Can Quantab titrator sticks reliably predict urinary sodium?

Area of Science:

• Clinical Chemistry
• Point-of-Care Testing
• Diagnostic Accuracy

Background:

• Urinary sodium concentration is a key indicator of extracellular fluid depletion and dehydration.
• Current laboratory assessment of urinary sodium can cause delays in clinical decision-making.
• Point-of-care (POC) testing for urinary sodium could expedite fluid and salt management.

Purpose of the Study:

• To compare laboratory-assessed urinary sodium with a POC urinary chloride test.
• To evaluate the utility of urinary chloride as an indicator of low urinary sodium (<20 mmol/L).
• To determine the optimal cut-point for a urinary chloride POC test.

Main Methods:

• Urinary chloride was measured using a Quantab titrator stick on 127 patient samples.
• Laboratory-assessed urinary sodium concentrations were used for validation.
• Correlation coefficients and limits of agreement were calculated.
• Sensitivity and specificity were used to find the optimal cut-point for low urinary sodium.

Main Results:

• Twenty-three percent of samples had low urinary sodium (<20 mmol/L).
• A Quantab scale threshold of <4.3 demonstrated a 56% positive predictive value for low sodium.
• The negative predictive value for low sodium was 94% at this threshold.

Conclusions:

• The Quantab stick shows potential as a POC test for aiding fluid and salt management decisions.
• This test may be particularly useful in outpatient settings.
• Further research is warranted in specific patient populations at risk of dehydration.