A vitreous aspirate has been collected in an emergency at 9 pm. Which of the following is the most appropriate requisite for overnight storage of the sample?
First, the core concept here is the preservation of ocular samples. Vitreous humor is used for diagnosing intraocular infections, like endophthalmitis. The sample needs to be handled properly to prevent degradation of pathogens or contaminants.
The correct answer likely involves refrigeration or specific media. Let's think: if the sample can't be processed immediately, it should be kept in a way that maintains the viability of potential pathogens. Refrigeration at 4°C slows bacterial growth but might not kill them. Alternatively, some sources suggest room temperature with specific transport media.
Wait, but for vitreous aspirates, the standard is to refrigerate them. Let me confirm. In ophthalmology, vitreous samples for culture are typically stored at 4°C if not processed immediately. This prevents overgrowth of contaminants and preserves the organisms. So the correct answer would be refrigeration at 4°C.
Now, the wrong options might be things like leaving at room temperature, freezing, or using inappropriate media. For example, room temperature might allow bacterial growth, while freezing could damage cells. Transport media might not be suitable if the sample is not in the right container.
Clinical pearl: Remember that vitreous samples for culture should be refrigerated to maintain pathogen viability and prevent contamination. Also, note that some labs might have specific protocols, but the general rule is refrigeration.
**Core Concept**
The vitreous humor is a sterile, gel-like substance in the posterior segment of the eye. When collected for diagnostic purposes (e.g., endophthalmitis), proper storage preserves microbial viability and prevents degradation of analytes like glucose or PCR targets. Key principles include avoiding temperature extremes that kill pathogens, prevent contamination, and maintain sample integrity.
**Why the Correct Answer is Right**
Refrigeration at 2–8°C (4°C) is the standard for overnight storage of vitreous aspirates. This slows bacterial and fungal growth without killing potential pathogens, preserves enzyme activity (e.g., lactate dehydrogenase), and maintains glucose levels for accurate interpretation. It also prevents protein denaturation and cellular degradation, ensuring reliable culture and PCR results.
**Why Each Wrong Option is Incorrect**
**Option A:** Room temperature (20–25°C) accelerates microbial overgrowth and contaminant proliferation, compromising diagnostic accuracy.
**Option B:** Freezing (<0°C) causes ice crystal formation, lysing cells and degrading analytes like glucose and nucleic acids.
**Option C:** Incubation at 37°C promotes rapid growth of contaminants and non-pathogens, masking true pathogens.
**Clinical Pearl / High-Yield Fact**
Always refrigerate vitreous aspirates if processing is delayed. A classic exam trap is confusing vitreous storage with blood or CSF, which have different requirements. For endophthalmitis, time-sensitive analysis (e.g., PCR) may require immediate processing, but refrigeration is the safest default.
**Correct Answer: C. Refrigeration at 4°C**