Approach to Proteinuria and Hematuria in General Practice

Transcription

1 Approach to Proteinuria and Hematuria in General Practice by Dr. CHOI Kin MB, BS(HK), LMC(Canada), LRCP(London), MRCS(England), MRCP(UK), FRCP(Ireland), FHKCP, FHKAM(Medicine), FACTM, FRACGP, FHKCFP, FHKAM(Family Medicine), DFM(CUHK), DOM(CUHK), DCH(London), P.Dip.Infect.D.(HKU) Specialist in Nephrology Consultant in Family Medicine (PT), Our Lady of Maryknoll Hospital Adjunct Associate Professor in Family Medicine, CUHK Honorary Clinical Assistant Professor in Family Medicine, HKU Examiner, HKCFP, RACFP Assessor, Exit Examination for FJKAM(Family Medicine) Urinalysis and Urine Microscopy Dipstick urinalysis cost less than $1 and should be considered more frequently in clinical examination, just like taking a BP. Many brands of dipsticks are available and it is important to know which one is being used. Blood - relies on the presence of hemoglobin. Discrete, punctate colour changes indicates the presence of red cells, whereas diffuse colour change may indicate free hemoglobin. Myoglobin cross-reacts in the assay. A strongly positive dipstick test for blood with muddy brown urine with no red cells visible on microscopy suggests myoglobinuria. False + by contamination with iodine or hypochlorite. Bacterial peroxidase may cause + test. The most common cause of a positive dipstick test with negative urine microscopy is lysis of red cells while awaiting urine microscopy. Protein dipstick test utilizes a ph-sensitive indicator, buffered within the strip, whose colour-change point is altered by proein binding. The test is sensitive to albumin, but other urinary proteins as light chains do not produce a colour change. A protein concentration of around 300 mg/l is required for a colour change. Normal urine contains a small amount of protein, so highly concentrated urine may cause a 1+ reaction. Bacterial urine infection may produce a positive test. Strongly + tests always indicate renal disease. False positive occurs if ph is less than 7. Knowledge of urine ph is rarely helpful. Alkaline urine in infection with urease producing organisms as Proteus, which cause infection stones. Urine ph>5.3 in the presence of systemic acidosis is diagnostic of renal tubular acidosis. Nitrite is positive in urine infection, but not all organisms produce nitrite. Leucocyte esterase detects pyuria, usually present in significant urine infection. Specific enzymatic assays for albumin in dipstick is used for detection of microalbuminuria mg/24 hours

2 Urine microscopy the Liquid Biopsy. Pyuria- usually in infected urine. Sterile pyuria in chlamydial lower UTI, partially treated UTI, papillary necrosis, stones or renal TB. Eosinophiluria in acute interstitial nephritis require staining. Epithelial cells- larger than leucocytes and shed in increased numbers in acute tubular necrosis. Red cells- Usually recognized as biconcave disk. Glomerular bleeding results in shrinkage and deformity of the cells as they pass through the loop of Henle. Casts Hyaline casts are formed by precipitation of Tamm-Horsfall glycoprotein, a component of normal urine, within the tubular lumen. Increased numbers seen after diuresis. Glomerular casts are casts of cell debris and are abnormal. White cell casts are diagnostic of acute pyelonephritis. Red cell casts are diagnostic of the presence of red cells within the tubules, indicating glomerular hematuria. Broad or waxy cast are formed in dilated atrophic tubules and indicate chronic renal disease. Hematuria In all humans some erythrocytes leak into the urine. In healthy individuals, counts in MSU samples are less than 1.3 x 10^7 cells/l and the morphologic pattern is always glomerular (pleomorphic). Increased hematuria is a common presenting sign in urinary tract disease. It may be macroscopic or microscopic. Hematuria is visible macroscopically when urinary red cells exceeds 5 x 10^9 cells/l. Counts in the range 2 x 10^7 to 5 x 10^9 cells/l are detectable by microscopy and dipstick. Counts of less than 2 x 10^7 cells/l are detectable by microscopy only A few red cells are found in normal urine, especially in female, but a pathological cause can nearly always be found for hematuria sufficient to be detected on dipstick testing or routine microscopy. However, microscopic hematuria is very common and exhaustive investigations is not always necessary. Macroscopic hematuria is obvious, but can be confused with severe hemaglobinuria or myoglobinuria or beeturia. Dipstick test is used in screening. Positive tests are caused by hematuria, detection limit being 5 cells/ul. Hemoglobinuria and myoglobinuria also give a positive result. False positive is caused by iodine contamination of the sample container. Positive dipstick for hematuria with negative microscopy are more usually due to false negative microscopy. With bright field microscopy, negative results may occur as a result of spontaneous lysis of red cells or by failure to detect ghost forms. Phase contrast microscopy need a fresh specimen, is more time-consuming and more sensitive for the detection of low grade hematuria and differentiation of glomerular and non-glomerular hematuria. The microscopic analysis of hematuria involves 3 steps: - 2 -

3 1) determination of cell counts 2) assessment of the pattern of cell morphology 3) a search for other evidence of renal parenchymal disease. Counting cells Cell counts should be standardized since the normal range depends upon the type of microscopy and the nature of samples. Urine sediment Bright field microscopy <8 x 10^5 cells/l Urine sediment Phase-contrast microscopy <8 x 10^6 cells/l Uncentrifuged urine Phase-contrast microscopy <1.3 x 10^7 cells/l Cell counts should be determined with a counting chamber. Semi-quantitative cell counts (i.e. counts per high power field) do not accurately reflect the number of cells in the sample. Cell counts should be performed on uncentrifuged urine. At least 50 cells or the cells in five large squares of a modified Fuchs-Rosenthal counting chamber should be counted and then calculated. The urine sediment should be obtained by centrifugation and examined for casts and fat droplets, and to determine the pattern of erythrocyte morphology in the samples with low cell counts. The volumes of sample and deposit should be standardized: Pour 10 ml of a well-mixed sample into a graduated centrifuge tube. Centrifuge at 1500 rpm in a bench top centrifuge with a swing-out head for 5 minutes (750g). Aspirate the supernatant at the meniscus to the 0.5 ml. mark. Re-suspend the deposit in the remaining 0.5 ml of urine. Examine the resuspended deposit in a counting chamber. The site of bleeding can be identified as glomerular or non-glomerular by assessing the pattern of erythrocyte morphology. At the first visit, this helps determine the direction of further investigation without the unnecessary cost and inconvenience of inappropriate and often invasive diagnostic procedures. Non-glomerular bleeding should be referred for urological investigation while glomerular bleeding referred for nephrologist. Non-glomerular bleeding is indicated by a uniform erythrocyte morphology (one or two morphologic cell types only) Because normal urine contains up to 1.3 x 10^7 glomerular red cells per litres, some cells of a pleomorphic nature are seen but are usually obscured by large numbers of uniform cells in nonglomerular bleeding. Glomerular bleeding is indicated by a marked variation in red cell morphology (pleomorphic, at least 3 different sizes or shapes) and in haemoglobin concentration. Samples that contain clear evidence of increased glomerular bleeding but in which a significant number of cells have a uniform morphology suggest the presence of two source of bleeding and hence 2 diagosis. Other evidence of glomerular bleeding Patients with glomerular bleeding shed other evidence of glomerulnephritis into the urine which depends in part upon the nature and severity of the glomerular lesion

4 1) Erythrocyte casts 2) Erythrophagocyes 3) Proteinuria: It is frequently asserted that proteinuria may result from non-glomerular haematuria. However, one litre of urine with an erythrocyte count of 5 x 10^9 (i.e. clearly showing macroscopic haematuria) contains the erythrocytes from 1 ml of whole blood. If the blood has a PCV of 45 and a plasma protein concentration of 80 g/l, the litre of urine will contain 44 mg. protein (55% of 80 mg) which gives a negative or only a trace reaction to protein on the dipstick. A finding of more than a trace reaction for protein on the dipstick in a sample with microscopic hematuria probably indicates a renal parenchymal lesion. Some experts are critical of the value of urine red cell morphology. Ward & Kaplan published in the Journal of Urology 1998 October issue on the refined microscopic urinalysis for red blood cell morphology in the evaluation of asymptomatic microscopic haematuria in a pediatric population. They found that the sensitivity of dysmorphic RBC in predicting glomerular bleeding was 83% and specificity 81%. However, for isomorphic RBC, the sensitivity was only 25% and specificity 22% for predicting non-glomerular bleeding. Hematuria and 2+ proteinuria were more sensitive (100%) and specific (83%) in predicting glomerulonephritis. Although Oxford Textbook of Medicine suggested that a cut-off of 80% or more of cells being dysmorphic correlates quite closely with a glomerular source of blood loss while less than 20% of dysmorphic cells is usually associated with a non-glomerular disease. It appears that red cell dysmorphism may more precisely reflect a renal rather than glomerular source of blood loss, since bleeding caused by renal biopsy was found to be dysmorphic pattern in one study. In experience hands, this non-invasive test may provide a useful guide to the next step in evaluation of a patient with hematuria of undetermined cause. Macroscopic Haematuria Macroscopic hematuria may reflect underlying glomerulonephritis, stone or malignancy. An accurate red cell count is of no importance because the count will be 5 x 10^9 cells/l or more. Macroscopic hematuria due to glomerulonephritis in adults indicates the presence of a crescentic lesion which may be diffuse and is an indication for urgent renal biopsy to establish diagnosis and to make a decision about tratment because crescents destroy glomeruli within days. Patients with a proliferative glomerulonephritis tend to have the highest red cell counts. Counts above 10^9 cells/l usually indicate the presence of crescentic lesions and are often an indication for an urgent renal biopsy. Heavy hematuria (3 x 10^8 to 1 x 10^9 cells/l) may be seen with the familial thin BMD. However, these patients urine has few casts (<250/ml). Causes of hematuria: 1. Urological malignancy. 2. Urothelial inflammation by infection, stone or crystalluria by hypercalcuria. 3. Renal tissue necrosis in papillary necrosis and renal embolism. 4. Anticoagulation. 5. Glomerulonephritis. Hematuria occurs with active inflammation of glomeruli and membranous nephropathy and minimal change disease. Absence of proteinuria does not - 4 -

5 exclude glomerulonephritis. Recurrent macroscopic hematuria shortly after onset of URTI is highly suggestive of IgA nephropathy or mesangiocapillary glomerulonephritis. 6. Renal vein thrombosis. Consider this in a nephritic patient with hematuria with or without loin pain. 7. Polycystic kidneys. 8. Alport s syndrome. 9. Thin basement membrane nephropathy. This is an inherited disease characterized by abnormally thin basement membranes, detection of which require EM. Hematuria may be microscopic, macroscopic or intermittent. Long term prognosis is thought to be good, also called benign familial hematuria, but cases of renal failure have been described. Autosomal dominant. 10. Loin pain hematuria syndrome. Severe loin pain, flank tenderness and hematuria. Rarer in males than females. Non-specific deposition of C3 in arterioles is frequently present. No satisfactory treatment. 11. Sickle cell disease and trait due to sickling in the renal medulla. 12. Severe exercise, even if non-traumatic. 13. Schistosomiasis. 14. Factitious. Investigation: Urological cause or Nephrological cause. Urothelial malignancy is uncommon under MSU and urethral swab to exclude urinary tract infection, a rare cause of asymptomatic hematuria. 2. Urine cytology in those at risk of malignancy. 3. Phase contrast microscopy or automated cell size analysis to distinguish glomerular and nonglomerular bleeding. 4. Test for proteinuria, positive result suggest a renal cause for hematuria. 5. RFT impairment suggest parenchymal disease or bilateral obstruction. 6. IVU- first line investigation for UT abnormalities, including stones and tumours. 7. Ultrasound less reliable for ureteric tumours or stones. 8. Flexible cystoscopy on OP basis to detect bladder tumours

6 9. Renal biopsy for definitive diagnosis of parenchymal renal disease and shows glomerular abnormalities in at least 50% of patients with isolated microscopic hematuria. Biopsy should be performed if result will alter management (seldom the case in the absence of proteinuria or renal impairment), if the prognosis needs to be known (e.g. for insurance purposes), or if a positive diagnosis is necessary to obviate the need for repeated urological investigations. An alternative is to assume that the patient has chronic GN and to arrange annual checks of BP and renal function, with reassessment if either becomes abnormal. Proteinuria Microalbuminuria: increase excretion of albumin below the range normally detectable by standard dipsticks. Clinical proteinuria: detection of proteinuria by dipstick. Macroalbuminuria. Nephrotic range proteinuria >3 g. protein per 24 hours. Tubular proteinuria- excretion of low molecular weight proteins normally reabsorbed by proximal tubules. Bence-Jones proteinuria: excretion of immunoglobulin light chains. Dipstick test: insensitive to light chains and globulin. Detection limit is 300 mg/l. False + in highly alkaline urine (strip uses a ph-sensitive dye buffered at ph 3.0 whose ph sensitivity is altered by proteins); False ve occur in dilute urine. Precipitation method is used in laboratory for quantitative measurement of protein excretion. Expressed in g/24 hours or as protein/creatinine ratio (random sample urine), the latter relying on the fact that creatinine excretion rate is relatively constant. >300 mg/24 hours or 30 mg/mmol creatinine is pathological. Electrophoresis of urine allows qualitative assessment of which proteins are present, detecting tubular protein and polyclonal and monoclonal light chains. Specific assays for albumin and other urinary proteins and enzymes. Sticks are available for microalbuminuria but are observer-dependent and do not allow for variations in urine concentration. Functional proteinuria occur in fever, exercise, congestive heart failure and orthostatic posture. Seldom > 1g/24 hours. Heavy proteinuria predicts progressive renal disease because proteinuria itself causes tubular damage and interstitial scarring. Tubular proteinuria as a result of tubular damage results in the decreased reabsorption of low molecular weight proteins and to a lesser extent, albumin. Increased tubular enzymes are released e.g. N-acetyl-B- D-glucosaminidase. Overflow proteinuria when massively increased filtration of proteins overwhelms the reabsorptive capacity of the tubules. In light-chain overproduction, lysozyme in acute leukemia and amylase in acute pancreatitis

7 Microalbuminuria in diabetic is highly predictive both of increased cardiovascular mortality and of progression in clinical diabetic nephropathy. Early detection and treatment may prevent progression of the nephropathy. Low grade proteinuria: How far to investigate asymptomatic proteinuria 300 mg to 2 g/24 hours is controversial. Postural proteinuria can be excluded by measuring protein excretion rate in urine collected after overnight recumbency. No further investigation if this is normal. Biopsy if hematuria, hypertension or renal impairment. Exclude myeloma in over 40. Attend to cardiovascular risk factors. High grade proteinuria greater than 2 g/24 hours usually indicates significant primary renal disease. Biopsy to exclude treatable causes e.g. SLE, Membranous GN, MCGN, to enable prediction of prognosis. Significant (more than 0.5 g/24 hours) but non-nephrotic (less than 3.5 g/24 hours) proteinuria involves the following differential diagnosis: 1. Beign orthostatic proteinuria 2. Idiopathic glomerular disease (especially in early stages) a) Focal glomerulosclerosis b) IgA nephropathy c) Membranous nephropathy d) Amylodosis 3. Systemic diseases a) Diabetic nephropathy b) Essential hypertension c) Congestive heart failure d) Febrile states - 7 -