Blood, protein, leucocytes, nitrites, glucose and ketones
Expansion
| Finding | Significance | Pitfalls |
|---|---|---|
| Blood | Infection, stones, malignancy, glomerulonephritis, trauma | Positive with myoglobin and free haemoglobin; menstruation, exercise |
| Protein | Glomerular disease, infection, heart failure | Detects albumin mainly, so it misses Bence Jones protein; false positive if alkaline or concentrated |
| Leucocytes | Infection, but also sterile pyuria | Poor specificity |
| Nitrites | Gram negative bacteria that reduce nitrate | Negative with Enterococcus, Staphylococcus saprophyticus and Pseudomonas, and with frequent voiding |
| Glucose | Diabetes, SGLT2 inhibitors, pregnancy, renal glycosuria | Not a diagnostic test for diabetes |
| Ketones | Diabetic or alcoholic ketoacidosis, starvation, vomiting | Common and benign in fasting or pregnancy |
Microscopy
- Red cell casts and dysmorphic red cells: glomerulonephritis, and this is the finding that localises bleeding to the glomerulus
- White cell casts: pyelonephritis, interstitial nephritis
- Muddy brown granular casts: acute tubular necrosis
- Hyaline casts: normal, concentrated urine, after exercise
- Crystals: urate, oxalate, cystine
Sterile pyuria, meaning white cells without growth: partially treated infection, tuberculosis, stones, catheters, interstitial nephritis, appendicitis, polycystic disease, and infections not grown on routine culture such as Chlamydia.
Asymptomatic bacteriuria should not be treated except in pregnancy or before urological instrumentation. Treating it in the elderly is a major driver of unnecessary antibiotics, and a positive dipstick in an over-65 with no urinary symptoms does not diagnose a urinary tract infection; in this group the dipstick should generally not be sent at all.
Quantifying proteinuria uses the albumin to creatinine ratio or protein to creatinine ratio on a spot sample, which has replaced 24 hour collection.