A “Flag A” on a urine test report stands for “abnormal,” meaning that one or more measured values fell outside the laboratory’s established reference range. It does not, by itself, tell you what is wrong or even that something is definitely wrong. Laboratories apply this flag automatically whenever an analyzer detects a result that deviates from what is expected in a healthy person’s urine, and the reasons can range from a genuine infection or metabolic problem to something as mundane as not drinking enough water before the test.
How the Flag Gets Generated
Most hospital and clinic laboratories use automated analyzers that combine chemical reagent strips (dipsticks) with flow cytometry or digital imaging to evaluate urine. The dipstick side detects substances like protein, glucose, blood, and nitrites through color-change reactions. The flow cytometry side counts and classifies individual particles in the sample, including red blood cells, white blood cells, bacteria, epithelial cells, and casts, and it flags unusual findings such as pathological casts, yeast-like cells, crystals, and other atypical particles.1Oxford Academic (Clinical Chemistry). Routine Workflow for Use of Urine Strips and Urine Flow Cytometer UF-100 in the Hospital Laboratory When either side produces a result that crosses a threshold set by the lab, the report generates a flag. In most electronic health records, that flag appears as the letter “A” next to the value, sometimes highlighted in red or bold.
The thresholds themselves are not universal. Each laboratory sets its own reference ranges based on the population it serves, the analyzer it uses, and manufacturer recommendations. A value flagged as abnormal at one lab might technically fall within the normal range at another, especially for parameters like pH or specific gravity where the expected window is fairly wide. This is one reason why comparing results from two different labs can be confusing.
Common Parameters That Trigger a Flag
A standard urinalysis panel checks roughly ten chemical parameters and, when microscopy is included, several types of cells and structures. Here are the ones that most often produce an “A” flag and what they can point to.
Red Blood Cells and Hemoglobin
The dipstick detects hemoglobin, the pigment inside red blood cells, through a peroxidase reaction. If it turns positive, the report will flag blood in the urine. The automated microscopy or flow cytometry component then counts actual intact red blood cells. A mismatch between the two, such as a positive dipstick for hemoglobin but few red blood cells under the microscope, can mean the red cells broke apart before analysis. Research has shown that urine with a pH below about 6.0 and a low-level hemoglobin reading is less likely to still contain intact red blood cells in the sediment, because acidic urine tends to lyse them.2PubMed. Determination of red blood cells in urinary sediment: Do pH and specific gravity of urine matter? When a flag appears for blood, the lab or your provider will want to know whether you had strenuous exercise recently, are menstruating, or have a kidney or bladder issue that needs follow-up.
White Blood Cells, Leukocyte Esterase, and Nitrites
These three are the workhorses of urinary tract infection screening. Leukocyte esterase is an enzyme released by white blood cells, and nitrites are produced when certain bacteria convert naturally occurring nitrates in urine. A flag on either one raises suspicion for infection. Current clinical practice combines these dipstick results with symptom history and sometimes a white blood cell count to decide whether to send a urine culture.3PubMed. New markers of urinary tract infection
A flagged leukocyte esterase or nitrite result is not proof of infection, though. In a study of ambulatory women with suspected uncomplicated UTIs, roughly one in five urine samples that actually contained significant bacterial growth had negative dipstick results for both leukocyte esterase and nitrites.4PubMed Central. Evaluation of the leukocyte esterase and nitrite urine dipstick screening tests for detection of bacteriuria in women with suspected uncomplicated urinary tract infections The reverse also happens: a positive flag does not guarantee bacteria will grow in culture. Vaginal contamination, certain medications, and inflammation from non-infectious causes can all push leukocyte esterase above the threshold. This is why a flag here often prompts a urine culture rather than immediate antibiotic treatment.
Glucose and Ketones
Glucose normally stays out of urine because the kidneys reabsorb it. When blood sugar rises high enough to overwhelm that reabsorption, glucose spills into the urine and triggers a flag. Ketones appear when the body burns fat instead of glucose for fuel, which happens during prolonged fasting, very low-carb diets, uncontrolled diabetes, or heavy exercise. If both glucose and ketones are flagged together, the combination is a clinical red flag for diabetic ketoacidosis, a serious complication driven by insulin deficiency and elevated stress hormones.5PubMed. Overview of the diagnosis and management of diabetic ketoacidosis In someone who is not diabetic, a glucose flag might prompt a blood sugar check to investigate whether diabetes or a kidney tubular problem is the cause.
Protein
The dipstick protein test primarily detects albumin. Small amounts can appear after vigorous exercise, fever, or standing for long periods, a phenomenon sometimes called orthostatic proteinuria. Persistent or high-level protein flags raise concern about kidney damage. Interestingly, some patients have casts detected under microscopy yet test negative for protein on the dipstick, because the dipstick mainly detects albumin and can miss smaller proteins. In one study, patients with negative dipstick protein results but positive casts on microscopy still had elevated levels of microalbumin and other small proteins when tested with more sensitive assays.6PubMed Central. Diagnostic value of urinary microprotein concentration for patients with negative urinary protein test results and positive urinary casts on microscopic examination A protein flag, especially a recurring one, usually prompts a more detailed kidney workup.
pH and Specific Gravity
These two values provide context for everything else on the report. Urine pH can range from about 4.5 to 8.0 depending on diet, hydration, and the body’s acid-base status.7Medicine. Laboratory investigations What to do with patients with abnormal dipstick urinalysis A single abnormal pH reading in isolation is hard to interpret, but a strongly alkaline sample might point to a UTI caused by urease-producing bacteria, which convert urea to ammonia and drive the pH up. Specific gravity reflects how concentrated the urine is. Measuring it helps clinicians assess hydration status, distinguish between certain types of kidney injury, and adjust how much weight to give other results on the panel.8PubMed. Relative density of urine: methods and clinical significance Very dilute urine can cause other analytes to fall below their detection threshold, potentially masking a problem. Very concentrated urine can push values above the threshold, producing a flag that disappears once you’re better hydrated.
Why Flags Sometimes Mislead
An abnormal flag is not a diagnosis. It is a screening signal, and screening signals come with both false positives and false negatives. Several common situations generate flags that do not reflect an actual medical problem.
Sample contamination is one of the most frequent culprits, especially with clean-catch specimens collected at home or in a busy clinic. Squamous epithelial cells from the skin around the urethra can get into the sample and suggest contamination. However, research has shown that the squamous epithelial cell count is actually a poor predictor of whether the urine culture itself will be contaminated.9PubMed. Urinary Squamous Epithelial Cells Do Not Accurately Predict Urine Culture Contamination, but May Predict Urinalysis Performance in Predicting Bacteriuria So while a note about epithelial cells on your report might make you think the sample was “bad,” the lab does not automatically dismiss the rest of the findings on that basis alone.
Medications and supplements also interfere. High-dose vitamin C can affect the accuracy of the glucose and blood readings on dipsticks. Certain antibiotics can change urine color and confuse colorimetric readings. Beets, blackberries, and rhubarb can turn urine red or pink, mimicking blood. These kinds of interferences are one reason the lab flags the result for review rather than stamping it with a diagnosis.
Automated analyzers occasionally misclassify particles as well. Crystals can be mistaken for other cell types, prompting flags that require a trained technologist to sit down at a microscope and verify.10PubMed Central. Clinical laboratory automated urinalysis: comparison among automated microscopy, flow cytometry, two test strips analyzers, and manual microscopic examination of the urine sediments Similarly, casts, yeast, sperm, and dysmorphic red blood cells may need manual microscopic confirmation because of misclassification or incongruent dipstick results.11Clinical Chemistry. Quantitative Urine Particle Analysis: Integrative Approach for the Optimal Combination of Automation with UF-100 and Microscopic Review with KOVA Cell Chamber The presence of a flag sometimes just means the machine said “I’m not sure about this one, a human should look.”
Microscopic Flags and Casts
If your report includes a microscopy section, you might see flags for casts, which are tiny cylindrical structures that form inside the kidney’s tubules. Hyaline casts, made of a protein called Tamm-Horsfall protein, are relatively common and can appear after exercise or dehydration. They are often not clinically significant. But other types, such as red blood cell casts or granular casts, point to specific kidney diseases and are always worth investigating.
Automated analyzers have gotten good at counting common cells, but they still struggle with certain findings. Flow imaging and flow cytometry can accurately identify and quantify normal cells, yet they may miss specific cellular casts, lipid-containing structures, and acanthocytes (a type of misshapen red cell associated with kidney disease).12Advances in Kidney Disease and Health. Urine Sediment Evaluation When the machine flags something unusual in this category, it often triggers a manual review under the microscope, which remains the gold standard for sediment analysis.
What Happens After a Flag
Many laboratories use what is called reflex testing, where a flagged urinalysis automatically triggers additional tests without the ordering provider having to request them separately. The most common example involves urine cultures. Under conditional reflex policies, the lab holds the urine sample for 48 to 72 hours and only sends it for culture if specific criteria on the urinalysis are met, or if the provider explicitly requests it.13PubMed Central. Conditional reflex to urine culture: Evaluation of a diagnostic stewardship intervention within the Veterans’ Affairs and Centers for Disease Control and Prevention Practice-Based Research Network This approach cuts down on unnecessary cultures and the overtreatment that can follow from culturing urine that was flagged for a non-infectious reason.
Other reflex pathways exist too. A flagged protein result might automatically trigger a urine albumin-to-creatinine ratio. A flagged glucose result in someone not known to be diabetic might prompt a blood glucose or hemoglobin A1c order. The point of these cascades is to move from a screening-level flag to a more definitive answer without delay.
How Pregnancy Changes What “Normal” Looks Like
If you are pregnant and see a Flag A on your urinalysis, it is worth knowing that pregnancy shifts many biochemical reference ranges. Increased blood volume, changes in kidney filtration rate, and hormonal fluctuations can all cause values to move outside the standard ranges built into the analyzer’s software. Physiological changes in pregnancy may cause results to be misinterpreted as abnormal, or they can mask a genuine pathological state.14PubMed Central. Changes in biochemical tests in pregnancy and their clinical significance Trace protein in the urine of a pregnant person in the first trimester, for example, might be a normal consequence of increased kidney blood flow. That same result in the third trimester could signal preeclampsia. The flag itself looks the same on the report; the clinical context is what matters.
Some laboratories maintain pregnancy-specific reference ranges, but many do not. If your results were run through standard adult thresholds, a flag may simply reflect the expected physiological changes rather than a problem. Your provider should be interpreting the results with your gestational age in mind.
Reading Flagged Results on a Patient Portal
Increasingly, patients see their lab results on electronic portals before their provider has had a chance to review and explain them. Seeing one or more values marked with “A” can cause real anxiety. Research bears this out: patients who received an abnormal result through an online portal were more likely to experience negative emotions compared to those who received normal results, and they were also more likely to call their physician afterward.15Journal of the American Medical Informatics Association. Patient perceptions of receiving test results via online portals: a mixed-methods study
A few things can help if you find yourself staring at a flagged urinalysis on your phone. First, check whether the result has a reference range listed next to it and see how far outside that range your value falls. A pH of 5.0 when the listed range is 5.0–8.0 is technically at the edge but not alarming. A white blood cell count ten times the upper limit of normal is a different story. Second, look at the whole panel together rather than fixating on one line. A single flagged value with everything else normal often means less than multiple flags pointing in the same direction. Third, if the portal has a section for provider notes or interpretive comments, read those before drawing conclusions. Many providers add context that a standalone “A” does not convey.
It is also worth remembering that some portals release results in stages. You might see chemistry results hours before microscopy results post, and the microscopy might resolve the concern raised by a chemistry flag, or the other way around. Waiting for the full panel before reacting can save you a stressful afternoon.
When a Flag Actually Matters
With all these caveats about false positives, contamination, and benign explanations, it is fair to wonder when a Flag A should concern you. The short answer is that patterns matter more than isolated readings. A single trace protein result in an otherwise healthy person after a hard workout is not the same as protein showing up on three consecutive urinalyses. A one-time positive for blood during menstruation tells a different story than blood appearing repeatedly in a man with no obvious explanation.
Certain combinations of flags also carry more clinical weight. Positive leukocyte esterase, positive nitrites, and elevated white blood cells together strongly suggest a urinary tract infection, especially if you have symptoms like burning or frequency. Glucose and ketones flagged simultaneously in someone with diabetes warrant urgent evaluation. Red blood cell casts alongside protein suggest a glomerular problem in the kidneys that needs subspecialty referral. In these scenarios, the Flag A is doing exactly what it is supposed to do: drawing attention to something that needs action.
Conversely, a single mildly abnormal specific gravity or pH is almost never worth worrying about on its own. These values fluctuate throughout the day based on what you ate, how much you drank, and when the sample was collected. They become meaningful mainly when they help explain other findings on the panel, like why red blood cells were or were not seen in the sediment despite a positive hemoglobin reading.
Turbidity and Physical Appearance Flags
Some labs also report on the physical appearance of the urine sample, including its color and clarity. Turbid, or cloudy, urine can be flagged because it may indicate the presence of white blood cells, bacteria, crystals, or mucus. Recent research has explored objective ways to quantify turbidity using optical measurements. One study found that a lightness value below a specific threshold could distinguish clear from turbid urine with about 96% accuracy.16PubMed Central. A novel method and classification criteria for analyzing urine turbidity and its relationship with urine dry chemical parameters While most patients will not see optical measurements on their report, a notation like “cloudy” or “turbid” with an associated flag is the lab’s way of saying the sample looked off and the chemical or microscopic findings should be interpreted with that in mind.
Turbidity by itself is not diagnostic. Phosphate crystals can make perfectly normal urine appear cloudy, especially if it has been sitting at room temperature. Mucus from the genital tract, particularly in people with vaginas, can do the same. When turbidity accompanies positive flags for white blood cells and nitrites, the picture becomes more cohesive and more likely to represent an actual infection. When it appears alone, it is usually a footnote rather than a headline.