3.2 Secrets of Urine Testing

Physician's Notebooks 3  - http://physiciansnotebook.blogspot.com - See Homepage Update 22 Dec. 2021

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Chapter 2: Urine Testing

Urine is easy to get and test and tells much. It is made from the blood plasma, with electrolytes and other molecules passing through micro-filters into the kidneys' convoluted tubules, where the water and particles are partly absorbed back into the blood and then re-secreted into the tubules. The final filtrate drains into each kidney’s major drainage tubes, the ureters, which empty on each side into left and right top of the urinary bladder and then the urine is peed out. Your daily state of health - early signs of cancer, infections, metabolic states  - may be seen from your urine, and may predict your kidneys' future function so that renal dialysis may be headed off.

Urine regulates body water, the blood Na⁺, K⁺ and other electrolytes, and the acid-base balance. It gets rid of useless or harmful stuff absorbed from food and drink or breathed from air, and also of products of protein nitrogen, like creatinine and urea.

  Testing starts with looking at urine in morning. If you lay down all night, the first morning urine is best for test because its particles are not so diluted by water you drank.

  Collect morning midstream (right after discarding first bit of stream but also note the starting stream; if it is bloody and clears immediately, it is bleeding from prostate, maybe early sign of cancer.) In clean dry glass inspect it. Delay may cause changes. Fresh morning wake-up urine should be transparent yellow. An amber or brown color may be caused by mild bleeding, or pigment from liver disease or taking vitamin. Fresh small bleeding gives the urine sample an opaque, smoky or hazy look and after minutes the blood cells sediment to bottom of the glass. The color from liver jaundice is deep amber and transparent becoming faint in dilute urine.

   Melanoma cancer pigment is deep brown to black, quite striking. 

   Suddenly peeing deep blue urine any time means someone played a trick by slipping blue dye pill into your food or drink. It is harmless and will go away after 2 hours.

   Fresh urine is normally clear. Urine allowed to stand or if cooled will become cloudy. Freshly passed urine may not smell, but recent food or beverage, especially coffee, toast, alcohol, vitamin pill or fragrant meat may make strong smell. Immediate ammonia smell from freshly voided urine means urinary tract infection but after 10 minutes all urine left standing smells of Ammonia.

Amount of urine in 24 hours: If you measure it, be sure to first completely empty your bladder into toilet at zero time then collect all your urine for exact hours for the test, not forgetting a final bladder emptying collection at the time endpoint. Best to start from AM wake up hour, collecting all urine in screw-top closed jar. The normal 24-hour urine volume is 1 to 2 liters on the usual diet and fluid intake. Below 800 ml (0.8 L) suggests dehydration of low fluid intake or else poor kidney function while more than 2 liters may be due to excess drink or kidney disease.

Specific Gravity (SpG) is a test for the kidneys’ ability to reabsorb water from the renal tubules back into the blood and concentrate the urine. It requires a urine specific gravity float from a medical supply. It measures the effect of antidiuretic hormone (ADH) from pituitary gland. Assuming you do not drink during night, a wake-up specimen of urine should concentrate to SpG 1.015 or higher. Inability to concentrate the urine is sign of poor kidney function but also may be of independent disease of ADH secretion in brain, easily differentiated from weak kidneys by ADH blood test. If SpG is high, a check for protein and glucose should be done because both will raise the SpG without any relation to kidney function.

Dipstick Urine Tester

 Dipstick is strip of chemically treated paper with test bands.

The 6-test shows the WBC  for white blood cells, the Bact for bacteria, the pH measure for acidity-alkalinity, the Glu for glucose, the Alb for albumin a blood protein, and the HGB/RBC for hemoglobin/red blood cell.

Dipstick sells in pharmacy. Depending on area it may need doctor prescription. It comes as screw-top jar of 100 sticks with expiration date stamped on outer box. One person would only rarely use up the sticks before expiration date so better to purchase as a group.

Color changes after touching urine need a seconds timer, a bright light, and a magnifying lens. Remove Dipstick quickly from container, holding the stick at opposite end from test segment. The test is best done in morning, on arising, by urinating directly on the test segment after allowing first stream of urine to go into toilet. Start timing as urine wets Dipstick. Urine may also be tested in clean dry jar, but test immediately.

Warning Interpreting Dipstick: 1) Do not rely on single test result, repeat for abnormal finding; 2) Negative test should not rule-out infection or bleeding or diabetes or kidney damage but it is reassuring you do not have these; 3) Dipstick may mislead due to food, drink or drug that discolors urine, such as red beets or vitamins or body substance produced in illness as in jaundice, melanoma tumor or bleeding into urinary tract or by chemical like ascorbic acid (vitamin C) that interferes with color change.

Urine pH: Urine, several hours after eating, usually gets alkaline (pH 8, the so-called “alkaline tide” but depends on type of food). Fasting more than 24 hours may acidify (pH 5) urine, as will taking vitamin C. Using bicarbonate of soda to neutralize stomach acidity will alkalinize (pH 8) urine. As help in diagnosis, the urine pH should be interpreted with other urine tests. Thus, a urine pH of 5 with urine glucose 4+ means diabetic acidosis while the same pH with negative test for glucose usually comes from fasting or taking a lot of vitamin C. The urine pH is also used to monitor treatment of urinary infection that requires acid urine, usually made by giving vitamin C. The treatment of renal stone condition by taking sodium bicarbonate (baking soda) makes alkaline urine.

Red Blood Cells and Hemoglobin: A dipstick test is useful only when the urine is not obviously bloody. Women during menstruation or shortly after sex will normally test positive for blood. In an attack of severe one-sided flank pain, a Dipstick positive for blood suggests the diagnosis of renal stone passing down urinary tract. The Dipstick test for blood is a good screen for tumors along the urinary tract (kidney, ureter, bladder, prostate, as noted above) because a positive blood Dipstick may be noted intermittently for years before the tumor shows. Also the test is good for monitoring the course of glomerulonephritis (GN; inflammation of kidneys) along with the albumin protein test because continuation of a positive blood may be the only sign of the GN after the acute illness is gone.

Glucose is the 6-carbon sugar that all carbohydrates and many other nutrients get digested or metabolized to. From blood plasma the Glucose passes through kidney filter and is re-absorbed back into blood by cells that line the kidney drainage tubules. But if glucose in blood goes above normal this re-absorption capacity is swamped and excess glucose spills into the urine where it can be measured by change in color in Dipstick GLU segment graded 1+ to 4+. Dipstick positive glucose should suggest diabetes mellitus (DM). A Dipstick GLU 2+ or 4+ means seriously high glucose and the blood should be checked for hyperglycemia (high blood glucose) and the patient for diabetic acidosis. Testing is best done on wake-up morning but – if negative –, also re-test on urine obtained after eating, because a normally negative urine glucose can change to positive from the abnormal glucose spillover after the eating surge in blood glucose.

Albumin protein in urine is easy and useful to test for by Dipstick in range from “trace” (10 mg albumin/deciliter, or dL) to 4+ (500 mg/dL). “No albumin” (0) is normal but “trace” may either be normal response to exercise and erect position or early sign of kidney damage or malfunction. Dipstick albumin test is useful in diagnosis and follow up of kidney disease, and the amount of urine albumin detected is used as monitor of severity & healing and sign of cure. Also it is a good screen to predict and prevent kidneys failure. Here even a developing trace as a consistent new finding can be early warning sign. Especially in a diabetic or hypertensive patient, the constant finding of even a trace of albumin by Dipstick should be worrisome and spark a kidney testing. An albumin 1+ or more should be considered a sign of kidney disease. Recently, special Dipsticks have become available for “micro-albinuria” testing when the usual Dipstick shows “zero” albumin but renal malfunction still suspected. The initial blood test check after finding albumin in urine should be BUN, creatinine and include glucose and glycolated hemoglobin for diabetes mellitus.

White Blood Cell (WBC) test is based on reaction of an enzyme only found in WBC. When present in urine it causes change in color on Dipstick segment from light yellow (negative test) to 3 stages of deepening pink lavender (1+ to 3+). Considering the faintness of the color change and also normally a few WBC are found in urine, only a 2+ to 3+ range of positive should be judged abnormal. Women who test during menses or within the several hours after sex may normally have a positive. A high vitamin C or tetracycline antibiotic in urine inactivates the enzyme and any colored substance ruins the test.

   The aim of the test is to indicate Urinary Tract Infection (UTI). In absence of bleeding in urine, a 3+ WBC alone is interpreted as due to inflammation in the urinary tract. The test should be interpreted with the Bact test segment for bacteria. A positive Bact and a 3+ WBC means bacterial urinary tract infection (UTI) but keep in mind that even with negative Bact test, a 3+ WBC probably is due to a UTI. Also not all UTI's test Dipstick positive for WBC.

   The Bact test for bacteria in urine is based on presence of an enzyme in many Urinary Tract Infection (UTI) bacteria that chemically reduces nitrate (NO3–) to nitrite (NO2–). The Bact test segment is impregnated with colorless nitrate that in positive test turns light pink on reduction by nitrite-forming bacteria after 30 seconds contact with urine. The test limitation is its inability to detect those bacteria that do not have the enzyme so a negative test cannot rule out UTI. More than the other tests, anything that colors urine ruins it. Still, the nitrite test is useful because most of the common UTI bacteria are detected by it but it should be interpreted with the WBC test. A double positive (WBC & Bact nitrite) is significant for UTI. A positive Bact nitrite and a faint or negative WBC means bacteria in urine and no active infection but has high risk to develop UTI and should have culture and sensitivity (bacterial growth and tests against sensitivity to antibiotics) test followed by the best test antibiotic to eradicate the urine bacteria. A double negative is reasonable evidence of no UTI and no bacteria in urine.

Sum-up Dipstick: Dipstick is a good screen for diabetes, kidney disease, infection and renal tract tumor. The hemoglobin and RBC test is useful for quick diagnosis of pain from renal stones (renal colic) and should be part of check for acute abdominal and back pain. And any blood detected in urine should raise red flag for renal tract cancer.

 Urine Sediment: A quick, direct test on urine is to centrifuge a tube of fresh urine and put a smear of the sediment on a glass slide and inspect under microscope for distinctive shaped bodies, bacteria and other micro-organisms. Any bacteria found on fresh urine is abnormal and means infection and may often be diagnosed by distinctive shape or staining. Also special urine sediment bodies tell much about the course of kidney diseases. It is an essential part of all urine tests.  Also as part of the micro sediment test is cytology, which is done by urologists to detect early cancers of the bladder, urethra or prostate.

Endnote: Other body fluids may be tested like urine. Most important is the cerebrospinal fluid obtained by spinal tap (lumbar puncture). This is dealt with Notebooks 9. Also joint fluid, especially from swollen knee joints. And abnormal fluid accumulations in abdomen with liver disease or in lung in heart failure or infections like TB.

END. To read on, click 3.3a Secrets of Blood Testing - Introduction