Color, Clarity, and Odor

Color

Assess color on a well-mixed specimen in a clear container against a white background under adequate lighting. Report the observation with terms defined in the laboratory procedure. Common normal categories are pale yellow, yellow, and dark yellow.^{22 Kouri TT, et al. The EFLM European urinalysis guideline 2023. 2024.}

Urochrome is the standard urinalysis term for the principal yellow pigment. Standard urinalysis texts describe urobilin, the oxidation product of urobilinogen, as a separate minor pigment that increases while urine stands. Some chemistry references use urochrome and urobilin as synonyms; urinalysis practice keeps the two pigments distinct. Intestinal bacteria produce urobilinogen when the enzyme BilR reduces bilirubin.^{2,32 Kouri TT, et al. The EFLM European urinalysis guideline 2023. 2024.3 Hall B, et al. BilR is a gut microbial enzyme that reduces bilirubin to… 2024.}

In a fresh specimen, the intensity of yellow color generally reflects urine concentration. Pale urine is usually more dilute, and dark yellow urine is usually more concentrated. When yellow intensity and specific gravity disagree, use the measured specific gravity to assess concentration and examine the chemical and microscopic findings for evidence of an endogenous or exogenous pigment. 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.

Dietary pigments, medications, endogenous pigments, and storage changes can produce the same visible color. The table lists the chemical, microscopic, plasma, and culture findings that separate these sources.^{22 Kouri TT, et al. The EFLM European urinalysis guideline 2023. 2024.}

Clarity

Assess clarity on the same well-mixed specimen used for color. Common reporting categories are clear, hazy, cloudy, and turbid. Reading printed material through the container gives a consistent way to grade transparency. The laboratory procedure defines the term and visual limit for each grade.

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.

Gentle warming can dissolve amorphous urates. In a separate aliquot under a validated procedure, dilute acid can dissolve amorphous phosphates. Clearing supports the proposed precipitate. It does not identify the precipitate by itself. Do not use either treated aliquot for routine chemistry or microscopy, because the treatment changes the specimen.^{22 Kouri TT, et al. The EFLM European urinalysis guideline 2023. 2024.}

Microscopy can detect RBCs, WBCs, bacteria, epithelial cells, or crystals even when the specimen appears clear. In a turbid specimen, the visual grade should generally correspond to the amount of material in the sediment. Marked turbidity with little sediment, or abundant sediment in a clear specimen, prompts review of specimen mixing, examination technique, and specimen identity.^{22 Kouri TT, et al. The EFLM European urinalysis guideline 2023. 2024.}

Persistent white foam may accompany increased protein; the reagent-strip protein pad or a quantitative protein measurement establishes whether protein is increased. Yellow foam may occur with bilirubin or phenazopyridine. The bilirubin pad detects bilirubin, and the medication history identifies phenazopyridine exposure.

Odor

Routine urinalysis reports usually omit odor.

Urine ketone testing determines whether ketones account for a fruity odor. Newborn screening and confirmatory metabolic testing identify an inherited metabolic disorder. Urinalysis, urine culture, and clinical criteria establish a bacterial urinary tract infection.

Never smell specimens deliberately; odor is only a secondary clue. If you notice an unusual odor during routine handling, follow the laboratory procedure for documentation and communication.

Practice