Understanding High Urine Specific Gravity: Causes & What They Mean

Urine Specific Gravity (USG)

Ratio of urine density to water density. Normal: 1.005–1.030. High USG (>1.030) = concentrated urine.

Major Causes

1. Dehydration (Most Common)

• Inadequate intake, excessive loss (sweat, diarrhea, vomiting, fever, burns, diuretics).
• ADH ↑ → maximal water reabsorption in collecting ducts.

2. Proteinuria

Protein (mostly albumin) increases solute mass → ↑ USG. Causes: glomerular disease (GN, FSGS), diabetic nephropathy, myeloma (Bence Jones), preeclampsia, orthostatic proteinuria.

3. Glycosuria

Glucose > renal threshold (~180 mg/dL) → osmotic diuresis paradoxically concentrates remaining urine. Diabetes mellitus, renal glycosuria, pregnancy, Fanconi syndrome.

4. Ketonuria

Ketones (acetoacetate, β-hydroxybutyrate) are dense solutes. Starvation, ketogenic diet, uncontrolled DKA, alcoholism, pregnancy.

5. Radiocontrast / Mannitol / IVIG

Exogenous osmoles excreted renally → transiently ↑ USG.

6. SIADH / Heart Failure / Cirrhosis / Renal Failure

Effective arterial blood volume depletion → ADH ↑ → water retention → concentrated urine (despite total body water excess).

Interpretation Nuances

• USG depends on number of particles, not just water. High solute excretion (protein, glucose, ketones, contrast) elevates USG even if hydrated.
• Urine osmolality (mOsm/kg) is more precise (normal 300–900; max 1200–1400).
• Fixed low USG (1.008–1.012) = renal concentrating defect (DI, CKD, tubulointerstitial disease).

Clinical Action

High USG + dehydration signs → fluid repletion. High USG + edema/volume overload → treat underlying cause (HF, cirrhosis, SIADH). Proteinuria/glucosuria/ketonuria → disease-specific workup.