Disadvantages of Photo-Optical Coagulation Instruments
The greatest disadvantage of photo-optical coagulation instruments is interference from lipemia, hemolysis, and hyperbilirubinemia (answer B). 1, 2, 3
How Photo-Optical Coagulation Instruments Work
Photo-optical coagulation instruments measure changes in light transmittance or absorbance during clot formation. These instruments fall into two main categories:
- Transmittance-based systems (e.g., MDA-II, CS series) where transmittance decreases after clot initiation
- Absorbance-based systems (e.g., ACL series) where absorbance increases after clot initiation 4
Major Disadvantages of Photo-Optical Systems
1. Interference from Specimen Characteristics (Primary Disadvantage)
Photo-optical systems are significantly affected by:
Hemolysis: Interferes through both analytical and biological mechanisms:
- High absorbance of cell-free hemoglobin at measurement wavelengths
- Release of tissue factor, proteases, phospholipids, and ADP that can spuriously activate coagulation
- Can affect PT and aPTT results at hemoglobin levels as low as 5 g/L and 1.5 g/L, respectively 2
Hyperbilirubinemia (Icterus):
Lipemia:
These interferences often necessitate additional processing steps like ultracentrifugation or lipid extraction, which adds complexity and time to testing 6.
2. Other Disadvantages
Variability: Coefficients of variance ranging from 7.1% to 39.9% for TEG parameters and 7.0% to 83.6% for ROTEM parameters 4
Hematocrit influence: Variable hematocrit can hinder accurate interpretation in anemic patients 4
Lack of standardization: Different devices produce results that are not interchangeable 4
User dependency: Requires trained personnel and proper calibration 4
Comparison with Other Potential Disadvantages
Availability (Answer A)
While availability was once limited, photo-optical coagulation instruments are now widely available in clinical settings. The Association of Anaesthetists guidelines note their common availability in various forms (TEG, ROTEM, Sonoclot, Quantra, ClotPro) 4.
Complexity of Operation (Answer C)
Although these instruments require trained users, modern systems have improved user interfaces. The complexity is manageable with proper training and is not considered the greatest disadvantage 4.
High Cost (Answer D)
While these instruments have significant upfront costs, the clinical benefits often justify the expense, particularly in high-risk settings like cardiac surgery where they can reduce transfusion requirements 4.
Clinical Implications
The interference from hemolysis, icterus, and lipemia has significant clinical implications:
- May lead to inaccurate results and inappropriate clinical decisions
- Requires additional sample processing or rejection of samples
- Can delay critical coagulation testing in emergency situations
Mitigation Strategies
To minimize interference effects:
- Use readings at wavelengths of 650 nm or above
- Apply higher dilutions of test samples
- Employ high-speed microcentrifugation for lipemic samples
- Consider lipid extraction with organic solvents or lipid-clearing agents for severely lipemic samples 1
The significant impact of these interferences on test accuracy, combined with the need for additional processing steps, makes interference from hemolysis, icterus, and lipemia the greatest disadvantage of photo-optical coagulation instruments.