Physical Examination
Color, Clarity, and Odor
How urine color, clarity, and odor are assessed and interpreted with chemical and microscopic findings.
Color and clarity provide immediate but subjective information about a urine specimen. Neither observation is diagnostic when considered alone. Both should be interpreted with reagent-strip and microscopic findings, particularly when the results do not agree.
Under CAP accreditation, a complete routine urinalysis must include glucose, protein, blood, leukocyte esterase, specific gravity, and nitrite. Color, clarity, and odor are optional. Laboratories may report these observations as additional clinical context.
Color
Color is assessed on a well-mixed specimen in a clear container, against a white background, and under adequate lighting. Consistent terminology should be used for reporting. Normal results are commonly described as pale yellow, yellow, or dark yellow.
The principal pigment responsible for the normal yellow color of urine is urochrome. Terminology varies among references. Some chemical references use urochrome and urobilin, the oxidation product of urobilinogen, for the same compound. Standard urinalysis texts commonly distinguish them and describe urobilin as a minor pigment that increases as a specimen stands. This difference in terminology does not affect routine interpretation. Urobilinogen is produced in the intestine when the bacterial enzyme BilR reduces bilirubin.
In a fresh specimen, the intensity of yellow color generally reflects urine concentration. Pale urine is usually more dilute, whereas dark yellow urine is usually more concentrated. An unexpected relationship between color and specific gravity requires further evaluation. Uroerythrin is a separate pigment that can color precipitated amorphous urates pink in cold, acidic urine. A pink deposit may therefore develop in a refrigerated specimen without indicating disease.
Abnormal urine color has both pathologic and nonpathologic causes. Diet, medications, and changes during storage can produce colors that resemble those associated with disease. Abnormal color should therefore be interpreted with the chemical and microscopic findings.
| Color | Potential cause | Findings that aid interpretation | Common nonpathologic cause |
|---|---|---|---|
| Dark yellow to amber, or yellow-green | Bilirubin, oxidizing to biliverdin on standing | Persistent yellow foam on shaking, plus a positive strip bilirubin | Concentrated specimen, B-complex vitamins |
| Orange | Phenazopyridine, sulfasalazine | Thick pigment may mask the strip colors; yellow foam can resemble bilirubin | Medication-related discoloration |
| Red, pink, or red-brown | RBCs, free hemoglobin, myoglobin, porphyrins | Strip blood result, plasma color, and microscopy together separate all four | Beets in susceptible people, menstrual contamination, rifampin |
| Brown to black | Homogentisic acid, melanin | Darkens further on standing, alkaline urine especially | Levodopa, methyldopa, metronidazole, chloroquine |
| Blue-green | Pseudomonas infection, indican | Urine culture | Methylene blue, amitriptyline, propofol, food dyes |
Red, pink, or red-brown urine may result from intact RBCs, free hemoglobin, myoglobin, or porphyrins. The reagent-strip blood reaction cannot distinguish these causes without additional information.
Worked example. A specimen is red and has a strongly positive reagent-strip blood reaction, but microscopy shows few or no intact RBCs. This combination suggests hemoglobinuria, myoglobinuria, or RBC lysis in a dilute or alkaline specimen that has been standing. Plasma color can help distinguish the causes: intravascular hemolysis may discolor plasma, whereas myoglobin usually does not.
Clarity
Clarity is assessed on the same well-mixed specimen. Grades are commonly defined by how clearly printed text can be seen through the container. The terminology and limits for each grade are established by the laboratory’s procedure rather than by a universal standard.
A freshly voided clean-catch specimen is normally clear. Turbidity in a fresh specimen may result from either nonpathologic material or clinically significant formed elements.
| Nonpathologic sources of turbidity | Pathologic sources of turbidity |
|---|---|
| Squamous cells and mucus | RBCs, WBCs, bacteria |
| Amorphous phosphates, white, in alkaline urine | Yeast, trichomonads |
| Amorphous urates, pink, in acidic urine | Transitional or renal tubular epithelial cells |
| Semen, fecal contamination | Abnormal crystals |
| Radiographic contrast, talc, vaginal creams | Lymph, lipids |
Amorphous urates dissolve with gentle warming, whereas amorphous phosphates dissolve after acidification. These solubility characteristics can help identify the source of turbidity.
Clarity does not replace microscopy because a clear specimen may still contain clinically significant constituents. However, the degree of turbidity should generally correspond to the amount of material observed in the sediment. A discrepancy may indicate inadequate mixing or a technical or clerical error and should be investigated.
Foam provides limited additional information. Persistent white foam may accompany increased protein, and yellow foam may occur with bilirubin or phenazopyridine. These observations do not replace reagent-strip testing or quantitative protein measurement.
Odor
Odor is not routinely reported and is rarely diagnostic. Sweet or fruity, maple-syrup, mousy, sweaty-feet, cabbage-like, and ammoniacal odors have historically been associated with ketones, specific inborn errors of metabolism, or bacterial decomposition. These associations are nonspecific and do not replace newborn screening, confirmatory metabolic testing, or the evidence required to diagnose a urinary tract infection.
Specimens should not be smelled deliberately. An unusual odor noticed during routine handling may be communicated when permitted by the laboratory’s procedure, but it should be treated as a nonspecific observation.
References
- Kouri TT, Hofmann W, Falbo R, et al. The EFLM European Urinalysis Guideline 2023. Clin Chem Lab Med. 2024;62(9):1653-1786.
- Hall B, Levy S, Dufault-Thompson K, et al. BilR is a gut microbial enzyme that reduces bilirubin to urobilinogen. Nat Microbiol. 2024;9:173-184.
- College of American Pathologists. Urinalysis Checklist, 12/09/2025 edition, Urinalysis Parameters. A CAP accreditation requirement, not a regulation.