Hyperkalemia diagnostic study of choice

Hyperkalemia Microchapters
Home
Patient information
Overview
Historical Perspective
Classification
Pathophysiology
Causes
Differentiating Hyperkalemia from other Diseases
Epidemiology and Demographics
Risk Factors
Screening
Natural history, Complications and Prognosis
Diagnosis
Diagnostic Study of Choice
History and Symptoms
Physical Examination
Laboratory Findings
Electrocardiogram
X-ray
Echocardiography and Ultrasound
CT scan
MRI
Other Imaging Findings
Other Diagnostic Studies
Treatment
Medical Therapy
Surgery
Primary Prevention
Secondary Prevention
Cost-Effectiveness of Therapy
Future or Investigational Therapies
Case Studies
Case #1
Hyperkalemia diagnostic study of choice On the Web
Most recent articles
Most cited articles
Review articles
CME Programs
Powerpoint slides
Images
American Roentgen Ray Society Images of Hyperkalemia diagnostic study of choice All Images X-rays Echo & Ultrasound CT Images MRI
Ongoing Trials at Clinical Trials.gov
US National Guidelines Clearinghouse
NICE Guidance
FDA on Hyperkalemia diagnostic study of choice
CDC on Hyperkalemia diagnostic study of choice
Hyperkalemia diagnostic study of choice in the news
Blogs on Hyperkalemia diagnostic study of choice
Directions to Hospitals Treating Hyperkalemia
Risk calculators and risk factors for Hyperkalemia diagnostic study of choice

Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief:

Diagnostic Study of Choice

Study of choice

[Serum potassium] is the gold standard test for the diagnosis of [hyperkalemia].

There are two methods to determine serum potassium   :

• Flame emission spectrophotometry

• Ion-specific electrode (ISE) potentiometry

ISE potentiometry has two different subtypes: Direct (undiluted) and indirect (diluted).

Direct ISE measures plasma potassium directly from a whole-blood sample and it's not associated with either pseudohyperkalemia.

FES or indirect ISE requires sample dilution before assay and both are associated with pseudohyperkalemia.

Pseudohyperkalemia

Pseudohyperkalemia is defined when serum potassium concentration exceeds that of plasma without any symptoms of hyperkalemia.It usually occurs when potassium moves out of cells during blood specimen collection or during centrifugation of the sample.Other causes are thrombocytosis,leukocytosis and erythrocytosis.To rule out pseudohyperkalemia we need to do the following

*Repeat the blood sample

*Complete blood count to rule out thrombocytosis,erythrocytosis and leukocytosis

*Measurement of plasma potassium and whole blood potassium

Diagnostic results

The finding on performing the diagnostic test that confirms hyperkalemia

*Serum Potassium level more than 5.1 meq/L.

Common Diagnostic Studies

The [serum potassium] must be performed when:

• The patient presented with cardiac arrhythmias,weakness,fatigue and known case of chronic kidney disease as the first step of diagnosis.

The various investigations must be performed :

• Blood pressure(to look for hypoaldosteronism)
• Complete blood count
• Renal function tests
• Urine potassium,sodium and osmolality
• Metabolic profile(other electrolytes)
• ECG
• Bicarbonate level
• Serum glucose
• Serum Calcium

Depending on the history and results of the above mentioned tests,other tests that can be performed for evaluating the cause of hyperkalemia.

• Digoxin level - If the patient is on a digitalis medication
• Arterial or venous blood gas
• Urinalysis
• Serum cortisol and aldosterone levels
• Serum uric acid and phosphorus assays
• Serum creatinine phosphokinase (CPK) measurements
• Urine myoglobin test

Sequence

• Serum Potassium measurement

• ECG-It denotes the urgency of the treatment

• Renal function test

Serum BUN and creatinine are measured.

Since creatinine levels are dependent on muscle mass so GFR measurement is preferred

• Urine potassium,sodium and osmolality measurement

Urine potassium measurement

Urine potassium <20meq/L denotes impaired excretion of potassium and denotes renal cause of hyperkalemia.

Urine potassium .40meq/L denotes adequate excretion of potassium and excludes renal cause of hyperkalemia.

Urine sodium <20meq/L denotes decreased sodium delivery to the distal tubules which decreases potassium secretion.

Urine osmolarity

measuring urine osmolarity is very important for accurate measurement of urine potassium as concenterated or dilute urine will alter the urine potassium concenteration.

• Serum osmolarity

High serum osmolarity(>295 mosm/kg) may result in extracellular shift of potassium .

• Blood gas analysis

Decreased serum ph causes extracellular shift of potassium into the blood

• Transtubular Potassium gradient

It calculates the ratio of amount potassium in the collecting duct of kidneys with the amount of potassium in the peritubular capillaries.

It indicates the activity of aldosterone on kidneys in regulation of potassium levels.

TTG calculation-( Urine K+ X Serum osmolarity)/(serum K+ X Urine omolarity)

TTG <3 suggests lack of aldosterone effect on collecting ducts causing decreased excretion of potassium.

TTG >7 suggest adequate effect of aldosterone in a case of hyperkalemia.

If TTG suggest aldosterone etiology then further testing done

Aldosterone levels

Renin levels

Diagnostic approach to hyperkalemia

Potassium >5.1meq/L

ECG

If no changes,rule out pseudohyperkalemia

If changes present then start urgent treatment

Urine sodium <25 meq/L

urine sodium >25 meq/L

ARF CKD Heart failure Volume depletion

Decreased K+secretion(Urine K+<20meq/L

Transcellular shift(measure serum osmolarity and pH)

Low aldosterone(TTG<3)

Normal aldosterone(TTG>7)

Diabetic ketoacidosis Metabolic acidosis

Low renin

Normal renin

Tissue breakdown Pseudohypoaldosternism type 1 and type 2 Type 1 RTA

Interstital nephritis Obstructive uropathies Diabetic nephropathy ACE inhibitors,Angiotensin 2 receptors

Primary hypoaldosteronism Congenital adrenal hyperplasia Aldosterone receptor antagonists RTA type 4