Posting this under the heading it deserves: Second pass at: Gauge and length selection for subcutaneous injection Everything below is what sits behind that.
The question about Gauge and length selection that I actually want answered is the second one below. The first is context and I have kept it short.
Both are stated with units, and I have said what I already checked so that nobody repeats it.
Gauge is the outside diameter and higher numbers are thinner. Thinner needles hurt less and draw more slowly, which is the entire trade.
I looked this up rather than remembered it, which is the right order.
Post #2 describes the usual case. This is about the unusual one.
Needle length: typical lengths for subcutaneous injection are 4-6 mm (short), 8 mm (standard), or 10-12 mm (longer). Longer needles are needed for deeper tissue or if you have abdominal adiposity.
That is what I would do. It may not be what is correct.
Aspirating before injection: for subcutaneous injection, aspirating (pulling back on the plunger to check for blood) is not necessary and is sometimes discouraged because it is associated with more discomfort. Subcutaneous injection without aspiration is standard practice.
That has held every time I have looked, which is not the same as always.
Reporting rather than recommending, on Gauge and length selection. What happened is above. Whether it should have is a different question and not one I am qualified to answer.
The arithmetic in post #4 is right; the assumption feeding it is the part to check.
Sharps containers are a legal requirement for disposal in several jurisdictions and a sensible precaution everywhere. A rigid sealed container is the minimum.
Take the reasoning and check the arithmetic; I do not always get it right.
Answering the question post #6 raises rather than the one it answers.
Counterpoint on Gauge and length selection, offered without confidence: the same observation is consistent with a much duller explanation, and nobody has ruled the dull one out.
Post #6 put the caveat in the right place and I want to underline it.
Needle gauge: smaller numbers (30G) are finer and less painful. Larger numbers (25G) are courser. For subcutaneous injection, 27-30G is typical. Finer needles take longer to draw up but hurt less.
That reframing is the whole thing. The facts I already had.
Where I part company with post #12, and it is a narrow parting.
Speaking only to Gauge and length selection as I have actually seen it, rather than as it is usually described: the effect is real, it is smaller than the thread suggests, and the variance between people is larger than the effect.
Reusing a needle blunts it and there is no benefit to offset that. The second injection with the same needle is the one people describe as painful.
Narrowing post #13, because the general version has more than one answer.
The most useful thing anyone has posted about Gauge and length selection in this category was a table of what had been measured and by whom. That is what I would want again.
Two claims get bundled together under Gauge and length selection and they need separating. The descriptive one — this is what was observed — is usually well supported. The causal one — this is why — usually is not.
Almost every disagreement in threads like this one dissolves once you say which of the two you are making.
U-100 means the barrel is graduated for a solution containing one hundred units of insulin per millilitre. For anything that is not insulin, the units are simply hundredths of a millilitre.
Everything in post #20 holds. The case it does not cover is the one I have.
Adding a reference point for Gauge and length selection. Mine is a single case, collected without controls, and I am posting the method alongside it so it can be discounted appropriately.
Reading rather than answering, but this is the post I would point somebody at.
U-100 means the barrel is graduated for a solution containing one hundred units of insulin per millilitre. For anything that is not insulin, the units are simply hundredths of a millilitre.
One of those cases where knowing the mechanism does not help the decision.
Narrowing post #22, because the general version has more than one answer.
Two people in this thread mean different things by Gauge and length selection and are disagreeing about the definition while believing they are disagreeing about the facts. Worth pausing to define it.
Everything in post #24 holds. The case it does not cover is the one I have.
The version of Gauge and length selection that circulates here is a simplification of a simplification. It is not wrong, but it has lost the conditions under which it holds, and those conditions are where the interesting cases live.
Practical answer on Gauge and length selection, since the theoretical one is upthread: do the simplest check first, write down the result, and only then decide whether the complicated explanation is needed. It usually is not.
Adding the measurement that post #26 says would settle it.
Since Gauge and length selection keeps coming up, it should probably be a maintained page rather than a recurring thread. I am happy to draft it if someone with more direct experience will review it.