Precautions

Reliable electrolyte measurements depend on careful technique

Specimen Collection

Patient Preparation
- Fasting: Some electrolyte tests require fasting to minimize interferences from lipemia
- Medications: Certain drugs can affect electrolyte levels. Review the patient’s medication list
- Hydration Status: Assess hydration, as dehydration or overhydration can affect electrolyte concentrations
Specimen Type
- Serum is the most common specimen type for electrolyte measurements
- Plasma may be used for some electrolyte assays, but follow the laboratory’s guidelines for anticoagulant selection
- Whole blood is used for some point-of-care testing (POCT) devices
Tube Type
- Serum separator tubes (SST) or red-top tubes are commonly used for serum collection
- Plasma tubes with lithium heparin are often used for plasma collection
Order of Draw
- Follow the correct order of draw when collecting multiple tubes to prevent cross-contamination
Tourniquet Time
- Minimize tourniquet time (ideally less than 1 minute) to prevent hemoconcentration
Collection Technique
- Use a clean venipuncture technique to minimize hemolysis. Avoid prolonged probing or excessive force
- Avoid drawing blood from an arm with an intravenous (IV) line, if possible

Timing
- Process the specimen as soon as possible after collection to prevent changes in electrolyte concentrations due to cellular metabolism
- Analyze potassium levels promptly, as potassium can be released from cells during storage, leading to falsely elevated results
Centrifugation
- Centrifuge the sample according to the manufacturer’s instructions for the specific tube type
- Proper centrifugation ensures complete separation of serum or plasma from cells
Storage
- If analysis is delayed, store the specimen refrigerated (2-8°C) for short-term storage or frozen (-20°C or -70°C) for longer storage
- Aliquot the sample into smaller portions to avoid repeated freeze-thaw cycles, which can affect electrolyte concentrations
Hemolysis
- Avoid hemolysis, as red blood cells contain high concentrations of potassium and phosphate, which can falsely elevate results
- Visually inspect the sample for hemolysis and reject hemolyzed samples
Lipemia
- Lipemia (excess lipids) can interfere with spectrophotometric assays
- Use lipemia clearing techniques (ultracentrifugation, lipid clearing reagents) or consider methods less affected by turbidity
Precipitation
- Be aware of precipitation with calcium and magnesium, which may lead to false results

Reagent Quality
- Use high-quality reagents and store them according to the manufacturer’s instructions
- Check expiration dates and discard expired reagents
Calibration
- Calibrate the instrument regularly using appropriate standards
- Use multiple calibrators to ensure linearity over the entire measurement range
Quality Control (QC)
- Run quality control samples at regular intervals to monitor the accuracy and precision of the assay
- Use both normal and abnormal QC levels to assess performance across the entire range
- Evaluate QC results before releasing patient results
Instrumentation
- Regularly maintain and service the instrument according to the manufacturer’s recommendations
- Ensure the instrument is functioning properly and that all components are in good working order
Method Validation
- Validate new methods before implementation to ensure accuracy, precision, linearity, and other performance characteristics
- Reference ranges may vary depending on the age of the patient

Endogenous
- Lipemia: Causes turbidity, affecting spectrophotometric readings
- Bilirubin: Absorbs light at similar wavelengths, affecting absorbance readings
- Hemoglobin: Released from hemolyzed red blood cells, interfering with enzymatic reactions
- High Protein Concentrations: Can interfere with enzymatic assays by affecting the reaction kinetics or detection system
Exogenous
- Medications: Certain drugs can directly affect electrolyte levels
- Anticoagulants: Some anticoagulants can interfere with enzymatic reactions
- Contaminants: Improperly cleaned glassware or containers can introduce contaminants that affect assay performance
Pseudohyponatremia
- Occurs with marked hyperlipidemia or hyperproteinemia
- Sodium concentration appears lower due to volume displacement
- Direct ISE methods are less susceptible to this interference
Chloride ISE Interference
- Bromide can interfere with chloride ISE methods
- Sweat Contamination: High chloride content

Unexpectedly High Results
- Pre-Analytical:
  - Patient not fasting
  - Prolonged tourniquet time
  - Hemolysis
  - Improper collection tube
- Analytical:
  - Incorrect calibration
  - Reagent deterioration
  - Interfering substances
  - Instrument malfunction
Unexpectedly Low Results
- Pre-Analytical:
  - Improper storage
  - Analyte degradation
- Analytical:
  - Incorrect calibration
  - Reagent deterioration
  - Instrument malfunction
Inconsistent Results
- Check patient preparation
- Review collection and processing procedures
- Evaluate reagent quality and calibration
- Consider interfering substances
- Repeat the test using a different method or on a new sample
Out-of-Control QC
- Check the integrity of the QC materials
- Prepare fresh QC materials
- Re-calibrate the instrument
- Review reagent quality
- Repeat the QC testing
- If the problem persists, contact the instrument manufacturer for assistance
Lipemia: Can cause an electrolyte imbalance or a false interference. Correct by either using direct ISEs or by clearing the lipemia
Icterus: Can cause interference, so ensure testing reagents are correct and appropriate for testing interferences
Hemolysis: Can release the electrolytic components from within the cell, skewing the results if precautions are not taken

Pre-analytical: Processes that occur before the sample is analyzed
Analytical: Processes involved in analyzing the sample
Interfering Substance: A substance that affects the accuracy of a test
Hemolysis: The breakdown of red blood cells
Lipemia: The presence of excess lipids in the blood
Calibration: Adjusting an instrument to ensure accurate readings
Quality Control: Samples used to monitor the accuracy and precision of a test
SST: Serum Separator Tube
EDTA: Ethylenediaminetetraacetic acid, an anticoagulant
SOP: Standard Operating Procedure
Accuracy: How close a measurement is to the true value
Precision: Reproducibility of a measurement
ISE: Ion-Selective Electrode
POCT: Point of Care Testing