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Excess serum albumin excretion in urine, distinguished from proteinuria due mainly to other proteins.^[ref]

The significance of glycosuria and albuminuria depends on persistence, amount, mechanism and accompanying findings. The older words “sugar” and “albumen” do not guarantee that a nineteenth-century test identified one particular molecule.

For urinary sugar, distinguish the following situations:

Modern glucose-specific assays and concurrent blood glucose measurements distinguish excess filtered load from reduced recovery.^[ref][ref]

For “albumen”, the principal pathological groups are injury to the glomerular filtration barrier in glomerulonephritis, renal amyloidosis, diabetic kidney disease and other glomerular diseases; changes associated with heart failure and renal venous congestion; and pregnancy-associated injury such as pre-eclampsia. Fever and severe exertion may produce transient proteinuria, while orthostatic proteinuria can disappear during recumbency. Impaired tubular recovery chiefly increases smaller urinary proteins; it should not automatically be called a selective loss of serum albumin.^[ref]

A collected specimen can also receive blood plasma proteins from haematuria or inflammatory material below the filtering apparatus. Moreover, immunoglobulin light chains in multiple myeloma can give a positive general protein test without being serum albumin. Historical heat and acid precipitation tested a physical property of material in a tube, not a modern molecular diagnosis.^[ref][ref]

The diagnostic value consequently rises with reproducibility and coherent accompanying evidence. Persistent heavy albuminuria, especially with oedema and abnormal sediment, strongly suggests significant renal disease; red blood cell casts support a renal rather than merely lower-tract source of bleeding. Repeated urinalysis, sediment microscopy and a urine albumin-to-creatinine ratio help quantify and localize the problem.^[ref] Coexisting glycosuria and albuminuria may reflect diabetes with renal injury, or another combination of mechanisms. Neither their coexistence nor either isolated result is sufficient to establish the whole diagnosis.

An albuminous urine specimen can reflect renal leakage, altered renal function, or added blood plasma proteins below the kidney. Finding serum albumin in urine identifies a phenomenon, not a single disease.

In the historical setting, the important group was the renal disorders gathered under Bright's disease: acute inflammatory disease, including that following scarlet fever, and chronic diseased or contracted kidneys. In current terms, glomerulonephritis damages the glomerular filtration barrier, permitting increased passage of serum albumin into the filtrate. Red blood cells and urinary casts may accompany the loss. Different modern glomerular diseases can produce the same finding; the nineteenth-century umbrella does not identify one modern microscopic diagnosis.^[ref]

In renal amyloidosis, deposition in the glomeruli disrupts their filtering structure; heavy albuminuria and nephrotic syndrome may result. Diabetic kidney disease and hypertensive kidney disease provide further modern examples of chronic injury to the filtering apparatus. These modern classifications distinguish mechanisms.^[ref]

The heart failure group includes renal venous congestion and impaired effective kidney perfusion. Altered pressures and injury to the filtering apparatus can increase albuminuria; an albuminous specimen does not by itself prove destructive nephritis. Fever and severe acute illness can also produce transient proteinuria through reversible changes in renal function. In pre-eclampsia, injury to the filtering apparatus, including glomerular endotheliosis, can cause albuminuria.^[ref] Pregnancy alone does not make albuminuria normal, and pressure from a gravid uterus is not an adequate general explanation of this disorder.^[ref]

Finally distinguish renal loss from addition below the filtering apparatus. Haematuria, pyelonephritis, cystitis and contamination by inflammatory or genital material can add blood plasma proteins, including serum albumin, to a collected specimen. Microscopy and a clean sample help distinguish these possibilities. Tubulointerstitial nephritis reduces proximal tubule recovery of filtered proteins, but predominantly causes loss of smaller proteins. Likewise, overflow of immunoglobulin light chains in multiple myeloma is proteinuria, not necessarily albuminuria. Haematuria alone can contribute blood plasma proteins, so modest protein positivity need not locate the bleeding in the kidney.^[ref] The distinction matters because an old protein-precipitation test did not identify the molecular species.^[ref]

A useful diagnostic comparison is repeated urinalysis, with microscopy of the sediment and a modern urine albumin-to-creatinine ratio. Persistence, red blood cell casts, and the clinical setting distinguish sustained glomerular disease from a transient change or lower-tract addition. A positive protein test alone cannot make that distinction.^[ref]