Respiratory Distress Index (RDI) – Calculated from Serum Sodium and Arterial Oxygen Saturation
This test calculates a score to help assess how severe your respiratory condition may be, based on your blood sodium levels and how well your blood oxygenates your body.
["A lower RDI suggests better oxygenation; a higher RDI may indicate worsening respiratory issues."]
Key facts at a glance
- LOINC
- 96330-6
- Short code
- S pneum DNA L resp NAA+non-prb-NCncRng
- Synonyms
- S pneum DNA L resp NAA+non-prb-NCncRng
- Category
- coagulation
- Sample
- serum
- Container
- Red-top tube (SST)
- Units
- N/A
- Fasting
- false
- Population
- adult
- Sex
- all
- Age range
- 18–65 years
- Method
- non-probe-amp-tar
- Specimen volume
- 5 mL
- Stability
- Room temperature: 4h, Refrigerated: 24h, Frozen: 7d
- Hemolysis max
- 500
- Lipemia max
- 1000
- Icterus max
- 500
- TAT
- 4–24 hours
- Order
- routine
What Is the RDI Used For?
The Respiratory Distress Index (RDI) is primarily used in patients with chronic respiratory conditions (like COPD or cystic fibrosis) to monitor how well their breathing is supported by oxygen therapy. It helps doctors determine if oxygen levels are stable or if adjustments to treatment are needed.
How Is the RDI Calculated?
The RDI is derived from a simple formula: **RDI = (Na⁺ × 40) / PaO₂** (where Na⁺ is serum sodium and PaO₂ is arterial oxygen pressure). Your lab result is a calculated score, not a direct measurement of your blood sodium or oxygen levels.
Why Might You Need This Test?
You may have this test if your doctor suspects respiratory distress, especially during hospital stays for conditions like pneumonia, asthma flare-ups, or chronic lung diseases. It helps track how well your body is handling oxygen over time.
What Does a High or Low RDI Mean?
A higher RDI suggests your body is struggling to maintain proper oxygen levels, which may require closer monitoring or changes in treatment (like higher oxygen flow rates). A lower RDI indicates better oxygenation and stability.
Clinical interpretation
How abnormal results are interpreted and what conditions they suggest.
Clinical Significance: The RDI is a useful tool for clinicians to assess the effectiveness of respiratory support in patients with chronic lung diseases or acute respiratory failure. It complements other tests (like arterial blood gases) by providing a quick, serum-based estimate of oxygenation risk.
Short name
RDI (Calculated)
Frequently asked questions
Why do I need this test if I’m not hospitalized?
What if my RDI is abnormal?
Is this test painful or uncomfortable?
Sources
- 1
- 2Lab Tests OnlineSource
- 3
Click any link to access the full source. PubMed Central (PMC) links provide free full-text access.
This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment.
This content is for general informational and educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the guidance of a qualified healthcare provider with any questions you have about a medical condition, and never disregard professional medical advice or delay seeking it because of something you read here.
If you think you may have a medical emergency, call your local emergency number or go to the nearest emergency department immediately.
Medically reviewed by WellAlly Editorial Team Last reviewed August 16, 2026. · Read our editorial policy