3-Hydroxybutyrate (beta-hydroxybutyrate)

Main ketone body. Raised in ketosis (fasting, ketogenic diet) or ketoacidosis (diabetes). The value shows how many ketone bodies the liver is currently making from fatty acids.

What 3-hydroxybutyrate does in the body

When insulin falls – during fasting, with few carbohydrates or during prolonged exertion – fat tissue releases fatty acids. The liver takes them up, moves them into its mitochondria with the help of carnitine and breaks them down into acetyl-CoA in beta-oxidation. When more acetyl-CoA is produced there than the citric acid cycle can take up, the liver links the molecules via HMG-CoA into acetoacetate and converts most of it into 3-hydroxybutyrate. The liver itself cannot use ketone bodies and releases them into the blood. The heart, muscles, kidneys and – after a few days of fasting, on a large scale – the brain convert 3-hydroxybutyrate back into acetyl-CoA in their mitochondria and obtain energy from it.

Low 3-hydroxybutyrate – what does it mean?

A low value is the normal case with regular, carbohydrate-containing meals: insulin keeps fat release low, the liver makes hardly any ketone bodies, and the cells meet their needs mainly from glucose. Even during a fasting phase the value can still be low if the switch to using fat has only just begun. Rarely, ketone body production fails to occur despite a longer break from food – this occurs with inherited disorders of fatty acid breakdown or carnitine transport; blood sugar can then fall sharply during fasting.

High 3-hydroxybutyrate – what happens in the body?

A raised value shows that the liver is converting many fatty acids into ketone bodies. During fasting, on a ketogenic diet and after long endurance exercise this is a regulated switch: a residual amount of insulin limits fat release, and the heart, muscles and brain continuously use up the ketone bodies. When insulin is largely absent, by contrast – for example with untreated or poorly controlled type 1 diabetes – fat release and ketone body production run unchecked. The acids then exceed the buffering capacity of the blood, and ketoacidosis develops with intense thirst, nausea, abdominal pain, deep breathing and drowsiness – that is an emergency. In pregnancy, ketone bodies rise faster than usual during longer breaks between meals.

The interpretation is given in your report.