Alpha-HBDH (hydroxybutyrate dehydrogenase) in cats and dogs

Alpha-HBDH is not a separate organ test but part of lactate dehydrogenase (LDH) activity — the “heart-type” forms of LDH found mainly in heart muscle and red blood cells. Much of what is written about it comes from human medicine, where it has largely been replaced by better tests. Hemolysis raises it strongly.

SectionBiochemistry

SampleBlood (serum or plasma), free of hemolysis

UnitsU/L

On formsα-HBDH, HBDH, a-HBDH

What it shows

LDH exists in five forms, LDH1 to LDH5. In small animals LDH1 is found mostly in heart muscle and red blood cells, while LDH5 is found in skeletal muscle and the liver; the middle forms occur in all tissues. In human medicine alpha-HBDH is described as a group of tissue-specific LDH forms found mainly in heart muscle, red blood cells and kidneys, so it is a narrower slice of the same enzyme.

Some labs report the ratio of alpha-HBDH to total LDH, which can hint at whether the source is heart or skeletal muscle. Despite the similar name, this test has nothing to do with beta-hydroxybutyrate, the ketone body measured in diabetes.

Higher than reference — what it may be a sign of

Hemolysis — red cells are rich in these forms of LDH. Destruction of red cells, in the tube or in the body, raises the result. This is the first thing to exclude.
Heart muscle injury — in human medicine alpha-HBDH used to support a suspected heart attack; there it has given way to troponin. In dogs, an older study compared the alpha-HBDH-to-LDH ratio with other ways of telling heart-derived from liver-derived LDH and found another method discriminated better.
Other tissue injury — because the middle LDH forms are everywhere, an increase is never specific to one organ.

Lower than reference

Sources do not describe a clinical meaning of a low alpha-HBDH in cats or dogs. A result below the interval is usually read simply as no sign of increased release.

Look at together with

LDH — the total enzyme; alpha-HBDH is read against it.
Hemolysis index — a hemolyzed sample can explain the whole increase.
CK — the standard enzyme for muscle injury.
Troponin — a dedicated marker of heart muscle injury.

Units and conversion

Alpha-HBDH is reported as enzyme activity in U/L, like LDH. The alpha-HBDH-to-LDH ratio is one U/L value divided by another, so it has no unit. Methods differ, and results from different labs are compared with each lab’s own interval.

Reference range

The reference range is on your lab’s form. Not every lab has an interval for each species. If the form has no interval for your animal, the vet interprets alpha-HBDH together with LDH, CK and the hemolysis index rather than on its own.

Cats and dogs

Cats

In cats, as in dogs, LDH1 sits mostly in heart muscle and red cells, and red cells are rich in LDH, so hemolysis strongly affects the result. Some cats with liver injury have high LDH while CK is normal and the sample is not hemolyzed; liver LDH in small animals is the LDH5 form, not the heart type. Data specific to alpha-HBDH in cats are scarce.

Dogs

For total LDH, serum gives higher values than plasma because cells release the enzyme during clotting — a common artifact in dogs. In chilled or frozen canine serum total LDH stays stable for 4 weeks. In dogs, as in cats, LDH and its forms are non-specific, so CK for muscle and ALT for the liver are usually more informative.

In the app

Add a lab form — Pet Tracker Space recognises the lines, keeps the form’s units and draws each indicator over time with your lab’s reference band.

Open the app

Sources

This page explains what a lab value means. It is not a diagnosis and not a substitute for your veterinarian — only they can interpret results for your pet.