= Solution
\b[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.<Bright's disease by the University of Leeds Library>[History, the association of dropsy, albuminuria and renal disease]{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.<Proteinuria by Merck Manual Professional Edition>[Etiology, glomerular causes including amyloidosis, diabetic nephropathy and postinfectious glomerulonephritis]{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>.<The glomerular injury of preeclampsia>[Abstract, endothelial swelling and disruption of the filtration apparatus]{ref} Pregnancy alone does not make <albuminuria> normal, and pressure from a gravid <uterus> is not an adequate general explanation of this disorder.<Proteinuria by Merck Manual Professional Edition>[Etiology, preeclampsia; Pathophysiology, functional and tubular proteinuria]{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>.<Hematuria in Clinical Methods>[Clinical Significance, serum proteins accompanying haematuria]{ref} The distinction matters because an old protein-precipitation test did not identify the molecular species.<Proteinuria in Clinical Methods>[Definition and Technique, heat and acid precipitation; Basic Science, glomerular, tubular and overflow proteins; Clinical Significance, urinary sediment]{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.<Albuminuria: Albumin in the Urine by NIDDK>[How is albuminuria detected?, urine albumin and creatinine measurement]{ref}
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