Pancreas

The two halves are not as separate as they look

They share a blood supply, and the direction it runs in has a consequence. Blood reaches the islets first and then drains onward through the capillaries of the surrounding enzyme-producing tissue. That tissue is therefore bathed in insulin at concentrations many times higher than anything reaching the rest of the body.

Insulin is a growth and activation signal for those cells, so the arrangement appears to exist to keep them working. It also means that when the islets fail, the enzyme-producing half loses a signal it has always had. That is part of why reduced digestive enzyme output is more common in long-standing diabetes than the 2 conditions being unrelated would suggest.

How the gland avoids digesting itself

This is the mechanism that explains what pancreatitis actually is, and why a lipase result means what it does.

The pancreas manufactures enzymes capable of dissolving protein, fat and starch, inside cells made of exactly those materials. It survives this through several layers of protection. The protein-digesting enzymes are made as inactive precursors, folded so the working part is blocked. They are packaged into sealed granules. Inhibitor proteins sit inside those granules ready to neutralise anything that activates early. And the switch that turns the lead enzyme on is not in the pancreas at all. It sits in the lining of the small intestine, so activation is meant to happen only after the enzymes have left.

Acute pancreatitis is what happens when that fails and the enzymes activate while still inside the gland. The organ begins digesting itself, and the contents of the damaged cells spill into the bloodstream. That is the rise a lipase test detects.

Lipase is a partial exception. Unlike the protein-digesting enzymes it is secreted already active, because a fat-digesting enzyme poses no threat to a cell built of protein. What it cannot do alone is work on a fat droplet in the presence of bile salts, which coat the surface and keep it off. It needs a small partner protein to anchor it there, and that partner is released as an inactive precursor, switched on by the same intestinal activation step. So the control is still there. It has just been moved one step sideways.

What the profile looks at

Lipase belongs in the gut rather than in the bloodstream, and only small amounts leak into blood normally. It rises sharply when the gland is inflamed and its cells are damaged. It has largely replaced amylase as the first-line test because amylase also comes from the salivary glands and from other abdominal organs, and because lipase stays raised for days longer, which matters for anyone who is seen late rather than on the first day.

What a lipase result can and cannot answer

This is the marker on our menu whose threshold most clearly belongs to someone who is unwell rather than to someone who is checking.

Acute pancreatitis is diagnosed internationally by the revised Atlanta classification, which requires 2 of 3 things: characteristic upper abdominal pain, usually radiating through to the back; a lipase or amylase at least 3 times the upper limit of the lab's own reference range; and characteristic findings on a scan. The number is one leg of a tripod. It was never meant to stand on its own.

And it is a threshold built around a person in pain. Labs do publish a reference range built from people who feel fine, but no threshold inside that range has been shown to mean anything in someone with no symptoms. A lipase that stays raised in a well person is often chronic asymptomatic pancreatic hyperenzymaemia, also called Gullo's syndrome, which is classed as harmless after the pancreas has been imaged and found normal.

So a normal lipase in a well person tells you the pancreas is not acutely inflamed today. It does not tell you the organ is healthy, it does not assess how well it produces digestive enzymes over time, and it says nothing whatever about the insulin-producing half.

That is a narrow thing to be able to say, and it is all this marker says.

What changes when the pancreas is under strain

Acute inflammation is sudden and unmistakable, and it is a hospital problem rather than a testing one. Gallstones and alcohol are the two most common causes, with very high triglycerides a distant third. This is why severely raised triglycerides are treated as an urgent problem, and why the concern at that level is the pancreas rather than the arteries.

Longer-running damage is quieter and does not show up on this marker at all. Gradual loss of enzyme production presents as fatty, pale, hard-to-flush stools and weight loss despite eating normally. The test for it is faecal elastase, which measures how much of one pancreatic enzyme survives into a stool sample. One sample, no preparation, a GP can arrange it and private labs sell it. A normal result rules enzyme loss out reasonably well. A low result is weaker evidence, since mild loss is often missed and a low reading in someone unlikely to have it often turns out to be a false alarm, so it is confirmed rather than acted on alone. And if it is low there is a treatment, which is taking the enzymes as capsules with meals. Damage to the islets presents as diabetes, and is picked up by the markers in the section above instead.