Nephro- Lab studies

What does the evaluation of all patients for suspected renal disease include at minimum?

H&P, UA w/ dipstick & microscopic analysis, assessment of GFR

What is the principal end product of protein catabolism synthesized in the liver, constitutes one half of total urinary solids, & is excreted by GFR?

Urea

What is the serum marker of urea level?

BUN

How does the steady states of Urea & Creatinine compare to GFR?

Inverse

What is the normal value for BUN?

8-20 mg/dl (10 average)

When is BUN increased?

Acute and chronic renal failure & urinary obstruction

Would the following increase or decrease BUN?

• Dehydration, reduced renal perfusion (CHF, hypovolemia), increased dietary protein

• Accelerated catabolism (fever, trauma, GI bleeding)

• Steroids, tetracyclines

Increase

Would the following increase or decrease BUN?

• Overhydration

• increased renal perfusion (pregnancy, SIADH)

• restriction of dietary protein/malnutrition

• liver disease

Decrease

What is a product of muscle metabolism produced at a relatively constant rate & cleared by renal excretion, is freely filterable by the glomerulus & not reabsorbed/secreted by the renal tubules?

Creatinine

What is the usual means of estimating GFR?

Creatinine clearance

What is the normal value for creatinine?

0.6 - 1.2 mg/dl (1 average)

What is the BUN/Cr ratio normally?

10:1

______may overestimate GFR ; _______ may underestimate GFR

Cr clearance ; BUN

When trying to determine Cr clearance, what should be used if a 24 hr urine can’t be collected?

Cockcroft and Gault method → serum only, based on pts age, sex & wt

What is the Cockcroft & Gault formula?

C_cr = (140 - age) x Weight (kg) / P_cr x 72

What stage of CKD?

• kidney damage, protein in urine, normal filtration rate

• GFR > 90

Stage 1

What stage of CKD?

• Kidney damage, mild dec in rate

• GFR 60-89

Stage 2

What stage of CKD?

• moderate dec in rate

• GFR 30-59

Stage 3

What stage of CKD?

• Severe decline in rate

• GFR 15-29

Stage 4

What stage of CKD?

• Kidney failure

• GFR < 15

Stage 5

What sample is preferred for urinalysis?

Clean catch midstream

What is best for UA microscopy?

First morning void

How soon should a UA be tested?

Within an hour or needs to be refrigerated

What UA is best for a true quantitative evaluation?

24 hr volume

What correlates well with urine osmolality & gives important insight into hydration status and concentrating ability of kidneys?

Specific gravity

What is the normal range of specific gravity (SG)?

1.010 (1.003-1.030)

What is useful for the diagnosis of UTIs, urinary stone disease, and RTA?

Urinary pH

What is the normal urinary pH range?

5.0-8.0

What is often the first indication of renal disease?

Proteinuria

How is protein scored in urinalysis?

Negative to 4+

What protein is a dipstick most sensitive to?

Albumin

What is the normal level of urobilinogen?

1-4 mg/day

What might lead to increased urobilinogen levels?

Hemolytic processes or hepatic dz

What is the normal amount of bilirubin in urine?

None (if positive, implies increased serum levels)

What is a normal UA glucose?

Negative (< 0.1% filtered by glomerulus appears in urine)

What should be done if urine glucose is positive?

Screen for DM

What is useful to screen for ketosis & DKA?

Ketones

What is the normal level of ketones detected in urine?

None

What might cause false positives urine ketones?

Fasting, pregnancy, post exercise

What is a normal urine nitrite level on dipstick?

None

What is an indicator for bacteriuria?

Nitrites (G- bacteria reduces nitrate to nitrite)

What should you think of with positive urine nitrite?

Bacterial infection

What sample is most reliable when testing for urine nitrites?

First morning void

What is an enzyme produced by neutrophils & is suggestive of bacteria if positive on urine dipstick?

Leukocyte esterase

What part of the dipstick urinalysis measures intact erythrocytes, free hgb, & myoglobin and should be confirmed with microscopy if positive?

Blood

What is the MC excreted protein in urine & is benign?

Tamm-horsfall mucoprotein / uromodulin

Excretion of what glycoprotein in urine may provide defense against UTIs & also may act as constitutive inhibitor of calcium crystallization in renal fluids?

Uromodulin

What is helpful in showing evidence of renal dz vs lower UTI & in indicating the type and activity of renal or systemic condition (must examine atlas 10 HPF for dx)?

Microscopic urinalysis

What is the presence of > 5 leukocytes per high power field on microscopic UA considered?

Significant pyuria

What in urine is indicative of injury to the urinary tract, that may or may not be due to infection?

Leukocytes

The presence of > 3 erythrocytes per high power field is considered what?

Significant, warrants further evaluation

What do dysmorphic (irregularly shaped) RBCs on microscopic UA indicate?

GN

What do round/normal erythrocytes on microscopic UA indicate?

Dz along epithelial lining of tract

What does the presence of squamous epithelial cells on microscopic UA indicate?

Contamination → repeat collection & test

What is indicated if large numbers of clumps of transitional epithelial cells is present on microscopic UA?

Possible neoplasm

What is the MC yeast seen in the urine, typically budding & clumps observed?

Candida albicans

How is trichomonas identified in urine?

Pear shape & flagella

Where are casts formed?

Distal tubules & collecting ducts (named based on shape/origin)

What cast is characteristic of pyelonephritis & may also be seen in interstitial nephritis?

White cell cast

What cast indicates intraparenchymal bleeding and is hallmark of GN?

Red cell casts

What cast is seen concentrated in urine, febrile dz, following strenuous exercise, during course of diuretic therapy, and is not specific for renal disease?

Hyaline casts

What casts consist of dense accumulation of sloughed tubular cells, characteristically seen in acute tubular necrosis?

Tubular cell casts

What casts consist of finely or coarsely granular material, is non specific but usually pathologic & seen in ATN, GN, or tubulointerstitial dz?

Granular casts

What casts form in tubules that have become dilated and atrophic d/t chronic parenchymal dz & is frequently seen in CRF?

Broad waxy casts