Non-Protein Nitrogens (NPNs)

NPNs arise from …

Catabolism (breakdown) of proteins + nucleic acids into simpler molecules that contain nitrogen but are NOT part of the protein molecule → NPNs

What organ regulates NPNs?

Kidneys filter + remove NPNs from plasma

Specimen containing NPNs

Plasma/Serum or Urine

Importance of NPNs in clinical testing 

NPNs used to evalute Kidney / Renal Function → GFR = glomerular filtration rate

NPN present in Highest conc. in blood + urine = 

UREA (40-50% of total plasma NPNs + 86% of total excreted nitrogen)

BUN =

Blood Urea Nitrogen

Urea production

PROTEIN metabolism

amino acids combined w/ ammonia to form Urea in Liver (UREA CYCLE)

Urea cycle

Liver : Free ammonia + amino groups (protein metabolism) → Urea

Urea travels thru blood to Kidneys

Kidney : Filters MOST Urea out of plasma + most excreted as Urine

Why is Urea cycle so important? 

Without production of Urea, Free Ammonia accumulates in blood leading to toxic effects + CNS / Brain damage

Nitrogen balance depends largely on ___ levels

Urea (47% Nitrogen)

Urea levels depend on …

Diet → Protein intake

• less protein = less urea

Filtrate flow thru kidneys

• Slow flow = MORE reabsorption into plasma

• Fast flow = LESS reabsorption + MORE excreted in urine

T/F: Most Urea is reabsorped in the kidneys

False - Most urea is FILTERED ; only a little urea is reabsorbed (depends on filtrate flow)

Importance of testing Urea

Evaluate Renal function 

Monitor Dialysis

Nitrogen Balance

Azotemia =

increased urea in blood (> 20 mg/dL)

Uremia

Increased urea in blood plus renal failure

(more severe azotemia)

Prerenal Azotemia caused by …

increased blood urea due to issue BEFORE urea reaches kidneys

• Increased Protein Intake / Breakdown

• Decreased blood flow to kidneys

Renal Azotemia caused by …

increased blood urea due to Kidney issue

• Decreased urea filtration

  • Acute / Chronic Renal Failure

  • Renal Disease (Glomerulonephritis, Tubular necrosis)

Postrenal Azotemia caused by …

increased blood urea due to issue AFTER urea exits kidneys

• Urinary Obstruction

  • Renal calculi

  • Bladder / Prostate Tumors

  • Severe UTI (E. coli ; inflammation blocks urine flow)

Conditions causing decreased blood flow to kidneys

Dehydration, Hemorrhage, CHF, Shock

(causes of PRErenal Azotemia)

Increased urea due to Muscle wasting would fall under which category?

• Prerenal azotemia

• Renal azotemia

• Postrenal azotemia 

Prerenal azontemia

muscle wasting causing increased protein breakdown

more protein metabolized = more urea

What causes Decreased plasma urea?

Liver disease

Low protein intake

Late pregnancy

Severe vomitting, diarrhea

How does liver disease affect urea and ammonia?

Liver produces urea from free ammonia + amino acids (protein)

Damaged liver can’t make urea = Decreased urea + Increased ammonia in blood

Creatinine produced from …

Waste product from Creatine oxidation / MUSCLE metabolism

Is creatinine concentration generally high or low in blood?

Majority of creatinine FILTERED by glomeruli 

Minimal reabsorption 

• Low Plasma levels

• HIGH Clearance / High Urine levels 

Creatinine levels determined by…

• Muscle mass → produced from MUSCLE metabolism 

• Creatine turnover

  • NOT affected by Diet / Creatine supplements 

• ★ GFR (Glomerular Filtration Rate)

T/F: Diet / Creatine supplements will increase serum creatinine concentrations

False - Creatine supplementation has minimal effect on serum creatinine concentrations in healthy adults

Which analyte is the most SPECIFIC measurement of Glomerular Function?

Creatinine

What is used to estimate glomerular filtration rate → ★ eGFR ★

Serum Creatinine concentration

Why is creatinine tested?

• Most Specific measurement of Glomerular / Renal Function

• Follow progression of Renal Disease (5 stages of CKD based off GFR)

• Must be evaluated BEFORE CT scan dye administered

What can falsely affect Creatinine levels?

Icterus (bilirubin in blood)

Does a high or low Serum Creatinine indicate an issue?

HIGH SERUM Creatinine indicates Renal / GFR issue

• kidneys should filter most creatinine out as urine, more in blood = kidneys NOT filtering properly / more creatinine reabsorption occuring

Causes of Elevated serum Creatinine

• Decreased GFR

• Renal Disease

• Urinary Obstruction

How much kidney function must be lost before Creatinine levels increase?

Must lose at least 50% of kidney function BEFORE see any increase in Creatinine

What is Clearance?

Measure of how well kidneys function at filtering / “clearing” chemicals out of plasma + into urine per unit time

Used to detect how much plasma is being filtered by kidneys per unit time by comparing serum + urine concentrations of a particular analyte (Inulin, Creatinine)

Clearance units

mL / min.

Specimen used to calculate Clearance

Serum + 24 hr. Urine

Intrinsic Clearance =

Kidney Clearance measured by chemicals intrinsic to body → Creatinine 

Extrinsic Clearance =

Kidney Clearance measured by chemicals extrinsic / foreign to body → Inulin 

“Gold-standard” for measuring Clearance / GFR

Inulin Clearance = “GOLD-standard” 

• Extrinsic chemical → body naturally has NO inulin, NO reabsorption occurs, so kidneys should FILTER OUT ALL of the inulin injected

• Compare serum + urine inulin concentrations

  if inulin excreted does not equal amount injected into patient, means less plasma is being filtered 

Why is Creatinine the next best measurement of Clearance?  

★ Creatinine Clearance = MOST sensitive measure of kidney function  (after than inulin)

• Creatinine is steadily produced + readily excreted by kidneys

  • only a small amount reabsorbed 

Equation to calculate CrCl

Normal Creatinine Clearance range

88-137 mL/min

(Females slightly lower than males)

Does a high or low Creatinine Clearance (CrCl) indicate an issue? What can cause this result?

LOW CrCl = LESS creatinine being FILTERED out into urine / increased creatinine reabsorbed into blood

• Decreased GFR due to Acute / Chronic Glomeruli damage

What Creatinine Clearance value indicates mild, moderate, and severe renal impairment ?

Renal Impairment	Mild	Moderate	Severe
Creatinine Clearance (mL / min.)	50 - 79	10 - 49	< 10

First Step in calculating Creatinine Clearance

Calculate V (volume of urine)→ Convert 24 hr. Urine Volume into mL / min

• Divide total 24 hr. Urine volume by 1440 min. in 24 hrs

What factor must be taken into account in order to accurately calculate Creatinine Clearance?

patients’ BSA (Body Surface Area)

• calculate BSA using pt Height + Weight

• OR use Nomagram

multiply original equation (UV / P) by ( 1.73  m² / BSA m² )

• 1.73 m² = average adult BSA

Modification of Diet in Renal Disease (MDRD) equation

equation used to calcuate eGFR using

• Serum creatinine concentration 

• Age

• Gender

• Ethnicity 

Issue w/ MDRD equation

uses Ethnicity to calculate eGFR

OVERestimates GFR in Black pop. which UNDERestimates progression of kidney disease

Cystatin C

small protein that functions as cysteine protease inhibitor

used to detect decreased GFR

• High blood levels = Low GFR
  

• eliminated exclusively by glomerular filtration

• Produced by cells at constant rate 

• Not altered by age, sex, nutrition 

How do Azotemia conditions affect BUN : Creatinine Ratio?

Azotemia Condition	Ratio	Description
Pre-Renal	↑	BUN ↑ Creatinine N
Renal	N	BUN + Creatinine  ↑ proportionally
Post-Renal	↑	BUN ↑↑ Creatinine slightly ↑

Uric Acid produced by..

Purine metabolism

• purines = nucleotides

• uric acid waste product of cell turnover / DNA breakdown

“Alert” / “Critical” Uric Acid value

> 10 mg/dL

(normal = 3.5 - 7.2 mg/dL)

Increased Uric Acid due to ___ or ____

Increased Production OR Decreased Excretion of Uric Acid   

Conditions associated w/ elevated uric acid

• Idiopathic Gout

• Renal calculi (kidney stones)

• Cancer (leukemia)

  • increased cell turnover = increased DNA breakdown + purine release = increased purine metabolism into uric acid

• Renal Failure 

• Acute Infxn

• Inherited Purine disorders

Gout

increased uric acid in plasma deposits around joints (commonly big toe) + develops sharp, painful Uric acid crystals

Gout usually develops in what population?

What are some risk factors?

Older Males diagnosed between 30-60 yrs old

• Alcohol consumption

• Purine-rich diet

Ammonia formed from…

Amino Acid breakdown + Bacterial metabolism 

Ammonia metabolized by what organ?

Liver - turns ammonia + amino groups into Urea (Urea Cycle)

Ammonia Elevations most commonly caused by …

Severe Liver disease 

• Liver makes urea from free ammonia → liver disease = decreased urea synthesis → leaves incr. Ammonia in body

Effect of increased ammonia 

Ammonia = Toxic to CNS (brain)

What can interfere w/ ammonia results?

• Smoking several hrs prior to blood collection contaminates sample

• Hemolysis falsely increases ammonia (2-3x more ammonia in RBCs than plasma)

How should Ammonia samples be transported + processed?

Collect samples on ice + process w/in 20 min. 

First sign of glomeruli damage =

Leaking protein into urine

Loss of protein in blood results in …

Decreased osmotic pressure → water leaks out of cells into interstitial space (between tissues) → Edema

Glomerular Disease

Acute or Chronic damage to the glomeruli = filtering unit of nephron (kidneys)

Acute Glomerulonephritis (AGN)

Acute = Rapid onset of symptoms

Glomerulonephritis = damaged glomeruli

AGN most commonly affects what population?

Childen + Young adults

AGN caused by…

GAS infxn (Group A Streptococcal)

• Circulation of immune complexes trigger inflammatory response in the glomerular basement membrane → temporary leakage of protein in urine

Toxins / Drugs. Acute kidney infxns, Systemic / Autoimmune diseases

Key symptoms of AGN (Acute Glomerulonephritis)

Rapid Onset of …

• Proteinuria

  • Na+ and H2O retention

  • Edema

  • Hypertension

• Hematuria

• Oliguria (low urine output)

AGN Lab Results

• Proteinuria

• Hematuria

• Decreased GFR

• Increased BUN + Creatinine

• Urine Casts

AGN + CGN stand for …

AGN = Acute Glomerulonephritis

CGN = Chronic Glomerulonephritis

CGN

Chronic Glomerulonephritis

• End stage of persistant glomerular damage

• Irreversible renal tissue loss

• results in Renal Failure

Nephrotic Syndrome

Increased permeability of GBM (glomerular basement membrane)

• causes kidneys to “leak” protein + lipids in urine

• causing not enough protein in blood (Hypoalbuminemia)

Causes of Nephrotic Syndrome

• Glomerulonephtritis complications

• Circulatory disorders affecting Kidneys

Key lab findings in Nephrotic Syndrome

• Massive Proteinuria (>3 g/day)

  • Albuminuria (>1.5 g/day)

  • Hypoalbuminemia

  • Pitting Edema

• Lipiduria (Oval fat bodies in urine)

  • Hyperlipidemia

    • liver nonspecifically increases lipid production due to excess loss of proteins + lipids

What condition is associated w/ Massive Proteinuria, Hypoalbuminemia, Hyperlipidema, Pitting Edema, and Oval fat bodies in urine?

Nephrotic Syndrome

• increased GBM permability allows LOTS of protein + lipids to leak out into urine

What condition is associated w/ Proteinuria, Hematuria, Oliguria, Edema, Hypertension, Decreased GFR, Increased BUN + Creatinine, and Casts in urine ?

Acute Glomerulonephritis (AGN)

Dmaged glomeruli =

• decreased GFR = low urine output ; casts form

• proteins + RBCs leak into urine

• Decr. Urea + Creatinine filtration = Increased serum levels

Pyelonephritis =

Acute vs Chronic =

Kidney inflammation / infection caused by UTI

• Acute = non-permanent damage

• Chronic = permanent damage, possible renal failure

Cystitis =

Bladder inflammation / infection caused by UTI

UTI Lab results

• Pos. Nitrite on urine dipstick

  • common bacteria causing UTIs = Enterobacteriaceae = mostly all convert nitrate to nitrite

• Hematuria

• Pyuria

• WBC Casts

Causes of Renal Obstructions

• Renal Calculi (stones)

• Tumors

• Urethral strictures

Most common cause of Renal Calculi

Calcium oxalate

GFR in Acute Renal Failure

GFR < 10 mL/min

2 most common conditions associated w/ CKD =

Hypertenstion + Diabetes

Complications of CKD

• Anemia

  • kidneys secrete EPO

  • decr. kidney function = decr. EPO = decr. blood cells

• Vit D deficiency

  • kidneys convert calcidiol into calcitriol (active Vit D)

• Mineral + Bone disorders

  • kidneys increase calcium reabsorption

• Hyperparathyroidism

  • due to kidney damage causing less Vit D produciton + Less Calcium reabsorption , Parathryoid glands secreate more PTH to increase Calcium in blood

Stage 1 of CKD

Kidney damage w/ normal - increased GFR > 90 mL/min.

Stage 2 CKD

Kidney damage w/ normal - decreased GFR (60-89 mL/min.)

Stage 3A + 3B CKD

3A = Moderate - Decreased GFR (45-59 mL/min.)

3B = Modertate - SEVERELY Decreased GFR (30-44 mL/min.)

Stage 4 CKD

Severely Decreased GFR (15-29 mL/min.)

Stage 5 CKD

Kidney FAILURE = GFR < 15 mL/min.

Normal GFR

90 -120 mL/min/1.73 m²

CKD staging is dependent on what measurment?

GFR

• As Chronic Kidney disease progresses, GFR gradually declines

Hemodialysis

removal of waste from blood

Hemofiltration

ultrafiltration of blood

decreases fluid volume

 For patients with kidney failure, ____ are the only options

dialysis and/or kidney transplant