Why is Urine Specific Gravity Low? Causes, Symptoms, and What to Do

A low urine specific gravity means your urine is more dilute than usual, with a lot of water and relatively few dissolved particles. A common and harmless reason is simply having drunk a lot of fluid; less often it means the kidneys cannot concentrate urine properly, as in diabetes insipidus, kidney infection or kidney disease. The reading is a sign rather than a disease: what matters is whether it stays low and whether there are other findings.

What urine specific gravity measures

Specific gravity compares the density of your urine with that of water. It gives a rough measure of how concentrated the urine is, that is, of the total amount of dissolved particles in it. It is usually one part of a routine urinalysis and is measured with a dipstick, a refractometer or a hydrometer. A related test, urine osmolality, is more precise; specific gravity is used because it is quicker and more convenient.

Typical reference values

Ranges vary slightly between laboratories, so compare your value with the range on your report. Values below the lower limit mean dilute urine; values above 1.030 mean concentrated urine.

Causes of low urine specific gravity

Common and usually benign

• Drinking a lot of fluid. Extra water is passed out in the urine, diluting it.
• Older age. Kidneys in older people are less able to concentrate urine, so readings can be lower.
• Diuretics (water pills). These medicines make the kidneys pass more water, so the urine can be dilute; mention them to whoever interprets the test, but do not stop them on your own.

Less common, worth investigating if the value stays low

• Chronic kidney disease or kidney failure. Damaged kidneys lose the ability to concentrate urine.
• Diabetes insipidus. Either the body makes too little antidiuretic hormone (ADH), the hormone that tells the kidneys to save water, or the kidneys do not respond to it; large amounts of dilute urine are passed.
• Severe kidney infection (pyelonephritis) and renal tubular necrosis, damage to the kidney tubules that normally reclaim water.
• Low blood sodium (hyponatremia).
• Low blood potassium or high blood calcium, which can both reduce the kidneys' ability to concentrate urine.

Measurement effects

• Dipstick reading and urine pH. Dipstick specific gravity can read falsely low when urine pH is above 7, and falsely high when pH is below 6.

Causes of high urine specific gravity

Concentrated urine is most often due to dehydration, including from vomiting or diarrhoea. Other listed causes are glucose in the urine (as in poorly controlled diabetes), heart failure, high blood sodium, reduced blood flow to the kidneys, shock, Addison disease and the syndrome of inappropriate ADH secretion (SIADH). Large molecules such as glucose, albumin (a protein) and X-ray contrast dye can also raise the reading measured by refractometer or hydrometer, which is why you should mention a recent CT or MRI scan with contrast.

Symptoms

A low specific gravity does not cause symptoms. Any symptoms come from the cause. Excessive thirst and passing large amounts of urine are among the reasons doctors check water balance and the kidneys' concentrating ability. If you simply drank a lot before the test, the low reading itself means nothing is wrong.

What usually happens next

• Repeat the test, sometimes after limiting fluids for 12–14 hours beforehand if your clinician asks, to see whether the kidneys can concentrate urine.
• Urine osmolality, the more precise measure of urine concentration. After 12–14 hours without fluids, healthy kidneys usually produce urine above 850 mOsm/kg.
• Blood tests: serum osmolality, sodium, a comprehensive metabolic panel and blood urea nitrogen (BUN) to look at kidney function and water balance.
• Imaging such as a kidney ultrasound, CT or MRI, if kidney disease is suspected.
• Measuring urine volume and, when diabetes insipidus is suspected, a supervised water-deprivation test.

Tell the person taking the sample about all medicines and supplements, recent contrast dye or anaesthesia, and whether you are menstruating, since these can affect results. Do not stop any medicine unless your clinician tells you to.

Frequently asked questions

What does low specific gravity in urine mean? Your urine is dilute. Most often it means you drank plenty of fluid before the test, or that you take a diuretic (water pill). If it stays low on repeat testing, especially with thirst and large urine volumes, the kidneys' concentrating ability or ADH may be checked.

Is low urine specific gravity dangerous? Not by itself. It is a sign, not a disease. It matters only when it reflects an underlying condition such as diabetes insipidus or kidney disease.

Can dehydration cause low urine specific gravity? No, dehydration usually raises specific gravity because the kidneys hold on to water and the urine becomes concentrated.

What does elevated specific gravity in urine mean? Your urine is concentrated, most often because of dehydration, vomiting or diarrhoea. It can also be raised by glucose in the urine, heart failure, SIADH, Addison disease or contrast dye.

What causes high urine specific gravity? The listed causes are dehydration, glucose in the urine, heart failure, high blood sodium, reduced blood flow to the kidneys, shock, Addison disease and SIADH.

Do I need to prepare for a specific gravity test? Usually not, but your clinician may ask you to limit fluids for 12–14 hours to test how well the kidneys concentrate urine.

What is the difference between urine specific gravity and urine osmolality? Both describe how concentrated urine is. Specific gravity is a quick, convenient part of a routine urinalysis and gives a rough measure; urine osmolality is the more specific and precise test. Because specific gravity is easier to do and is already part of most urine tests, osmolality is often not needed unless the doctor wants a more exact answer, for example alongside blood osmolality.

When to see a doctor

It is worth discussing your result with your doctor soon if specific gravity stays low on repeat tests, or if you are constantly thirsty, passing large amounts of urine, or have known kidney disease. Seek urgent care for confusion or fainting.

Sources

1. Urine specific gravity test — MedlinePlus (U.S. National Library of Medicine)
2. Urine-Specific Gravity — Cleveland Clinic
3. Evaluation of the Patient With Renal Issues — Merck Manual Professional Version
4. Osmolality urine test — MedlinePlus (U.S. National Library of Medicine)
5. Hypernatremia — Merck Manual Professional Version
6. Urinalysis — StatPearls (NCBI Bookshelf)

Decisions about your health should always be made in consultation with your healthcare provider.