Nephro Study Guide

What simple, noninvasive, cheap & safe imaging study can identify thickness, kidney size & check for symmetry?

US

What does a kidney length < 9 cm on US indicate?

Irreversible renal dz

What are indications for renal US?

Hydropnephrosis, cysts, obstruction, ADPKD screening, characterize renal masses, localize kidney for bx, & assess post voiding residual urine volume of bladder

What is required for further investigation of abnormalities detected by US or IVP?

CT

When is contrast not needed with CT?

Hemorrhage or stone evaluation

What is 95% sensitive and 98% specific in detecting renal stones in a patient presenting with acute flank pain?

Noncontrast helical CT

What are indications for renal CT?

Solid or cystic lesions, definitive role in staging renal neoplasms & imaging kidneys following trauma

What is a combo of IVP and abd CT that offers increased parenchymal resolution & is useful for hematuria w/up, especially if suspecting renal cancer?

CT urogram (CTU)

What is the normal value for BUN?

10 mg/dL

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 the usual means of estimating GFR?

Creatinine clearance

What should be used when serum creatinine is not helpful?

Cystatin C

What is the normal value for creatinine?

1.0 mg/dL

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 & 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

*multiply by 0.85 for females

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 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

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

What protein is a dipstick most sensitive to?

Albumin

What might lead to increased urobilinogen levels (> 1-4 mg/day)?

Hemolytic processes or hepatic dz

What is the normal amount of bilirubin in urine?

None (if positive, implies increased serum levels)

What should be done if glucose is positive on urine dipstick?

Screen for DM

What on UA is useful to screen for ketosis & DKA?

Ketones

*Fasting, pregnancy, & exercise can cause false positives

What would positive nitrites on UA indicate?

Bacteriuria (G- bacteria reduces nitrate to nitrite)

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, & protects against UTIs and calcium crystallization in renal fluids?

Tamm-horsfall mucoprotein / uromodulin

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

Significant pyuria

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

Tubular cell 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

What are the major cellular osmoles?

Na+ >> glucose > urea

What is the formula for osmolality gap?

measured osm - calculated osm

How do you calculate serum osmolarity?

2(Na) + Glucose/18 + BUN/2.8

What is the normal range for osmolal gap (OG)?

+10 to -10

What OG value is considered critical or cutoff?

> 15

What does the presence of low blood pH, elevated anion gap, & greatly elevated OG indicate?

Medical emergency requires prompt treatment

What is the major cation of ECF that is regulated by the kidneys (ADH & aldosterone), & increases blood pressure?

Na

How does aldosterone affect Na?

Na retaining; increases Na & water with K loss

What serum Na level indicates hyponatremia?

< 135 mEq/L

At what serum Na level are moderate to severe symptoms seen (N, generalized weakness, confusion, seizures)?

< 120 mEq/L

What type of hyponatremic state is characterized by:

• Decreased total body water (TBW)

• Decreased total body Na to a greater extent

• Decreased ECF volume

Hypovolemic hyponatremia

What type of hyponatremic state is characterized by:

• Increased TBW

• Normal total body Na

• Minimally-moderately increased ECF volume w/o edema

Euvolemic hyponatremia

What type of hyponatremic state is characterized by:

• Increased TBW to a greater extent

• Increased total body Na

• Markedly increased ECF volume with edema

Hypervolemic hyponatremia

What type of hyponatremic state is characterized by:

• Water shifts from intracellular to extracellular compartment → dilution of Na

• TBW & total body Na unchanged

• occurs with hyperglycemia or mannitol administration

Redistributive hyponatremia

What type of hyponatremic state is characterized by:

• Aqueous phase is diluted by excessive sugars, proteins, or lipids

• TBW & total body Na are unchanged

• seen with hypertriglyceridemia & MM

Pseudohyponatremia

What causes euvolemic or normovolemic hyponatremia?

Early SIADH, polydipsia, diuretics, hypothyroidism, severe hyperglycemia (polyuria)

How should pseudohyponatremia be corrected for hyperglycemia to get the true value of sodium?

Add 1.6 to the Na for every 100 mg/dL increment the glucose is over 100

**sweet 16 rule

What clinical syndrome of non-osmotic release or enhancement of ADH action (excess ADH) leads to pathological H2O retention, hyponatremia, cerebral edema, & neurological dysfunction?

Syndrome of inappropriate ADH (SIADH)

What are non osmotic releasers or enhancers of ADH that cause hyponatremia?

N +/- V, pain, lymphomas, leukemias, cancers, cirrhosis

Drugs: lithium, SSRIs, ecstasy, cytotoxin, narcotics

What kind of hyponatremia is dehydration with both sodium and water losses?

Hypovolemic hyponatremia

What causes hypovolemic hyponatremia?

Loss of fluid (GI, burns), hypotonic fluid replacement, thiazide diuretics (Na & K loss), K depletion in cells (Na move into cells), aldosterone deficiency (inc Na & H2O loss)

What causes hypervolemic hyponatremia?

CHF, hepatic cirrhosis, over hydration, nephrotic syndrome, renal failure

What serum Na level is defined as hypernatremia?

> 145 mEq/l

What is the major defense against the development of hypernatremia?

Thirst

What symptoms are associated with hypernatremia?

Tremors, irritability, ataxia, confusion, coma

What is the MCC of hypernatremia?

Hypovolemic hypernatremia (caused by dehydration, V, or D)

What causes normovolemic hypernatremia?

Insensible losses (skin/stool/lung; ≥500 cc/day), polyuria (DI)

Will DI or DM have hypernatremia?

DI

Will DI or DM have pseudohyponatremia?

DM

What causes hypervolemic hypernatremia?

Hypertonic saline, sodium bicarb, hyperaldosteronism, cushing’s syndrome

What condition is characterized by increased thirst, hypernatremia, and loss of large volumes of urine (low SG) due to loss of ADH production or function?

Diabetes insipidus (DI)

What are ssx of DI?

Polydipsia & polyuria

How is DI diagnosed?

Measure ADH level & vasopressin challenge test

What is the treatment for DI?

Replete ADH or HCTZ, & indocin

What condition?

• absence or deficiency of ADH from the posterior pituitary

• Serum vasopressin levels low → no production of ADH

• excess renal H20 loss and hypernatremia

• caused by diseases, tumors, or trauma that affects hypothalamus & pituitary stalk (sarcoidosis, anoxia,, hemorrhage)

Central DI

What is the treatment for central DI?

Replete ADH- desmopressin acetate

What condition?

• medullary collecting tubule unresponsiveness to ADH

• adequate or high levels of circulating ADH

• excess renal H20 loss and hypernatremia

• causes: any dz that harms kidney

Nephrogenic DI

What is the treatment for nephrogenic DI?

HCTZ, indomethacin

What serum K+ level indicates hypokalemia and suggests low total body potassium?

< 3.5 mEq/L

What causes hypokalemia?

Dec dietary intake, diuretics (MC), insulin/DM, alkalosis, hypomagnesemia, hyperaldosteronism

How do loop and thiazide diuretics affect potassium?

Inc Na reabsorption in exchange for K and H+ which are lost in urine (increases K loss)

What serum K levels indicate hyperkalemia?

> 5.5 mEq/L

What causes hyperkalemia?

Excess dietary intake, metabolic acidosis, insulin def, heparin, digoxin, cyclosporine, ACEis, K sparing diuretics, dec excretion from renal failure or hypoaldosteronism

What are symptoms of hyperkalemia?

Muscle weakness, cardiac arrhythmias/arrest, often fatal if not corrected

How does renal tubular acidosis affect bicarbonate?

Failure to reclaim HCO3

What is the formula for calculating the anion gap (AG)?

Na⁺ - (Cl^- + HCO₃^-)

What is a normal AG?

10

What would cause a low AG (rare)?

MM or lab error

What is the MUDPILES mnemonic for high AG metabolic acidosis?

Methanol ingestion

Uremia- inc BUN

DKA

Paraldehyde or phosphates

Iron, ischemia, or isoniazid

Lactic acidosis

Ethanol & ethylene glycol

Salicylates & starvation

What is the HARDUP mnemonic for normal AG metabolic acidosis?

Hyperalimentation

Acetazolamide

RTA

Diarrhea

Ureteroenteric fistula

Pancreatic fistula

What should always be looked at when determining type of fluids to administer?

Water & volume status

What are indications for IV fluids?

Shock, hemorrhaging, burns, volume depletion

When would crystalloid IVFs be used?

Fluid deficit, third space losses, maintenance (not used for large replacements)