Proteinuria

spot or random urine protein/ creatinine ratio of first morning specimen

either 24 hr or spot test :

if >1.5- 2.0g , think Glomerular disease

if <1.0g, think tubulointerstitial disease

Tubular proteinuria is associated with the presence of low molecular weight proteins, such as b2-microglobulin, immunoglobulin light chains, amino acids, and retinol-binding protein. These are normally filtered by the glomerulus and almost completely reabsorbed in the proximal tubule. They appear in urine when the proximal tubular function is disrupted, for instance, in tubulointerstitial nephritis.

Proteins of low molecular weight are normally filtered by the glomerulus and reabsorbed at the proximal tubule, but when these low-molecular-weight proteins are produced in a greater amount. the reabsorptive capacity of proximal tubules is exceeded, and an overload proteinuria occurs. This most commonly occurs in multiple myeloma, when large amounts of immunoglobulin light chains are produced.

Microalbuminuria

Albumin loss with minimal loss of the more bulky proteins (such as lgG and macroglobulin) defines selective proteinuria.

(Minimal change disease is an example of a highly selective proteinuria: mostly low-molecular weight proteins, such as albumin and transferrin, are excreted. )

Def: > 30 mg in a 24 hr urine

albumin/ creatinine ratio: 17-250 mg/g men

25-355 mg/g women

Clinical albuminuria

24hr urine > 300mg/d

Albumin/ creatinine ratio > 250 mg/g men

355 mg/g women

So, roughly, 30-300mg/24 hours is regarded as microalbuminuria

Types of proteinuria