Bedside Snapshot
- Normal (Adult)
- 1.005–1.030 (typical; lab-specific)
Unitless density ratio, not a count of solute particles - Critical Values
- No universal critical value. Interpret by trend, serum sodium and clinical context (typical; lab-specific)
- High Suggests
- Volume depletion: vomiting, diarrhea, fever, hemorrhage
- ADH excess (SIADH) with low serum sodium
- Glucose, protein, mannitol or contrast (falsely high)
- Low Suggests
- Excess water intake or IV fluid
- Diabetes insipidus (central or nephrogenic)
- Loop diuretics (urine near 1.010 even when dehydrated)
- Kidney tubular injury (fixed near 1.010 suggests severe loss)
- Act Now If
- Large volume of dilute urine with rising serum sodium, or SG fixed near 1.010 with rising creatinine: check serum sodium, osmolality, glucose and creatinine; notify the provider now
- Watch Out For
- A dipstick SG is less reliable than refractometry and read higher than the refractometer in one chemotherapy study. Do not judge hydration or chemotherapy hydration from a dipstick SG alone
Reference & Critical Ranges
Lab-specific ranges: Each lab sets its own interval, and it varies by analyzer and population. Use the range on your lab report. The values below are typical.
Reference ranges
| Population | Conventional | SI | Notes |
|---|---|---|---|
| Adult | 1.005–1.030 | Unitless (relative density) | Typical. Lower limit varies: some labs use 1.003, so 1.003–1.005 is a gray zone. The first-morning sample after overnight fluid restriction is the most concentrated |
| Pregnancy | — | — | No pregnancy-specific interval verified; use the lab interval and the trend |
| Older adult | Lab-specific | — | Concentrating ability tends to fall with age |
| Children and neonates | Lab-specific | — | Neonates concentrate urine less well than adults; use the lab pediatric interval. Dipstick SG was unreliable in a pediatric comparison (reference 1) |
Severity & critical values
| Level | Specific gravity | What it means |
|---|---|---|
| Dilute | <1.005 (gray zone 1.003–1.005, lab-dependent) | Kidneys are not concentrating: excess water intake, diabetes insipidus or kidney tubular injury. Loop diuretics give dilute or near-isosthenuric urine (about 1.010) |
| Typical | 1.005–1.019 | Adequate concentrating ability for the clinical setting; SIADH urine is often moderately concentrated (about 1.010–1.020) |
| Concentrated | 1.020–1.030 | Expected with volume depletion or ADH effect; within the normal range |
| Very high | >1.030 | Unusual for urine (maximal human urine concentration is about 1.030–1.035); suspect glucose, protein, osmotic agents or iodinated contrast first |
| Fixed | About 1.010 on repeated samples | Isosthenuria: SG does not change with hydration; severe loss of concentrating and diluting ability |
| Critical | No universal value | Judge by trend, serum sodium, osmolality and the clinical picture |
Critical values: There is no universal critical value for specific gravity. SG screens hydration and kidney concentrating ability. Read it next to serum sodium, osmolality and the clinical picture (typical, lab-specific).
Conversion: None. SG has no units. For solute concentration, the direct measure is urine osmolality (mOsm/kg).
Causes of Abnormal Results
High (SG 1.020 and above)
| Mechanism | Common causes | Bedside clue |
|---|---|---|
| Volume depletion | Vomiting, diarrhea, fever, hemorrhage, poor oral intake | Low urine output, dry mucosa, tachycardia, orthostasis |
| Reduced effective volume | Heart failure, cirrhosis, sepsis | Edema or shock picture with low urine output; ADH release is driven by low perfusion |
| ADH excess (SIADH) | CNS disease, pulmonary disease, malignancy, drugs such as SSRIs and carbamazepine | Low serum sodium with urine that is not dilute and no volume depletion; SIADH urine is often only moderately concentrated (about 1.010–1.020) |
| Glycosuria | Uncontrolled diabetes; SGLT2 inhibitors | Glucose on the urine dipstick; SG overstates concentration |
| Proteinuria | Nephrotic syndrome, glomerular disease | Heavy protein on urinalysis; SG overstates concentration |
| Osmotic and radiopaque agents | Mannitol, dextran, IV iodinated contrast | Recent infusion or CT; refractometer SG can read higher than the dipstick |
Falsely high SG: Glucosuria, proteinuria or contrast push SG up. That high number does not mean the kidneys are concentrating well. Check osmolality.
Low (SG below 1.005)
| Mechanism | Common causes | Bedside clue |
|---|---|---|
| Excess water intake | Psychogenic polydipsia, large oral or IV fluid loads | Large volume of pale urine; low serum sodium |
| Diabetes insipidus | Central (ADH deficiency) or nephrogenic (kidney does not respond to ADH) | Large volume of dilute urine with rising serum sodium; needs urgent evaluation |
| Loop diuretic effect | Furosemide, bumetanide | Dilute or near-isosthenuric urine (about 1.010) even when the patient is dehydrated |
| Electrolyte effect | Hypokalemia, hypercalcemia | Check potassium and calcium |
| Kidney impairment | Acute tubular injury, chronic kidney disease, interstitial nephritis | Rising creatinine; SG fixed near 1.010 |
Isosthenuria (SG fixed near 1.010)
When SG stays about 1.010 across samples with different hydration, the kidneys can neither concentrate nor dilute urine. One sample does not prove it.
- Usual setting: advanced kidney impairment. Confirm it with creatinine and eGFR.
- Not a diagnosis by itself: Read it with the clinical picture and serum chemistry.
Interpretation & Bedside Approach
Step-by-step approach
- Is it real? Confirm the method (refractometer or dipstick). Check for glucose, protein, contrast or mannitol, which raise SG.
- How sick is the patient? Check perfusion, mental status, urine output and fluid losses. SG alone does not measure volume status.
- Acute or chronic, and what is the trend? A single SG is weak evidence. Repeat it or follow urine output.
- Pair it with serum sodium and osmolality. High SG with low sodium points toward ADH excess; dilute urine with high sodium points toward diabetes insipidus.
- Use osmolality when SG is unreliable or the question is ADH. Urine osmolality counts solute particles; SG measures density.
- Escalate or dispose. Treat the cause. Refer urgently for a diabetes insipidus pattern, rising creatinine or unexplained hyponatremia.
Patterns and what they suggest
| Pattern | Suggests |
|---|---|
| Urine not dilute (SG often 1.010–1.020 or higher), low serum sodium, not volume depleted | SIADH pattern; confirm with urine and serum osmolality and urine sodium |
| Low SG, rising serum sodium, large urine volume | Diabetes insipidus pattern (central or nephrogenic); urgent evaluation |
| Low SG, low serum sodium, polydipsia | Excess water intake or primary polydipsia |
| Concentrated urine (SG 1.020 or above), low urine output, poor perfusion | Expected kidney response to volume depletion |
| Very high SG (above 1.030) with glucose, protein or contrast | Falsely high SG; use osmolality to judge concentrating ability |
| SG fixed near 1.010, rising creatinine | Advanced kidney impairment; check eGFR and trend |
SIADH criteria: The 2013 expert panel requires urine osmolality above 100 mOsm/kg and serum osmolality below 275 mOsm/kg. Thyroid and adrenal function must be normal. No diuretic can be in use. Urine SG is not part of the criteria.
Confirming diabetes insipidus takes a supervised water deprivation test, then a desmopressin challenge. A bedside SG cannot make that call.
Special Populations
Special populations
| Population | What changes | Clinical implication |
|---|---|---|
| Neonates & infants | Immature tubular concentrating function | Use the pediatric interval; a low SG is less specific for diabetes insipidus |
| Children & adolescents | Intake and acute illness drive urine output | Interpret with weight, serum sodium and urine output |
| Pregnancy | Physiologic changes in GFR and water handling; no verified interval | Use the lab interval and trend; do not diagnose a concentrating defect from one sample |
| Older adults | Concentrating ability tends to decline | Low SG is more common; interpret with serum sodium and kidney function |
| CKD & dialysis | Loss of concentrating and diluting ability; SG may be fixed | SG cannot show fluid status; use weight, blood pressure and serum chemistry |
| Liver disease | Ascites and hyponatremia alter sodium and water handling | Pair SG with serum sodium and a volume examination |
Interfering Factors & Pitfalls
Collection and handling
| Factor | Effect | Why | Avoid / fix |
|---|---|---|---|
| Delayed analysis | Unpredictable | Bacterial and chemical change in standing urine | Analyze promptly; follow the lab specimen-stability rule |
| Large recent fluid intake | ↓ | Recent drinking dilutes the sample | Use the first-morning void to judge concentrating ability |
Medications and substances
| Factor | Effect | Why | Avoid / fix |
|---|---|---|---|
| Loop diuretics (furosemide) | ↓ | Impair the medullary concentrating mechanism | Note the last dose; expect dilute urine even when dehydrated |
| Mannitol, dextran | ↑ (refractometer) | Large osmotic or colloid molecules raise density | Use osmolality for concentrating ability |
| IV iodinated contrast | ↑ (refractometer) | Radiopaque molecules add density | Repeat the sample or measure osmolality; do not treat as dehydration |
| Glucose (glycosuria, SGLT2 inhibitors) | ↑ (refractometer); dipstick less affected | Dissolved glucose adds density and refractive index; the ion-based dipstick reagent responds less | Use osmolality; SG overstates concentration |
Physiologic and assay factors
| Factor | Effect | Why | Avoid / fix |
|---|---|---|---|
| Protein (proteinuria) | ↑ (refractometer); dipstick less affected | Large molecules add density | Use osmolality |
| Urine pH (dipstick) | Misread (↓ at high pH) | Strip chemistry depends on pH, not only solute density; manufacturers apply a pH correction to the strip reading | Use a refractometer when pH is extreme or results disagree |
| Colored urine (methotrexate) | May distort the strip color read | Yellow or fluorescent urine may distort the color read (a proposed mechanism) | Use a refractometer |
| Dipstick vs refractometer | Discordant results; dipstick often reads higher | The dipstick reagent responds mainly to ions (a general mechanism, not specific to chemotherapy); refractometer responds to all dissolved particles | Use the refractometer for decisions; discrepancies can exceed 0.01 |
Common misinterpretations
- SG measures density. It does not count solute particles.
- Glucose or contrast can push SG high. That number does not prove normal concentrating ability.
- A normal SG does not clear the patient of dehydration.
- One low value does not diagnose diabetes insipidus. Confirm with osmolality and the water deprivation test.
Do not decide hydration-based treatment from a dipstick SG alone: Chemotherapy hydration counts too. Get a refractometer or osmolality reading before you act.
Physiology & Test Basics
What it measures
Urine specific gravity compares the density of urine with pure water, which is 1.000. It tracks the dissolved solids, mainly salts, urea and glucose. Here it works as a screen for hydration and kidney concentrating ability. Osmolality is the direct measure.
Physiology & regulation
- ADH (vasopressin): The posterior pituitary releases it when plasma osmolality rises or effective volume falls. It makes the collecting duct hang on to water.
- Medullary gradient: The loop of Henle and the medullary interstitium build the osmotic gradient. That gradient is what makes concentrated urine possible.
- Dilution: Without ADH, the distal nephron lets dilute urine out. SG falls.
- Solute load: The urea and salt the kidneys must excrete set how much water goes with them.
How it is measured
Collect a random or first-morning sample in a clean, sealed container. A refractometer (lab or bedside) beats the dipstick for reliability. You can also use a reagent strip (dipstick) or a urinometer. Run it promptly, because delay changes the sample. Bedside turnaround takes minutes. Elsewhere it depends on the lab.
Why it matters
SG is a quick, cheap clue about hydration and about how well the kidney concentrates or dilutes urine. Read it with serum sodium and urine output. Then it helps you separate volume depletion, ADH excess and diabetes insipidus at the bedside.
Clinical Pearls
Refractometer over dipstick: The refractometer beats the dipstick, but it still only approximates osmolality, the reference. Dipstick readings can sit more than 0.01 away from the refractometer. When the number would change management, get the osmolality.
EMS and transport: You will rarely have a urine SG in the field. Read hydration from mental status, skin, mucous membranes, perfusion and urine output. Then write the output down for the receiving team.
Large dilute urine with rising sodium: Assume diabetes insipidus until proven otherwise. Check serum sodium and osmolality, then notify the provider or medical control now.
Low sodium with urine that is not dilute: Not volume depleted? Think SIADH. Confirm it with urine and serum osmolality and urine sodium. SG alone will not get you there.
Diuretics blur the picture: Furosemide can leave the urine dilute while the patient is still dehydrated. Write down the last diuretic dose before you read the SG.
Contrast CT: After IV contrast, a high refractometer SG is artifact, not dehydration. Repeat the sample or check osmolality before you act.
Trend beats one number: A series of urine outputs and serum sodium values says more than one SG. When the result and the bedside disagree, repeat the test.
References
- Roessingh A, Drukker A, Guignard J. (2001). Dipstick measurements of urine specific gravity are unreliable. Archives of Disease in Childhood, 85(2), 155–157 (landmark comparison study). https://pmc.ncbi.nlm.nih.gov/articles/PMC1718890
- Sethi et al. (2010). Is specific gravity a good estimate of urine osmolality? Journal of Clinical Laboratory Analysis, 24(6), 426–430. https://pmc.ncbi.nlm.nih.gov/articles/PMC6647580
- Fan S-L. (2021). Can dipsticks be used for specific gravity in urine samples from chemotherapy? ADLM Scientific Short. https://myadlm.org/science-and-research/scientific-shorts/2021/can-dipsticks-be-used-for-specific-gravity-in-urine-samples-from-chemotherapy
- Verbalis JG, Goldsmith SR, Greenberg A, Korzelius C, Schrier RW, Sterns RH, Thompson CJ. (2013). Diagnosis, evaluation, and treatment of hyponatremia: expert panel recommendations. The American Journal of Medicine, 126(10 Suppl 1), S1–S42. https://doi.org/10.1016/j.amjmed.2013.07.006
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