IL-6 in the cell supernatant is very low. Which company's mouse IL-6 ELISA kit has sufficient sensitivity?

Recently, imported items in stock generally take 1-2 weeks, while transfer plus customs clearance and cold chain may take 4-6 weeks or even longer, so it is indeed unstable. You can ask two agents at the same time to confirm whether it is domestic stock or needs to be ordered from the manufacturer. If you cannot wait, you can first use a domestic high-sensitivity kit as a transition, or use 50 µL samples for single wells or a small number of replicate wells for initial screening. After receiving the goods, do not directly test precious samples. First measure the standard curve, blank, and low-value spike. If the low points cannot be separated or the blank is high, contact them promptly for return or exchange.

50 µL is a hard requirement. It is recommended to directly ask technical support whether samples can be loaded as "50 µL sample + 50 µL diluent," or whether the diluent can be reduced. If the sample volume is limited, do not blindly perform multiple dilutions; prioritize neat sample or 1:2. Use low-level spike recovery to determine the actual lower limit of quantification: spike the matrix at 2, 5, and 10 pg/mL and check whether the recovery falls within the acceptable range, rather than relying solely on standard curve linearity. Only if the recovery at 2 pg/mL spike is stable can you have confidence in reporting low values; otherwise, ND may be due to the method itself not being able to go that low.

Prioritize R&D Systems' Quantikine HS or BioLegend's ELISA MAX Deluxe/high-sensitivity series; these tend to be relatively stable on low-value samples, and the lowest standard curve point can usually approach 2 pg/mL. However, don't just look at the LoD in the instructions—confirm the lowest standard curve point and sample loading volume. Many high-sensitivity kits require 100 µL, which consumes sample. I previously also got quite a few ND results with domestic kits, but after switching to high-sensitivity ones, low values could be distinguished. Ask the agent to provide the latest COA and standard curve template, and it's best to verify it yourself with 2, 5, and 10 pg/mL spike recovery.

If you lock in the imported high-sensitivity series within 3000, after tax and cold-chain shipping it may just hit the line or slightly exceed it, especially since spot prices and transfer prices differ. Domestic high-sensitivity series such as Lianke and Xinbosheng usually have more favorable unit prices, but sensitivity must be validated with your low-value samples. It is recommended to first obtain a small size or apply for trial samples and run a batch of low-value samples; do not buy in bulk the first time. When requesting a quote, ask clearly whether tax is included, whether cold-chain door-to-door delivery is included, lead time, shelf life, and return/exchange conditions. Some low prices may include only ordinary ice packs and not temperature records.