Urea--> largest component

AA's, urate, creatinine, ammonia

<-- breakdown of protein & nucleic acids

Urea-->^urease  ammonium ion

=> calculate [urea]

Urea reabsorption increases

=> BUN underestimates GFR more

[Creatinine]_serum  inverse GFR

-->endogenous--> passes freely through the glomerulus

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

Cl_Cr = U_Cr x V_Ur / P_Cr

_^* nonlinearity: Cl_Cr ~ 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

Dx?

Renal azotemia

ratio = normal

BUN : Cr > 20:1

DDx?

Prerenal azotemia<-- poor renal perfusion

Postrenal azotemia<-- renal obstruction

BUN : Cr < 10:1

DDx?

Dietary protein insuficiency

Severe liver disease

rare

Cystatin = cysteine protease inhibitor

-->independent of age, sex, nuscle mass

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

Protein_urine: Creatinine ~ 24 hr urine

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

Tubular dysfunction

Assays?

beta₂-microglobulin & lysozyme

--> freely filtered by the glomerulus

-->completely reabsorbed by proximal convoluted tubule

high [Protein]_urine

Microalbumin -

DDx

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

1.eGFR

2.microalbuminuria --> ¹Albumin_urine: Cr

¹microalbumin assay

FENa < 1%

ddx?

prerenal ARF¹

Pt on diuretics / w glycosuria 

¹FE_urea< 35%

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

Dx?

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