Clinical Chemistry

Nonprotein nitrogen compounds in the blood

Urea–> largest component

AA’s, urate, creatinine, ammonia

;– breakdown of protein & nucleic acids

Measurement of BUN

Urea–>urease  ammonium ion

=> calculate [urea]

Hypovolemia and BUN

Urea reabsorption increases

=> BUN underestimates GFR more

Creatinine and GFR

[Creatinine]serum  inverse GFR

–>endogenous–> passes freely through the glomerulus

small amount –> secreted by the tubules=> overestimates GFR

GFR calculation

ClCr = UCr x VUr / PCr

* nonlinearity: ClCr ~ GFR (linear when GFR ~ 1/2 nml)

*Nonglomerular influences–> Creatinine (eg. muscle)


estimated GFR –> age & BW

–> in adult Caucasian and AfricanAm w GFR<60

elevated BUN & creatinine

BUN: Cr = (10-20):1


Renal azotemia

ratio = normal

BUN : Cr > 20:1


Prerenal azotemia<– poor renal perfusion

Postrenal azotemia<– renal obstruction

BUN : Cr < 10:1


Dietary protein insuficiency

Severe liver disease


other for estimating GFR and predict mortality in chronic kidney disease

Cystatin = cysteine protease inhibitor

–>independent of age, sex, nuscle mass

Urine protein tests

Assay–> lower limit ~ 3mg/dL, sensitive to all proteins

Proteinurine: Creatinine ~ 24 hr urine

Urine dipstick–> albumin, lower level ~ 18mg/dL


Tubular dysfunction


beta2-microglobulin & lysozyme

–> freely filtered by the glomerulus

–>completely reabsorbed by proximal convoluted tubule

Which assay can detect as little as 0.3mg/dL of albumin in urine
microalbumin assay –> spot urine

high [Protein]urine

Microalbumin –


Hook effect1 vs. Bence-Jones protein

1falsely low values on an immunoassay when an overwhelming amount of Ag affects the binding capacity of the added antibody

Laboratory screening for Chronic Kidney Disease for high risk groups (DM, HT, Family Hx)


2.microalbuminuria –> 1Albuminurine: Cr

1microalbumin assay

FENa < 1%


prerenal ARF1

Pt on diuretics / w glycosuria 

1FEurea< 35%

Progressive renal impairment in Pt with severe end- stage liver disease.Absence of another identifiable cause of renal disease.


Hepatorenal Syndrome
Most common cause of renal failure in the cirrhotic Pt.
Spontaneous bacterial peritonitis

Cause of HRS

Renal bx findings?

<– following profound fluid shifts eg Rx of ascites=>dysregulation of renal blood flow

Renal bx: normal

*cirrhosis w HV’s –> Glomerulonephritis/ *IgA-like nephropathy


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