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Incoming links: Orthostatic proteinuria
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:
- In diabetes, an excessive filtered glucose load can exceed recovery by the proximal tubule. Persistent glycosuria with measured hyperglycaemia, thirst, excessive urination and loss of body mass has much greater diagnostic significance than one weak urinary reaction.
- Transient hyperglycaemia during acute stress or illness can produce transient glycosuria. Changes after a large carbohydrate load depend on the individual's renal handling; a positive sample does not by itself establish chronic diabetes.
- In renal glycosuria, impaired tubular recovery permits loss despite an ordinary blood glucose level. This may be an isolated inherited trait or accompany wider proximal tubule dysfunction, as in Fanconi syndrome or tubular injury. Pregnancy can also lower the effective threshold for urinary loss.
- A specimen can contain other reducing substances, including sugars other than glucose. A general reducing test therefore needs chemical confirmation before its result is labelled glycosuria.
Modern glucose-specific assays and concurrent blood glucose measurements distinguish excess filtered load from reduced recovery.[ref]
Glucosuria in Clinical Methods. Technique, nonspecific copper reduction; Basic Science, glucose load, tubular defects and pregnancy
[ref]Renal Glucosuria by Merck Manual Professional Edition. Definition and causes, isolated transport defect versus generalized tubular dysfunction
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]
Proteinuria by Merck Manual Professional Edition. Pathophysiology; Etiology; functional and orthostatic proteinuria
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]
Proteinuria in Clinical Methods. Technique and Basic Science, precipitation versus protein identification
[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]
Albuminuria: Albumin in the Urine by NIDDK. Detection by dipstick and urine albumin and creatinine measurement
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.