CHAPTER 14- RENAL PHYSIOLOGY AND URINALYSIS
Urinalysis is thephysical, chemical, and microscopic analysis of urine. It providesinformation that reflects a patient’s general health as well asclinical picture of the patient and potential disease.
Qualityassessment program ensures that results of testing are meaningful
Elements ofquality assessment include record keeping, procedure manual,materials and equipment, proficiency testing, and continuingeducation and training.
To aid in the diagnosis of disease
To monitor wellness (screening for congenital or hereditary disease)
To monitor therapy (effectiveness or complications)
Control specimensare tested as follows:
Test all opened bottles of reagent strips each morning
Test each new bottle on opening
Record data on the record sheet daily
Urine isconsidered a fluid composed of the blood’s waste materials. It isformed in the kidney and excreted through the urinary system.
Urinary systemconsists of
Blood enters thekidney through the renal artery and leaves the glomerulus through theefferent arterioles. One fourth of the cardiac output is containedwithin the kidneys at a given time.
The kidneys arebean-shaped, reddish organs with each weighing about 150 g.
Hilum- anindentation through which the renal vessels, nerves, lymphatics, andrenal pelvis enter or leave the renal sinus.
Renal sinus- thespace enclosed by the renal parenchyma.
Cortex-continuous subscapular band of tissue
The medullaconsists of triangular structures called pyramids with tips referredto as papillae.
The functionalunit of the kidney is called the nephron. The formed urine leavesthrough the ureter for temporary storage in the bladder. Eventually,it is eliminated through the urethra
Functions of thekidney (Those that occur through filtration, absorption, andsecretion):
Removal of nitrogenous wastes from acids and protein metabolism
Retention of nutrients such as water, proteins, glucose, and electrolytes
Water and electrolyte balance
Hormone synthesis, such as vitamin D, renin, and erythropoietin
Glomerulus(working portion of the kidney) refers to a tuft of anastomosingcapillaries. Urine formation begins in the glomerulus through thestructure that delivers blood to the nephron. Blood that circulatesthrough the glomerulus is filtered into the Bowman’s capsule.
Glomerularfiltrate refers to the blood plasma without fats and proteins. It isan ultrafiltrate of blood. It is called iso-osmolar with plasma sinceit has the most solutes of plasma. Although 180 L of glomerularfiltrate are produced daily, only 1 or 2 L of urine are eliminatedfrom the body.
Reabsorption ofabout 80% of the fluid and electrolytes filtered by the glomerulusoccurs in the proximal convoluted tubule.
Activereabsorption refers to the movement of the analyte against theconcentration gradient while passive reabsorption involves movementalong the concentration gradient.
Water, chloride,bicarbonate, potassium ions, and 40-50% of the urea are passivelyreabsorbed. On the other hand, sodium ions, glucose, protein, aminoacids, uric acid, calcium, potassium, magnesium, and phosphate areactively reabsorbed.
Renal plasmathreshold refers to the maximum amount of an analyte that will becompletely reabsorbed from the glomerular filtrate.
The descendingand ascending loops of Henle function to reduce the volume of theurine while reabsorbing or recovering sodium and chloride. Thedescending portion is the concentrating segment while the ascendingloop is the diluting segment.
The hormonealdosterone controls the sodium-potassium pump.
Water isreabsorbed under the influence of the anti-diuretic hormone.
The cells liningthe urinary system are classified as renal, transitional, or squamousepithelial cells.
The compositionof urine depends on factors such as diet, metabolic rate, generalstate of the body, nutritional status, and state of the kidney.
Urine consists of96% water and 4% dissolved substances such as salt, urea, uric acid,and creatinine. However, the amount of creatinine excreted depends onthe body’s muscle mass rather than diet. The levels of thesedissolved substances are higher in urine than in other body fluids.
Indication of thestate of the kidney/Urinary tract:
Indicators ofmetabolic and other conditions:
glucose and ketones
Indicators ofother systemic (nonrenal) conditions or disease
Advantages to dryreagent tests over traditional tests
Relative ease in learning to use
Smaller sample volumes required
The pH is theunit that describes the acidity or alkalinity of a solution.
Proteinuria isthe occurrence of protein in urine. It may occur due to glomerulardamage, tubular damage, pre-renal disorders, lower urinary tractdisorders, and asymptomatic disorders.
Hematuria is thepresence of red blood cells in urine. It may occur due to kidneylesions or bleeding in the urinary tract. It may show kidney orbladder tumor, kidney stones, glomerular damage, cystitis, orinterstitial nephritis. On the other hand, hemoglobinuria is thepresence of free hemoglobin in the urine. It occurs due to hemolysisin the bloodstream.
Myoglobinuria isthe presence of myoglobin in urine. It could result from traumaticmuscle injury, excessive exercise, or crush injuries.
Tests for thepresence of nitrite in urine are used to detect the presence ofurinary tract infections.
Ketone bodiesrefer to acetone, acetoacetic acid, and β-hydroxybutyric acid.Ketosis is the combination of increased ketones in the urine andblood.
Tests for urinebilirubin and urobilinogen are used as indicators of liver function.
Factors that mustbe standardized according to CLSI guidelines:
Time of centrifugation
Speed of centrifugation
Concentration factor of the sediment
Volume of the sediment examined
Constituents ofurine sediment:
Biological (organized sediment) – RBCs, WBCs, epithelial cells, bacteria, yeast, casts, fungi, parasites and spermatozoa
Chemical (unorganized sediment) – crystals of chemicals and amorphous material
Casts areclassified into hyaline, cellular (WBC, RBC, bacterial, epithelial),granular, waxy, fatty, pigmented (bilirubin, drug pigment, myoglobin,hemoglobin), and inclusion casts (hemosiderin, crystal).
Crystals found inurine sediment
Normal acid crystals – uric acid, acid urates, monosodium or sodium urates
Normal alkaline crystals – calcium carbonate, triple phosphates
Abnormal crystals of metabolic origin – tyrosine, leucine, cholesterol
Abnormal crystals of istrogenic origin (drugs) – sulfonamides, ampicillin, acyclovir
Contaminants andartifacts in urine sediment
Fibers (including disposable and diaper fibers)
CHAPTER 15-EXAMINATION OF BODY FLUIDS AND MISCELLANEOUS SPECIMENS
RoutineExamination of Cerebrospinal fluid
Slight hazinessin the specimen or turbidity may indicate an increased white bloodcell count. Turbidity in the spinal fluid may result from thepresence of large numbers of leucocytes or from bacteria, increaseprotein, or lipid. If radiographic contrast media have been injected,the cerebrospinal fluid (CSF) will appear oily, and when mixed,turbid
CSF should alsobe examined for clotting. Clotting may occur from increasedfibrinogen resulting from a traumatic tap (inclusion of blood in thespecimen from the lumbar puncture). Furthermore, clotting may beassociated with subarachnoid block or meningitis.
In addition,bloody fluid may result from traumatic tap or from subarachnoidhemorrhage. If the blood results from the latter, then the color ofthe fluid will look the same in all the collection tubes. However, ifthe blood results from a traumatic tap, then successive collection oftubes will show less bloody fluid.
Xanthochromiarefers to the presence of a pale-pink to pale-orange or yellow colorin the supernatant CSF. It occurs due to the release of hemoglobinfrom hemolyzed red blood cells, which begins a few hours afterhemorrhage. Yellow xanthochromia will result when the hemorrhage isold. Besides, subarachnoid bleeding is associated with themicroscopic observation of crythrophagia. The latter term describesthe ingestion of RBCs by macrophages in the CSF.
Normally, thereare no RBCs in CSF. The normal WBC count in CSF is 0-8 cells/µL.Therefore, more than 10 cells/µL is considered abnormal. Increasedcounts of WBCs are observed in noninfectious conditions (multiplesclerosis and trauma) and infectious diseases (meningitis).
Cytocentrifugation – provides better cell yield and morphologic preservation than ordinary centrifugation
Smears from centrifuged spinal fluid sediment – relatively poor recovery of cells, damaged/distorted cells
Other concentration techniques – time-consuming and expensive, require more technical expertise
Differential cell count – exactly 100 WBCs are counted and classified
Gram’s stainand culture are done. The former test is most useful in diagnosis ofacute bacterial meningitis because the organisms can be seen in theGram-stained specimen.
Such examinationsinclude the Venereal Disease Research Laboratories (VDRL) test andthe fluorescent treponemal antibody absorption (FTA-ABS) test. Inparticular, the VDRL test is used for syphilis.
Serous fluidshave a similar concentration to serum. They are contained within theclosed cavities of the body. These cavities are lined by a serousmembrane composed of a double layer of mesothelial cells. Theyinclude the peritoneal, pericardial, and pleural cavities.
An increasedvolume of serous fluids is referred to as an effusion.
Transudates referto the normal serous fluids that are formed as an ultrafiltrate ofplasma as it filters through the capillary endothelium. On the otherhand, exudates refer to effusions that result from an inflammatoryresponse to conditions that directly affect the serous cavity.
Pleural fluid(1-10 mL) surrounds the lungs and lines the walls of the thoracicactivity.
Pericardial fluid(25-50 mL) forms continually in the space enclosing the heart.
Turgeon, M. L. (2007). Linne & Ringsrud`s Clinical LaboratoryScience: The Basics and Routine Techniques (5th ed.).St. Louis, Mo.: Mosby Elsevier.