Urinalysis: reading the number and acting on it

Why this value is ordered

A urinalysis is ordered whenever the kidney or urinary tract might be involved: dysuria, flank pain, fever of unknown origin, oedema, hypertension in pregnancy, or a routine screen before surgery. It is cheap, fast, and often the first test that redirects the whole workup.

In an admitted patient it also serves as a baseline. A ward nurse sending a clean-catch sample on day one has something to compare against if the patient later spikes a temperature or their urine output drops. Without that baseline, a new finding on day four has no context.

Interpreting the number in context

Specific gravity reflects the kidney's concentrating ability and the patient's hydration, normally 1.005 to 1.030. A value pinned near 1.010, matching plasma, suggests the kidney has lost the ability to concentrate or dilute urine at all, a finding worth flagging in acute kidney injury.

Protein and glucose are usually absent. Trace protein can appear after exercise or fever and is not automatically pathological, but persistent proteinuria alongside hypertension in a pregnant patient is pre-eclampsia until proven otherwise. Glucose in the urine, glycosuria, tracks a blood glucose above the renal threshold of roughly 180 mg/dL and should prompt a blood glucose check, not a urine recheck.

The dipstick's nitrites and leukocyte esterase are read together. Nitrites turn positive when gram-negative bacteria such as E. coli convert urinary nitrates, and leukocyte esterase reflects white cells responding to that infection. Either alone is suggestive; both together, alongside symptoms, is a strong case for a urinary tract infection and usually triggers a culture before antibiotics start.

Critical values and what to do

Casts change the differential. A cast is a cylindrical structure moulded inside the renal tubule, so its presence tells you the problem sits in the kidney parenchyma, not the bladder or urethra. Red cell casts point to glomerulonephritis, white cell casts to pyelonephritis or interstitial nephritis, and this distinction matters because a lower urinary tract infection does not produce casts at all.

Frank haematuria, especially with clots, needs urgent notification, particularly post-catheterisation or post-biopsy where it can signal bleeding rather than infection. Ketones with glucose and a low pH raise concern for diabetic ketoacidosis and should be correlated with a blood gas and serum glucose immediately, not left for the next round.

A markedly abnormal sediment in a patient who is also oliguric or hypertensive warrants an urgent call to the provider rather than routine charting, since it may represent acute glomerulonephritis needing same-day nephrology input.

Related tests read alongside it

Urinalysis rarely stands alone. Serum BUN and creatinine confirm whether an abnormal urinalysis reflects a functional problem or just a lower tract infection; a positive urinalysis with normal renal function points away from the kidney itself. A urine culture and sensitivity follows a positive nitrite or leukocyte esterase result to identify the organism and guide antibiotic choice.

In pregnancy, urinalysis is read alongside blood pressure and a spot protein-to-creatinine ratio when pre-eclampsia is suspected. In diabetic patients, glycosuria on a urinalysis should prompt a check of HbA1c trends rather than being treated as a new finding in isolation.

Nursing implications

Collection technique changes the result. A contaminated midstream sample can show white cells and bacteria that have nothing to do with the urinary tract, so teach the clean-catch technique explicitly rather than assuming the patient knows it, and send catheter specimens from the sampling port, never the bag.

Document the collection method and time alongside the result, since a sample sitting at room temperature for over an hour allows bacterial overgrowth that mimics infection. Refrigerate or send promptly.

When nitrites and leukocyte esterase are both positive in a symptomatic patient, anticipate an order for empiric antibiotics and a culture, and hold that specimen before the first antibiotic dose goes in if at all possible, since even one dose can suppress culture growth.

What patients ask about it

Patients often want to know why they need to give a urine sample when their complaint is unrelated, such as fatigue or hypertension. Explaining that the kidney reflects systemic disease, from diabetes to autoimmune conditions, helps them see the test as informative rather than incidental.

They also ask why a slightly cloudy or strong-smelling sample matters. Cloudiness can reflect white cells, crystals, or simply concentration from dehydration, and reassurance paired with a straight explanation usually settles the concern faster than a vague answer.