SG

Specific Gravity of Urine

Urinalysis

What is Specific Gravity of Urine?

Urine specific gravity (SG) measures the concentration of dissolved solutes in urine relative to pure water, providing a simple assessment of the kidney's ability to concentrate and dilute urine. Pure water has a specific gravity of 1.000, and normal urine ranges from 1.002 (very dilute) to 1.030 (very concentrated). The major solutes contributing to urine specific gravity are urea, sodium, chloride, potassium, and creatinine, with smaller contributions from glucose, protein, and other dissolved substances.

The kidneys regulate urine concentration in response to the body's hydration status through the action of antidiuretic hormone (ADH, also known as vasopressin). When the body is dehydrated, ADH levels rise, prompting the kidneys to reabsorb water and produce concentrated urine (high SG). When well-hydrated, ADH decreases, allowing dilute urine production (low SG). Urine specific gravity is measured during routine urinalysis using a refractometer or dipstick method and provides a quick snapshot of hydration status and renal concentrating ability. It is particularly useful for interpreting other urinalysis results, as very dilute or concentrated urine can affect the accuracy of other dipstick tests.

Why It Matters

Urine specific gravity is a rapid, inexpensive indicator of hydration status and kidney function. A fixed specific gravity (isosthenuria, approximately 1.010) despite varying fluid intake indicates loss of renal concentrating ability—an early sign of kidney damage. Very low specific gravity may suggest diabetes insipidus (inability to produce ADH or kidney resistance to it) or excessive fluid intake. Very high specific gravity may indicate dehydration, kidney dysfunction, or abnormal solutes like glucose (diabetes mellitus) or protein. The test also helps interpret other urinalysis results: trace protein in very concentrated urine may be insignificant, while trace protein in dilute urine is more concerning.

Normal Reference Ranges

GroupRangeUnit
Adults (random)1.002–1.030
Typical hydrated1.010–1.025
First morning (concentrated)1.015–1.025

Reference ranges may vary by laboratory. Always compare results to the ranges provided by your testing facility.

What High SG Levels Mean

Common Causes

  • Dehydration (most common cause)
  • Excessive sweating, vomiting, or diarrhea
  • Congestive heart failure (decreased renal perfusion)
  • Diabetes mellitus (glycosuria increases SG)
  • SIADH (syndrome of inappropriate ADH)
  • Proteinuria or contrast dye in urine
  • Adrenal insufficiency

Possible Symptoms

  • Dark yellow or amber-colored urine
  • Thirst and dry mouth
  • Decreased urine output
  • Fatigue and dizziness
  • Headache
  • Concentrated, strong-smelling urine

What to do: If due to dehydration, increase fluid intake—urine should return to a lighter color and lower specific gravity. If consistently elevated despite adequate hydration, evaluate for diabetes mellitus (check glucose), proteinuria, or SIADH. High SG with clinical signs of dehydration may require intravenous fluid replacement. Interpret other urinalysis results (protein, cells) in the context of concentrated urine.

What Low SG Levels Mean

Common Causes

  • Excessive fluid intake (polydipsia)
  • Diabetes insipidus (central or nephrogenic)
  • Chronic kidney disease (loss of concentrating ability)
  • Diuretic medications
  • Acute tubular necrosis (recovery phase)
  • Psychogenic polydipsia

Possible Symptoms

  • Clear, colorless urine
  • Frequent urination (polyuria)
  • Excessive thirst (polydipsia) in diabetes insipidus
  • Nocturia (waking at night to urinate)

What to do: Persistently dilute urine (SG <1.005) despite fluid restriction warrants evaluation for diabetes insipidus (water deprivation test, ADH levels) or chronic kidney disease (creatinine, GFR). If due to excessive voluntary water intake, counsel on appropriate fluid consumption. Fixed SG of 1.010 (isosthenuria) suggests significant renal tubular damage. Review medications that may cause dilute urine, including lithium and diuretics.

When Is SG Testing Recommended?

  • As part of routine urinalysis
  • When assessing hydration status
  • When diabetes insipidus is suspected
  • To evaluate kidney concentrating ability
  • When interpreting other urinalysis results
  • In athletes or workers at risk of dehydration

Frequently Asked Questions

Both measure urine concentration, but they work differently. Specific gravity measures the density of solutes (affected by both the number and weight of particles), while osmolality measures the number of dissolved particles regardless of their size. Osmolality is more precise—large molecules like glucose, protein, and contrast dye can disproportionately increase specific gravity without proportionally increasing osmolality. For routine clinical use, specific gravity is adequate and more practical. Osmolality is preferred for precise evaluation of concentrating ability, particularly in diabetes insipidus workup.
Pale straw to light yellow urine (specific gravity approximately 1.005–1.015) generally indicates adequate hydration. Dark amber urine suggests dehydration, while completely colorless urine may indicate over-hydration. The "pee chart" commonly used in sports medicine correlates color with specific gravity: colors 1–3 (light) indicate adequate hydration, 4–6 (medium yellow to amber) indicate mild dehydration, and 7–8 (dark amber to brown) indicate significant dehydration. Note that certain foods (beets, asparagus), medications, and vitamins (B2/riboflavin) can alter urine color independently of hydration.
Yes. Substances like glucose (in uncontrolled diabetes), protein (in nephrotic syndrome), or radiographic contrast dye can artificially elevate specific gravity, making urine appear more concentrated than it actually is in terms of normal solutes. The dipstick method can also be affected by highly alkaline urine (falsely low) or highly acidic urine (falsely high). For the most accurate assessment, a refractometer measurement is preferred over dipstick. When accuracy is critical—such as in drug testing or diabetes insipidus workup—urine osmolality should be measured directly.

Related Biomarkers

pHUrine pHCrCreatinineNaSodium

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Medical Disclaimer: This information is for educational purposes only and is not a substitute for professional medical advice, diagnosis, or treatment. Reference ranges may vary between laboratories. Always consult your healthcare provider for interpretation of your specific test results.

Disclaimer: SymptomGPT is not a medical diagnosis tool and does not provide medical advice. Always consult a qualified healthcare professional. If you are experiencing a medical emergency, call 911 immediately.