenal Azotemia | ATN and/or Intrinsic Renal Disease |
|---|---|---|
| Urine osmolarity (mOsm/kg) | >500 | <350 |
| Urine sodium (mmol/d) | <20 | >40 |
| Fractional excretion of sodium (%) | <1 | > 2 |
| Fractional excretion of urea (%) | <35 | >50 |
| Urine sediment | Bland and/or nonspecific | May show muddy brown granular casts |
| Finding | Prerenal Azotemia | ATN and/or Intrinsic Renal Disease |
|---|---|---|
| Urine osmolarity (mOsm/kg) | >500 | <350 |
| Urine sodium (mmol/d) | <20 | >40 |
| Fractional excretion of sodium (%) | <1 | > 2 |
| Fractional excretion of urea (%) | <35 | >50 |
| Urine sediment | Bland and/or nonspecific | May show muddy brown granular casts |
Fractional excretion of a substance is calculated by the formula (U/P)z/(U/P)Cr X 100, where z is the substance, U and P represent urine and plasma concentrations, and Cr stands for creatinine.
Imaging Studies
- An abdominal radiograph is of limited benefit in ARF, with the exception of diagnosing (or helping to exclude) nephrolithiasis.
- Ultrasonography, computed tomography (CT) scanning, and MRI are extremely useful to exclude obstructive uropathy and to measure renal size and cortical thickness. Renal ultrasonography is a simple procedure that should be undertaken in all patients who present with ARF.
Procedures
- Biopsy is rarely necessary. It should be performed only when the exact renal cause of ARF is unclear and the course is protracted. Prerenal and postrenal causes must be ruled out first. The diagnosis of ATN is made on a clinical basis, that is, with the help of a detailed and accurate history, a thorough physical examination, and pertinent laboratory examinations and imaging studies. A more urgent indication for renal biopsy is in the setting of clinical and urinary findings that suggest renal vasculitis rather than ATN; the diagnosis needs to be established quickly so that appropriate immunomodulatory therapy can be initiated. The biopsy is performed under ultrasound or CT scan guidance after ascertaining the safety of the procedure. A biopsy may also be more critically important in the setting of a renal transplant patient to rule out rejection.17,18
Histologic Findings
In most circumstances, the histology demonstrates the loss of tubular cells or the denuded tubules. As illustrated in the image below and in Image 1, the tubular cells reveal swelling, formation of blebs over the cellular surface, and exfoliation of the tubular cells into the lumina. The earliest finding could be loss of the cellular brush border. (See also images below and Images 2-5.)
A photomicrograph of renal biopsy shows renal medulla, which is composed mainly of renal tubules. Patchy or diffuse denudation of the renal tubular cells is observed, suggesting acute tubular necrosis (ATN) as the cause of acute renal failure (ARF).
Acute tubular necrosis (ATN). Flattening of the renal tubule cells due to tubular dilation.
Acute tubular necrosis. Intratubular cast formation.
Acute tubular necrosis. Intratubular obstruction due to the denuded epithelium and cellular debris. Note that the denuded tubular epithelial cells clump together due to rearrangement of intercellular adhesion molecules (ICAM).
Sloughing of cells, which is responsible for the formation of granular casts, a feature of acute tubular necrosis (ATN).
More on Acute Tubular Necrosis |
| Overview: Acute Tubular Necrosis |
 Differential Diagnoses & Workup: Acute Tubular Necrosis |
| Treatment & Medication: Acute Tubular Necrosis |
| Follow-up: Acute Tubular Necrosis |
| Multimedia: Acute Tubular Necrosis |
| References |
| Further Reading |
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References
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Further Reading
Related eMedicine topics:
Acute Renal Failure
Acute Tubular Necrosis [Pediatrics: General Medicine]
Azotemia
Kidney Transplantation, Surgical Complications
Kidney, Trauma
Oliguria
Renal Failure, Acute
Clinical guidelines:
ACR Appropriateness Criteria® renal failure. American College of Radiology - Medical Specialty Society. 1995 (revised 2005). 8 pages. [NGC Update Pending] NGC:004615
Clinical trials:
Allogeneic Multipotent Stromal Cell Treatment for Acute Kidney Injury Following Cardiac Surgery
Sensitivity and Specificity of NGAL in an Emergency Room Population
Keywords
acute tubular necrosis, renal failure, kidney failure, acute renal failure, tubular necrosis, end-stage renal disease, acute kidney failure, intrinsic renal disease, acute ischemic nephropathy, ischemic acute tubular necrosis, nephrotoxic acute tubular necrosis
