Chapter 9: Nephrology

Produced in skeletal muscle metabolism and filtered by the kidney

Elevated in renal dysfunction

Higher in muscular people and lower in elderly patients and pregnant women

Can be elevated by medications such as ACEIs, ARBs, cimetidine, trimethoprim, aminoglycosides

First step in evaluating kidney disease

Monitor kidney function

Used in determination of BUN:Cr ratio, fractional excretion of sodium or urea

Produced by the liver during the urea cycle and filtered by the kidneys

Elevated in renal dysfunction

Can be elevated in patients who are bleeding, taking prednisone, and who are dehydrated

First step in evaluating kidney disease, along with serum Cr

BUN:Cr ratio can be used to determine kidney function

UA

Random specimen, midstream collection (“clean catch”), first morning collection, bladder catheterization

Dipstick testing: specific gravity, pH, protein, hemoglobin, glucose, ketones, bilirubin, nitrite, leukocyte esterase

Microscopy: crystals, cells, casts, infecting organisms, and oval fatty bodies

First test + serum Cr in patients with kidney disease

Screening in patients with family history of kidney disease

To detect infection, dehydration, diabetic ketoacidosis, proteinuria, hematuria, rhabodmyolysis, nephrolithasis

Urine culture

Midstream clean catch, bladder catheterization, suprapubic aspiration

>100,000 colony-forming units/mL of one type of bacteria indicates infection in a midstream, clean catch specimen

Growth of several types of bacteria indicates contamination

Susceptibility testing may guide antibiotic therapy

Infection

Usually ordered with UA

Quantitative testing for proteinuria (such as orthostatic proteinuria)

Kidney function monitoring for patients with known kidney disease

Early detection of kidney damage in the form of proteinuria

Other conditions: Diabetic nephropathy, preeclampsia, nephrotic syndrome, multiple myeloma

>3.5 g considered nephrotic range proteinuria

<0.2 is normal

>0.3 g/24 hr or >0.3 protein to Cr ratio in preeclampsia

Hydronephrosis (Figure 9.1), renal failure of unknown etiology, renal abscess, urinary calculus

Identifying and characterizing renal cysts or masses

Part of evaluation of malignancy in patients >50 years of age with hematuria

Localizing kidney for percutaneous procedures

Renal artery stenosis, ...