Other urine crystals (cystine, bilirubin, amorphous, unclassified) in cats and dogs
Besides struvite, calcium oxalate and urates, a urine report may list rarer or less specific crystals. Some, such as amorphous salts, usually mean little; others — cystine in any animal, bilirubin crystals in a cat — are a reason for a closer look. As with all crystals, the finding is read together with how fresh the sample was.
What it shows
This article covers four lines of the form. The main one is the general line for other or unclassified crystals.
- Other / unclassified — crystals that do not fit the usual types: crystals from some medicines or X-ray contrast agents, very rare amino acid crystals, and needle- or plate-shaped crystals reported in dogs whose identity is uncertain.
- Cystine — flat colourless hexagonal plates, often stacked in layers; they form in acidic urine. They indicate cystinuria, an inherited defect in how the kidney tubules reabsorb certain amino acids.
- Bilirubin — yellow needle-like or granular crystals that often settle on other elements; they reflect bilirubin in urine.
- Amorphous salts — fine granular material with no defined shape, made of urates (acidic urine, yellow to yellow-brown), phosphates (neutral or alkaline urine, colourless) or xanthine. They can look like bacteria; a stain helps tell them apart.
Higher than reference — what it may be a sign of
- Cystine — cystinuria. Kidney function is otherwise normal; the main consequence is a tendency to form stones. In a dog, cystine crystals indicate a risk of cystine stones.
- Bilirubin crystals in a cat — abnormal; the vet looks for a cholestatic process, in which bile does not flow normally.
- Bilirubin crystals in a dog — often of no significance, especially in concentrated urine, since healthy dogs can have low but detectable bilirubin in urine.
- Amorphous salts — generally no specific interpretation is possible; they can be seen in healthy animals.
- Crystals from medicines — the vet compares the finding with the medicines the animal gets and any recent contrast X-ray study.
- Unknown crystals — what they mean depends on symptoms and history.
Lower than reference
No such crystals is the usual result. A missing cystine line does not exclude cystinuria: crystals do not form in every supersaturated sample, and stones can be present without visible crystals. For a few breeds a genetic test for cystinuria is available.
Look at together with
- Total bilirubin in blood — together with bilirubin crystals, especially in a cat.
- Urine pH — cystine and amorphous urates form in acidic urine, amorphous phosphates in neutral or alkaline urine.
- Urine specific gravity — bilirubin crystals in dogs are most common in concentrated urine.
- Bacteria in urine — amorphous salts can mimic bacteria.
- Urate crystals — amorphous urates often accompany them.
Units and conversion
These lines have no unit to convert. Cystine and bilirubin may be given as a number or range per high-power field (/hpf) or in words; amorphous salts and other crystals are usually described only in words — “not found”, “few”, “many”.
Reference range
The reference range is on your lab’s form; for these lines there is usually no number. The sample matters as much as the result: crystals of no clinical importance can form in urine that stood or was chilled after collection, so fresh urine matters (see struvite for how storage affects crystals). A cystine crystal or, in a cat, a bilirubin crystal is worth discussing with the vet even if the form shows no flag.
Cats and dogs
The sources describe cystinuria mainly in dogs; in cats Merck lists cystine stones only as less common than other types. In cats any bilirubin crystals — or a positive bilirubin pad on the dipstick — are abnormal and prompt a look for a cholestatic process. Amorphous salts generally carry no specific meaning in cats either.
Cystinuria is reported in many breeds and in mixed-breed dogs; breeds named include, among others, Newfoundlands, Labrador Retrievers, Mastiffs, English and French Bulldogs, Dachshunds, Chihuahuas and Scottish Terriers. The vast majority of cystine stones come from younger intact males, and some types depend on male hormones. Bilirubin crystals are most common in dogs, and small numbers may be normal.
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.
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.