iSTAT Point-of-Care Testing Parameters
The iSTAT analyzer measures blood gases (pH, pCO2, pO2), electrolytes (sodium, potassium, chloride, ionized calcium), metabolites (glucose, lactate, urea, creatinine), and hematocrit using single-use cartridges with 65-100 microliters of blood 1, 2.
Core Parameters Available
The specific parameters depend on which cartridge type is used:
Most Common Cartridge Configurations:
- EC8+ cartridge: Measures sodium, potassium, chloride, urea, glucose, pH, pO2, and pCO2 2
- EC6+ cartridge: Measures sodium, potassium, ionized calcium, glucose, hematocrit, and pH 2
- G3+ cartridge: Measures pH, pO2, and pCO2 (blood gases only) 2
- EG7+ cartridge: Measures pH, pO2, pCO2, sodium, potassium, ionized calcium, and hematocrit 3
- Creatinine cartridge: Available as separate measurement 2
Additional parameters measured include lactate and total hemoglobin (tHb) on certain cartridge types 4.
Performance Characteristics
The iSTAT demonstrates good analytical performance for most parameters in critically ill patients, with important caveats for specific measurements 1.
Accuracy by Parameter:
- Excellent precision (CV <2%): Electrolytes, glucose, urea, and pH 2
- Satisfactory precision (CV <6.5%): Blood gases and creatinine 2
- Poor precision (CV ~21%): Hematocrit 2
Critical Limitations to Know:
High pO2 values (>10 kPa or ~75 mmHg) show significant deviation from laboratory analyzers and should not be relied upon for clinical decisions in hyperoxic patients 1. The linear trend in deviation becomes problematic when pO2 is between 10-30 kPa (r = -0.59 to -0.61, p <0.001) 1.
Hematocrit measurements can underestimate by up to 2.2% in patients with values below 25%, particularly in non-cardiac ICU populations 1. This discrepancy requires awareness when managing anemic patients.
Creatinine measurements in neonatal blood samples have shown clinically significant discrepancies that can affect management decisions 2. Some institutions have discontinued using the iSTAT creatinine assay for this population.
Pre-analytical Considerations
The device shows significant interference from:
- Hemolysis: Affects electrolyte measurements (user is notified by flag) 4
- Benzalkonium: Affects electrolyte measurements (user is notified by flag) 4
No interference occurs from lipemia or methylene blue on co-oximetry results 4.
Clinical Context
Blood gas analyzers like the iSTAT were originally validated in critical care settings for glycemic control protocols 5. The device requires only 2 minutes for analysis and minimal maintenance (2-minute daily electronics check) 6, making it suitable for point-of-care use in critical care units, emergency departments, and operating rooms.
The accuracy established in one patient population cannot be automatically extrapolated to other populations 1, which is why separate validation is essential when implementing iSTAT in different clinical settings (cardiac surgery vs. medical ICU vs. neonatal populations).