Urine and Urinalysis

Properties of Urine

Many of us have had a urinalysis done for a variety of reasons.  Let’s start with the last three things in this table.  Urine is yellow form the pigment urochrome.  This yellow is created from the breakdown of hemoglobinThe oxygen-carrying protein in red blood cells that gives blood its red color..  Can your urineThe liquid waste excreted by the kidneys. be other colors?  Sure.  Should your urine be other colors?  Probably not. 

Many prescription drugs and metabolic diseases can change the color of your urine and stool.  In general, your urine should be on the clear side.  Cloudy urine usually results from the activity of bacteria, suggesting a urinary tract infection or UTI.  Leukocyte esterase is a product of white blood cellsThe basic structural and functional units of life.. It acts on an infection in your urine. This supports the visual observation of cloudiness as an indicator of an infection.  When WBCs are present in urine, it is called pyuria.

I once read somewhere that urine should small “floral.”  I think I might disagree with that.  Urine has an odor due mostly to the nitrogenous wastesMetabolic waste products like urea, creatinine, and uric acid, excreted by the kidneys..  However, as urine stands, bacteria convert the urea to ammonia and starts to smell like ammonia.

Urine Solutes

An urinalysis includes a few measurements. These measurements can give you an idea of the level of solutes in your urine. The deeper the yellow, the more solutes.  That visual observation can be backed up by two test results: the specific gravityA measure of urine concentration that compares the density of urine to water. and the osmolarityA measure of solute concentration in fluid; affects fluid movement between compartments..  Specific gravity is a ratio of the density of your urine to the density of distilled waterThe universal solvent essential for life..  When urine is very dilute, the specific gravity is low, more like the specific gravity of distilled water.  When specific gravity is high, there are more solutes present.  Osmolarity also supports visual observations and specific gravity as to the solute amount in the urine.  Osmolarity is the ration of the amount of solutes to the amount of water.  When someone is dehydrated, their urine’s osmolarity will be high.

Plasma vs. Urine

This is a great table.  Well, I think so.  This table compares the values of plasmaThe liquid component of blood. to the values of things in urine.  Let’s first look at those ionsCharged atoms or molecules..  Sodium in urine can range widely, from 40 to 220 milliequivalents per liter. This range helps control the tighter range of 135 to 145 found in plasma.  Opposite to this is potassium(K⁺): Major ICF cation; essential for muscle and nerve function..  There is lots of potassium in urine and a wide range of it possible too.  But, look at the range of potassium in blood.  That 3.5 to 5.0 milliequivalents per liter is so small compared to the 25-100 that can be found in urine.  Same for bicarbonate(HCO₃⁻) – A crucial buffer in blood that helps maintain pH balance; formed when carbon dioxide, lots in the plasma, not a lot in the urine.  We are always ALWAYS making hydrogen cations(H⁺): Protons that influence pH levels in body fluids. all day and we always need bicarbonate. 

At the bottom of this table are the various forms of nitrogenous wastes that can be found in urine.  Remember that nitrogenous wastes compare primarily from the metabolismThe sum of all chemical reactions in the body. of proteinsLarge molecules made of amino acids with various functions in the body..  Look at how high they are in the urine compared to the ranges in blood.  Urea is astounding at 1800 milliequivalents per liter compared to the 8-25 that can be in blood.  Creatinine is a nitrogenous waste product we can use for renal clearance, discussed in another minilecture. 

Uric acidA substance that releases hydrogen ions (H⁺) in solution. is the primary contributor of gout or gouty arthritis.  In this condition, uric acid is not excreted adequately. This leads to a buildup in articulations. It affects areas especially in the lower limbs, such as knees, ankles, and the knuckle of the big toe.  I once saw a commercial for a drug for gout. It depicted people walking around carrying a big jug of uric acid.  That’s a pretty accurate depiction of what gout really is!

What SHOULDN’T Be in Urine

The filtrationThe process by which fluid moves out of capillaries into surrounding tissues due to hydrostatic pre membrane is the combination of podocytesSpecialized cells in the glomerulus that form filtration slits, preventing large molecules from ente and the fenestrated capillaryCapillaries with pores (fenestrations) that allow rapid exchange of fluids and small solutes (found of the glomerulusA network of capillaries in the nephron where blood filtration occurs.. It prevents red blood cells from escaping into urine.  Usually, when there is blood in urine, it is called hematuria. It consists of fragments of red blood cells rather than full red blood cells.  Hemolytic anemiaA condition characterized by a deficiency of red blood cells or hemoglobin, leading to reduced oxyge is an autoimmune disease. In this condition, red blood cells are broken down prematurely in circulation. Normally, they are broken down in the spleen.  This leaves those fragments in the urine.

Your body is waiting for the next famine.  No, really, the human race has been subjected to famine for its entirety.  You might be like, “That’s not what it looks like when I go grocery shopping.”  Yeah, here, but in other parts of the world, famine is a guarantee.  That being said, your urine should never contain things that could be converted into ATPThe energy currency of cells used for muscle contraction..  Glucose should not be in your urine unless you ate an entire cheesecake.  If glucoseA simple sugar that is the main source of energy for cells. is present in urine, we call it glycosuria. 

Lipids shouldn’t be in your urine, but what does end up in urine are ketone bodies.  Ketones are the result from metabolism of triglycerides.  The keto-diet focuses on shifting your body’s metabolism from carbohydrateOrganic molecules composed of carbon, hydrogen, and oxygen, primarily used for energy. seeking to lipid seeking.  However, if too many ketones are created, they will spill over into the urine, creating ketonuria.  Fruity smelling breath accompanies this. 

Proteins smaller than albuminA plasma protein that helps maintain osmotic pressure and transport substances. and some amino acids are excreted in urine, but at a very very low rate.

Urine Volume

You probably make about 1-2 liters of urine a day.  Think about a liter soda bottle.  I read in your book that some medications and diseases can cause an increase in urine production. You can produce up to 20 liters per day of urine.  If I took one of those drugs, I’d never be able to get through a 50 minute session of class! 

I just have some terms here that apply to urine volume.  Polyuria is more than 2 liters per day of urine.  Oliguria is less than half a liter of urine per day and anuria is no urine.  At 400 mL per day, you are not excreting nitrogenous wastes.  This volume is a little less than half a liter.  In the case study on renal failure, our patient had oliguria.  We were giving him water. It was just going to the interstitial fluids in his body. This caused some pretty hefty edemaExcess fluid in interstitial spaces..

If you drink more fluids or if your blood pressureThe force exerted by gases in the respiratory system, affecting airflow and gas exchange. rises, your urine output will increase.  If you are making angiotensin IIA powerful vasoconstrictor that increases blood pressure and stimulates aldosterone release., aldosteroneA hormone that increases sodium and water reabsorption in the kidneys, helping regulate blood pressu, or ADH, your urine volume will decrease.  Remember, I’m talking about volume of urine, not what’s in it.