Urine cytology: what the test is, how accurate it is and when it is used

The lining of the bladder and the rest of the urinary tract constantly sheds cells into the urine. In urine cytology, a sample is sent to a pathology laboratory where the cells are prepared and examined under a microscope by a specialist who looks for cells that look abnormal. It is not a chemical test. It is not the same as a dipstick, a urine culture for infection, or a urine test for blood.

In the large UK research study that most directly addresses its role (the DETECT I study of 3,556 people referred to hospital with blood in the urine), a positive cytology was defined as a result "suspicious for neoplastic cells or atypical cells". Reports can therefore be graded, for example negative, atypical, suspicious or positive, and the grade matters when deciding what to do next.

Because it is a cell test, it depends on there being enough suitable cells in the sample to examine. Collection instructions differ between hospitals, so your own hospital or GP will tell you which container to use, when to collect and where to hand it in.

The NHS says that if a GP refers you to a urologist because they think you could have bladder cancer, you will have tests to check for cancer, that you may have another urine test, and that the main test is a cystoscopy. Cytology, where it is used at all, sits alongside those investigations rather than ahead of them.

A BAUS (British Association of Urological Surgeons) conference poster from a teaching hospital and cancer centre noted that, although guidance has suggested urine cytology for the diagnosis of bladder cancer, it is infrequently performed because of suboptimal sensitivity, cost and uncertainty in interpreting results, particularly atypical results. In that review of 500 two-week-wait haematuria cases, all bladder cancers were identified by cystoscopy or routine imaging, irrespective of cytology.

Cytology may still have a place in select situations. The poster found that suspicious or malignant cytology was associated with higher-risk cancers and suggested it could be used to help prioritise waiting lists for tumour resection. The main haematuria study similarly concluded that the role of cytology in select cases should be considered in the context of the impact of a false-positive result leading to further invasive tests, sometimes under general anaesthesia.

In the DETECT I analysis, cytology was performed in 567 patients from nine hospitals. Bladder cancer was found in 39 patients (6.9%) and upper tract urothelial cancer in 8 (1.4%). Sensitivity was 43.5%, specificity 95.7%, positive predictive value 47.6% and negative predictive value 94.9%. In plain terms, fewer than half of the cancers were picked up by cytology, and roughly half of the positive results were true positives.

Cancers missed included some higher-risk ones. Of the 21 bladder cancers missed, 4 (19%) were muscle-invasive or beyond and 2 (9.5%) were high-grade T1 tumours, and the researchers concluded that cytology will miss a significant number of muscle-invasive and high-risk disease. False-positive cytology results occurred in 22 patients; 12 of these had further invasive tests and 5 had a repeat cytology, and no cancer was identified in them during follow-up.

The strengths are on the negative side: a negative cytology was usually correct in that population. But given the sensitivity figure, a negative cytology cannot be used on its own to rule out cancer, which is why it is read with cystoscopy and imaging.

A negative result means no abnormal cells were seen in that sample. It is reassuring only in the context of the whole work-up; it does not replace cystoscopy and imaging. An atypical result means some cells looked unusual but not clearly cancerous, and the BAUS poster found that, in the presence of negative haematuria investigations, atypical cytology did not appear to be associated with malignancy and so should not by itself alter management.

A suspicious or positive result means that cells appeared to have cancerous features. That is not a diagnosis. Confirmation comes from a biopsy or tumour resection. In the DETECT I study the reference standard for a diagnosis was histological confirmation of cancer, and the median time between a positive cytology and endoscopic tumour resection was 27 days.

If your cytology is reported as suspicious but a camera examination and imaging are normal, your urology team may repeat tests or arrange closer follow-up. If you have been told your result is abnormal, ask the clinician who requested it what they plan to do, and what they will check next.

For most people, cytology if it is done at all is part of a sequence. The NHS says that if you are told you have bladder cancer you will usually need more tests, such as an ultrasound, MRI or CT scan, blood tests or a bone scan, to find the size, type and stage. It also says you may get your results on the same day or after a few days and that a clinical nurse specialist will be your main point of contact.

Cancer Research UK says you usually have a few tests to find out whether symptoms could be due to bladder cancer, and then more tests to find out how far it has grown if cancer is found. Your specialist will decide which are needed.

• Cystoscopy, with a biopsy if an area looks abnormal.

• Imaging of the kidneys and upper urinary tract, such as ultrasound or CT urogram.

• Further urine tests where there is a reason for them.

• Staging scans and blood tests if cancer is confirmed.