The diagnosis is established by the detection of eggs in the stools or urine, with or without concentration techniques. The weight of a stool specimen that can be examined by direct microscopy is approximately 2 to 4 mg. In view of the small volume, therefore, egg excretions of up to 100,000 eggs per day can be missed. Only severe infections are detected in this way. The Kato-Katz method (cellophane impregnated with glycerol and malachite green) uses a larger quantity of stool (25 to 50 mg). The method is simple and more sensitive, but somewhat more cumbersome. Low-grade infections can still be missed. Concentration can be done by a range of techniques. The specificity of the parasitological diagnosis is satisfactory. The distinction between living and dead eggs can be important, e.g. in order to study the efficacy of a treatment. In most cases the morphological aspect is sufficient but, if necessary, a test of eclosion of the eggs can be performed in an attempt to detect the presence of living miracidia after dilution of the urine or stool with fresh water.

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The sensitivity of the laboratory tests is a more serious problem. It is dependent on the quantity of sample which it is feasible to routinely examine. A sample of 10 ml urine is equivalent to approximately 1/100 of the daily production and thus theoretically makes it possible to detect even a mild infection if it is assumed that at least 100 eggs/worm pair/day are found in the urine. With more than 50 eggs/10 ml there is almost always haematuria and proteinuria and has therefore been taken as the accepted threshold for distinguishing between mild and more severe infections. A stool smear, by contrast, examines only 2 mg out of a total quantity of faeces which, for an adult in a tropical environment, may be estimated as 200-400 g/day. In this case therefore only 1/100,000 - 1/200,000 of the daily quantity of stool excreted is examined. An egg load of more than 100 eggs/g is the normally accepted borderline between mild and moderate infection. This is equivalent to more than 5 eggs/Kato, but such infection cannot be detected with a normal smear. With more than 400 to 800 eggs/day, depending on the investigators, the infection is considered severe. One-third of these severe infections can be missed if one uses a single stool smear. For this reason the WHO recommends the Kato method, with which it is possible to examine 25 to 50 mg of stools, sufficient to discover all severe infections. It is, however, clear that even with this technique many milder infections are missed. It is important that a positive smear always indicates an infection which is already fairly severe. There are several other flotation and sedimentation concentration methods which allow detection of lighter degress of infection.

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The sensitivity is also affected by fluctuations in the quantity of eggs in the excreta. This is the case for excretion of S. haematobium eggs, which peaks around midday. Specimens taken between 10 a.m. and 2 p.m. are therefore optimal for examination. During the evening hours and the night, elimination falls to a minimum. This periodicity is the result of contractions of the muscle wall of the bladder, which itself is affected by drinking/meals and exercise, and not by the production of eggs (which occurs continuously). In the case of intestinal schistosomiasis, this systematic factor has little if any importance. An additional source of error is that the elimination of eggs in the same person can vary considerably from day to day, making the individual diagnosis more difficult. The consequence is that a negative parasitological examination, even with sensitive techniques, is only of limited value. In a severely infected person, however, high egg loads are found on average and only rarely low egg loads. The opposite is true for people with low worm loads. Taking faecal specimens on different days is better than examining several smears from 1 stool.

Serology, based on the detection of antibodies, does not distinguish between active and previous infections. Positive serological tests with low titres which cannot be confirmed parasitologically probably indicate either (1) an old, cured infection, (2) an infection with a very low worm load, (3) an infection by worms of a single sex or (4) cross-reactivity with other worm species.

Circulating antigen detection tests (circulating anodic and cathodic antigen) are promising. Antigen can be detected in serum as well as in urine (in urine also for S. mansoni).

As a result of the inflammation in the bladder wall, a large number of eosinophils are found in this organ. The granules of these cells contain various substances that can be released. There is a fairly good correlation between the degree of inflammation of the bladder and eosinophiluria, measured as the concentration of "eosinophilic cationic protein" in the urine. This technique, however, should still be considered experimental.

Complications can be detected by means of ultrasound (e.g. hydronephrosis). The degree of liver involvement can also be determined echographically. This may be of epidemiological importance, for example, in control programmes. Ultrasound is the only possible technique for establishing a non-invasive, sensitive and specific diagnosis of hepatic lesions in hepato-intestinal schistosomiasis. The lesions are pathognomonic and can even be seen in children with surprisingly low egg excretion. There is a clear relationship between the presence of ultrasound lesions and the mean excretion of eggs. A distinction must be made between Symmers fibrosis caused by schistosomiasis and hepatic cirrhosis due to other reasons, but incidentally associated with schistosomiasis. The clinical signs and symptoms are similar. Symmers hepatic fibrosis can become symptomatic in later life when the parasite load has become low and it can even be difficult to detect that there is an infection. Clinical differences between cirrhosis and Symmers hepatic fibrosis are relative: youth of the patients, more pronounced splenic enlargement in Symmers hepatic fibrosis, general health preserved for longer, even after haematemesis, hepatic enlargement, predominantly of the left liver lobe.

Usually, bladder calcifications are visible on a standard radiograph of the abdomen and on CT-scan.

Rectal snip or rectal biopsy consists in removing 1 to 3 fragments of superficial tissue with biopsy forceps under endoscopic control from sites where small haemorrhages or other suspicious lesions are seen. These tissue specimens are placed between two glass slides and examined immediately in a drop of water without fixation. Histological examination has a lower diagnostic yield, as the section of tissue examined is much thinner. The sensitivity of a rectal snip is good and, curiously, better for S. haematobium than for S. mansoni. In travel medicine, this examination is more sensitive, particularly in the case of S. haematobium, than examination of the urine or stools, because the patients involved are mainly adults with a low worm load with few eggs. Rectal snip detects eggs that have accumulated over a period of weeks or months under the rectal mucosa. The distinction between dead and living eggs is important. When living eggs are examined immediately after sampling in an unstained biopsy, the moving cilia of the miracidia can easily be seen. The rectal biopsy technique is not used so often in endemic areas where attention is directed particularly to children. Rectal snip data are not quantitative.

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Other biopsies: Needle biopsy or surgical biopsy of the liver cannot confirm the diagnosis in all cases and is dangerous in patients with a bleeding tendency. Eggs are sometimes found in skin, cervix or bladder biopsies.