Uremic Encephalopathy Workup

Updated: Oct 28, 2022
  • Author: James W Lohr, MD; Chief Editor: Vecihi Batuman, MD, FASN  more...
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Laboratory Studies

Obtain the following laboratory studies:

  • Kidney function studies [13] – Markedly elevated blood urea nitrogen (BUN) and creatinine levels are seen in uremic encephalopathy

  • Serum electrolyte and glucose measurements – To rule out hyponatremia, hypernatremia, hyperglycemia, and hyperosmolar syndromes as the cause of encephalopathy

  • Complete blood cell count – To detect leukocytosis, which may suggest an infectious cause, and to determine whether anemia is present (anemia may contribute to the severity of mental alterations)

  • Serum calcium, phosphate, and parathyroid hormone (PTH) levels – To assess for hypercalcemia, hypophosphatemia, and severe hyperparathyroidism, which cause metabolic encephalopathy

  • Serum magnesium level – This may be elevated in a patient with renal insufficiency, particularly if the patient is ingesting magnesium-containing antacids; hypermagnesemia may manifest as encephalopathy

  • Toxicology screen

  • Medication levels

Determine drug levels because medications (eg, digoxin, lithium) may accumulate in patients with kidney failure and contribute to encephalopathy. However, some medications that are excreted by the kidney cannot be detected. These may also accumulate in patients with kidney failure, resulting in encephalopathy (eg, penicillin, cimetidine, meperidine, baclofen).


Imaging Studies

Obtain a magnetic resonance imaging (MRI) or computed tomography (CT) scan of the head in uremic patients who present with severe neurologic symptoms, to rule out structural abnormalities (eg, stroke, intracranial mass, subdural hematoma).

Typical MRI findings in patients with uremic encephalopathy include increased signal intensity (lentiform fork sign) in either the cerebral cortex or the basal ganglia. [14, 15] A CT scan may show bilateral hypodensities involving the basal ganglia, midbrain, or thalamus. [16]

In a prospective study of 20 patients diagnosed with uremic encephalopathy, MRI scans did not show basal ganglia findings, and the lentiform fork sign was not observed. However, in the majority of patients the MRI showed white matter involvement and cerebral or cortical atrophy, and in half the patients, arterial blood gas (ABG) analysis revealed metabolic acidosis. The researchers concluded that while the lentiform fork sign and basal ganglia involvement can confirm the diagnosis, uremic encephalopathy cannot be ruled out in its absence; in those cases, clinical manifestations and laboratory findings need to be taken into account. [17]



An electroencephalograpm (EEG) is commonly performed on patients with metabolic encephalopathy. Findings typically include the following:

  • Slowing and loss of alpha frequency waves
  • Disorganization
  • Intermittent bursts of theta and delta waves with slow background activity

Reduction in frequency of EEG waves correlates with the decrease in renal function and the alterations in cerebral function. After the initial period of dialysis, clinical stabilization may occur while the EEG findings do not improve. Eventually, EEG results move toward normal.

Aside from the routine EEG, evoked potentials (EPs) (ie, EEG signals that occur at a reproducible time after the brain receives a sensory stimulus [eg, visual, auditory, somatosensory]) may be helpful in evaluating uremic encephalopathy. Chronic renal failure prolongs latency of the cortical visual-evoked response. Auditory-evoked responses are generally not altered in uremia, but delays in the cortical potential of the somatosensory-evoked response do occur.


Cognitive Function Tests

 Several cognitive function tests are used to evaluate uremic encephalopathy, including the following:

  • Trail-making test – Measures psychomotor speed; uremia may result in worse performance
  • Continuous memory test – Measures short-term recognition
  • Choice reaction time test – Measures simple decision making

Alterations in choice reaction time appear to correlate best with renal failure.



Lumbar puncture is not routinely performed; however, it may be indicated to find other causes of encephalopathy if a patient's mental status does not improve after initiation of dialysis. No specific CSF finding indicates uremic encephalopathy.