Urinalysis Dipstick Components, Additional Substances, and Associated Disorders
The major components measured by urinalysis dipsticks include albumin for protein testing, glucose for glucose testing, acetoacetate for ketone testing, and hemoglobin for blood testing, with each having specific additional substances that can cause true positive results and associated disorders.
Protein Dipstick Test
| Major Component Measured | Additional Components That Can Give a Positive Result | Associated Disorder |
|---|---|---|
| a. Albumin | b. Highly colored urine, protease inhibitors | c. Diabetic nephropathy, chronic kidney disease |
The protein dipstick primarily detects albumin through a pH-based colorimetric reaction. Chemical strip methods for total protein are not sensitive when urine albumin concentration is 20-50 mg/L 1. Standard dipsticks can detect albuminuria above 300 mg/g creatinine, while microalbuminuria dipsticks can detect levels above 30 mg/g creatinine 1.
False positive results can occur with highly colored urine 1. Protease inhibitors added to urine samples may preserve specific proteins and potentially affect dipstick readings 1.
Positive protein dipstick results ≥1+ have a positive predictive value of 91% for albumin:creatinine ratios ≥30 μg/mg, making them useful for screening diabetic nephropathy 2. However, the American Diabetes Association recommends confirming positive results with quantitative laboratory testing 1.
Glucose Dipstick Test
| Major Component Measured | Additional Components That Can Give a Positive Result | Associated Disorder |
|---|---|---|
| d. Glucose | e. None significant | f. Diabetes mellitus |
Urinary glucose testing uses an enzymatic reaction specific to glucose. The American Diabetes Association recommends self-monitoring of blood glucose over urine glucose testing due to limitations of urine testing 3. Urine glucose reflects average blood glucose since the last void rather than current levels and is affected by hydration status and renal threshold variations 3.
Dipstick urinalysis for glucose has high sensitivity (100%) and specificity (98.5%) for detecting diabetes mellitus 4. Post-mortem studies show good sensitivity (0.83) and specificity (0.93) for detecting hyperglycemia 5.
Ketone Dipstick Test
| Major Component Measured | Additional Components That Can Give a Positive Result | Associated Disorder |
|---|---|---|
| g. Acetoacetate | h. Acetone, captopril and other sulfhydryl drugs | i. Diabetic ketoacidosis, alcoholic ketoacidosis, starvation |
Ketone dipsticks use the nitroprusside reaction to detect acetoacetate, resulting in a purple color 1. If the reagent contains glycine, acetone is also measured, but the reagent is much more sensitive to acetoacetate than acetone 1.
Importantly, nitroprusside-based dipsticks do not detect beta-hydroxybutyrate (βOHB), which is the predominant ketone body in diabetic ketoacidosis (DKA) 1, 3. False positive results can occur with certain sulfhydryl drugs like captopril, and false negative readings with aged test strips or highly acidic urine 3.
Despite these limitations, urine ketone testing has high sensitivity and negative predictive value for excluding DKA in hyperglycemic patients 3. Positive urine ketone readings are found in up to 30% of first morning urine specimens from pregnant women (with or without diabetes), during starvation, and after hypoglycemia 1.
Blood Dipstick Test
| Major Component Measured | Additional Components That Can Give a Positive Result | Associated Disorder |
|---|---|---|
| j. Hemoglobin | k. Myoglobin, microbial peroxidases | l. Urinary tract infection, glomerulonephritis |
The blood dipstick primarily detects hemoglobin through its peroxidase-like activity. Myoglobin can also cause positive results due to similar peroxidase activity. Certain microbial peroxidases can potentially cause false positive results.
Any degree of blood contamination can affect dipstick analysis results, with effects depending on urine color and the variable measured 6. Blood contamination can significantly affect other dipstick parameters including bilirubin, ketones, pH, and specific gravity 6.
Microscopic blood contamination may affect urine protein-to-creatinine ratio; thus, blood contamination should be considered as a differential diagnosis for proteinuria in yellow urine samples 6.
Important Clinical Considerations
Dipstick urinalysis serves as a rapid quality control by measuring urine pH and various contents, but there is no consensus on which dipstick test is most suitable for inclusion/exclusion criteria in studies 1.
For diabetic patients, blood ketone testing that quantifies β-hydroxybutyrate is preferred for diagnosing and monitoring ketoacidosis 3.
Users of SGLT2 inhibitors should measure ketones at any sign of illness, regardless of glucose levels, due to the risk of euglycemic ketoacidosis 3.
Positive urine albumin screening results by semiquantitative tests should be confirmed by quantitative analysis in an accredited laboratory 1.