Urine Dipstick Tests
See also Urinalysis and bacterial culture Urinalysis and Bacterial Culture.
Basics
- Chemical urinalysis (dipstick test, strip test) should be carried out when the sample has been cooled to room temperature (otherwise, there will be false positive results).
Red blood cell test
- A negative RBC test will exclude haematuria.
- If the cause is evident, such as a urinary tract infection (UTI) or contamination (menstrual bleeding, sexual trauma), and chemical screening of urine is subsequently negative, no further investigations are needed.
- A positive finding should be confirmed first by urine particle counting carried out twice.
- Causes: systemic disease (such as bleeding diathesis; positive also in patients with rhabdomyolysis), renal or urinary tract disease
- If there is macrohaematuria, always refer the patient to a urologist for renal ultrasound, urinary cytology, in specialized care CT IVU, cystoscopy.
- Microhaematuria, see Haematuria Haematuria
- Depending on clinical examination, basic blood count with platelet count, ESR, CRP, plasma creatinine, eGFR Gfr Calculator, PSA
- If there is asymptomatic, isolated microhaematuria, no further investigations are usually needed.
- Blood pressure monitoring, chemical screening of urine and urine particle counting annually for 5 years, for example (possibly developing glomerulonephritis?)
- Urinary cytology should be considered if there are risk factors for bladder cancer or if the patient is older than 40 years.
- If there is also proteinuria or renal failure, the patient should be referred to a nephrologist.
- Causes of red discolouration of urine: blood, medication (rifampicin, nitrofurantoin), food (beetroot)
Leukocytes
- Leukocytes (sensitivity about 20 × 106 cells/l, i.e. 2-3 cells / field of view) suggest UTI but there are also other causes, such as chlamydia, tuberculosis, glomerulonephritis.
- Even in the case of infection, the test may remain negative. Plenty of dietary vitamin C will cause false negative results.
Nitrite test
- A positive result means bacterial finding requiring culture.
- Basically, only gram-negative bacteria reduce nitrates to nitrites.
- A negative result will not exclude a UTI with certainty; Staphylococcus saprophyticus and certain enterococci, for example, will not cause a positive reaction.
- The result may also be negative if the bladder time was too short.
- Recurrent cystitis in a healthy adult woman can be treated based on symptoms only, without any tests.
Proteinuria
- The limit of sensitivity to albumin in urine is 0.2 g/l (corresponding to about 0.5 g protein/day).
- Common causes of transient proteinuria include fever, inflammatory diseases and physical exertion. Orthostatic proteinuria should also be kept in mind.
- Positive random finding: repeat dipstick test with morning urine
- If two negative results are obtained from tests done with morning urine, no further investigations are needed.
- If the result is positive or if there is haematuria, investigate more.
- For further investigations, see Proteinuria Proteinuria
- History and clinical examination (auscultation of renal arteries, blood pressure, oedema, tender back or abdomen)
- Quantification of a single sample or collected urine, urine albumin/creatinine ratio (ACR), timed overnight urine collection (minimum 6 hours) for albumin and/or 24-hour urine collection for protein: if the latter exceeds 1 g/day (ACR > 60 mg/mmol), further investigations and follow-up are needed
- Plasma creatinine and eGFR (calculator Gfr Calculator), basic blood count with platelet count, CRP, fasting blood glucose, electrolytes (plasma potassium and sodium), and, as considered necessary, serum protein electrophoresis and free immunoglobulin light chains
- Absence of proteinuria will not exclude severe renal disease.
- Patients with diabetes and other risk groups: measurement of microalbuminuria (ACR or timed overnight urine collection (minimum 6 hours) for albumin)
Other tests
- Glucosuria requires measurement of blood glucose (fasting blood glucose, blood glucose). Use of SGLT2 inhibitors increases glucosuria.
- Ketones (acetoacetic acid, acetone) already become positive after fasting for 12 hours.
- The pH of urine is physiologically between 5 and 9.
- Relative density
- Varies between 1.005 and 1.030, depending on the water balance.
- The relative density of isotonic urine is about 1.010.
- The relative density of morning urine in a healthy adult after refraining overnight from excessive drinking is higher than 1.020.