Proximal Information and Courses from MediaLab, Inc.

In the healthy individual, almost all of the glucose filtered by the renal glomerulus is reabsorbed in the proximal convoluted tubule. The amount of glucose reabsorbed by the proximal tubule is determined by the body's need to maintain a sufficient level of glucose in the blood. If the concentration of blood glucose becomes too high (160-180 mg/dL), the tubules no longer reabsorb glucose, allowing it to pass through into the urine. It is important to note that glucose may appear in the urine of healthy individuals after consuming a meal that is high in glucose. Fasting prior to providing a sample for screening eliminates this problem.

The typical daily diet of most Americans contains approximately 10 to 15 mg of iron. Sources of dietary iron include heme iron from meats and nonheme iron from whole grains and vegetables. Many processed foods, such as breakfast cereal, are fortified with iron. However, the normal individual absorbs only 5% to 15% of dietary iron, or about 1 to 2 mg daily. Females may absorb slightly more iron than males as they require more iron to replace that lost through menstruation and to meet the increased need for iron in pregnancy.Absorption of iron occurs through the mucosal cells in the duodenum (proximal small intestine). Dietary iron that is not absorbed is excreted in the feces. Intestinal absorption provides the means for regulating the amount of iron in the body.The amount of Iron absorbed is normally low because iron is well conserved within the body. Heme iron from senescent erythrocytes is cycled back into the iron pool and reused for incorporation into developing erythrocytes. Furthermore, iron is normally lost from the body only in very small amounts, primarily through desquamation of mucosal cells in the gastrointestinal tract and losses through body secretions, including urine, sweat and feces. Therefore, under normal conditions, very little dietary iron needs to be absorbed to maintain iron homeostasis.(3)

Blood that is drawn from a vein that has an intravenous (IV) line may be diluted by the IV fluid. This can ultimately affect the accuracy of the blood test results. Therefore, an arm containing an IV should not be used to draw blood specimens if it can be avoided. However, if there is no alternative and an arm with an IV line in place must be used for venipuncture, try to choose a site away from and below the location of the IV. Document that the venipuncture was performed distal to (below) an infusion site. If the only vein available is proximal to (above and near) the IV, these steps should be followed: Ask the patient's caregiver if the IV can be turned off for a short period of time. The IV should be discontinued for at least two minutes before the venipuncture. Apply the tourniquet between the IV site and the area of the venipuncture. Perform the venipuncture. Document that the venipuncture was performed proximal to an IV site and that the IV was discontinued for two minutes prior to specimen collection. Notify the patient's caregiver when the procedure is completed and be certain that she/he restarts the IV.

Fructose makes up 99% of the reducing sugar present in semen. This sugar is produced in the seminal vesicles and its absence may indicate an obstruction proximal to these glands. Although a fructose test is NOT part of a routine semen analysis, the clinician may want to measure this in cases of azoospermia. In azoospermia secondary to obstruction of the ejaculatory ducts or absence of the vas deferens, fructose is usually absent. When azoospermia is caused by failure of the testes to produce sperm, fructose is present. Measuring fructose levels can thus help the clinician determine the cause of azoospermia, although measurement of pH is often more useful in this regard. The procedure for determining the amount of fructose in semen involves heating semen in a strong acid in the presence of resorcinol. Fructose gives a red color to this solution when present.

Renal epithelial fragments of collecting duct origin are composed of three or more cuboidal cells. These fragments indicate a more severe form of renal tubule injury with basement membrane disruption. Proximal and distal convoluted tubule renal epithelial cells are not found in fragment form. In addition to the indication of severe tubule damage, proper identification of these fragments is important to avoid a false positive diagnosis of low-grade transitional cell carcinoma. Transitional cell carcinoma is a type of cancer seen in 71% of cases of malignant tumors of the ureter.