Diagnosis is primarily performed via fine needle aspiration of the lesion of the thyroid to distinguish it from other types of thyroid lesions. Microscopic examination will show amyloid and hyperplasia of parafollicular C cells.

While the increased serum concentration of calcitonin is not harmful, it is useful as a marker which can be tested in blood.

A second marker, carcinoembryonic antigen (CEA), also produced by medullary thyroid carcinoma, is released into the blood and it is useful as a serum or blood tumor marker. In general, measurement of serum CEA is less sensitive than serum calcitonin for detecting the presence of a tumor, but has less minute to minute variability and is therefore useful as an indicator of tumor mass.

According the Fifth WHO Expert Committee on Filariasis , the most common method of classification of lymphedema is as follows: (The same classification method can be used for both primary and secondary lymphedema)

The International Society of Lymphology (ISL) Staging System is based solely on subjective symptoms, making it prone to substantial observer bias. Imaging modalities have been suggested as useful adjuncts to the ISL staging to clarify the diagnosis. The lymphedema expert Dr. Ming-Huei Cheng developed a Cheng’s Lymphedema Grading tool to assess the severity of extremity lymphedema based on objective limb measurements and providing appropriate options for management.

Accurate diagnosis and staging are fundamental to the management of lymphedema patients. A swollen limb can result from different conditions that require different treatments. Diagnosis of lymphedema is currently based on history, physical exam, limb measurements, and imaging studies such as lymphoscintigraphy and indocyanine green lymphography. However, the ideal method for lymphedema staging to guide the most appropriate treatment is controversial because of several different proposed protocols.

Lymphedema can occur in both the upper and lower extremities, and in some cases, the head and neck. Assessment of the extremities first begins with a visual inspection. Color, presence of hair, visible veins, size and any sores or ulcerations are noted. Lack of hair may indicate an arterial circulation problem. Given swelling, the extremities' circumference is measured for reference as time continues. In early stages of lymphedema, elevating the limb may reduce or eliminate the swelling. Palpation of the wrist or ankle can determine the degree of swelling; assessment includes a check of the pulses. The axillary or inguinal nodes may be enlarged due to the swelling. Enlargement of the nodes lasting more than three weeks may indicate infection or other illnesses such as sequela from breast cancer surgery requiring further medical attention.

Diagnosis or early detection of lymphedema is difficult. The first signs may be subjective observations such as "my arm feels heavy" or "I have difficulty these days getting rings on and off my fingers". These may be symptomatic of early stage of lymphedema where accumulation of lymph is mild and not detectable by changes in volume or circumference. As lymphedema develops further, definitive diagnosis is commonly based upon an objective measurement of differences between the affected or at-risk limb at the opposite unaffected limb, e.g. in volume or circumference. No generally accepted criterion is definitively diagnostic, although a volume difference of 200 ml between limbs or a 4-cm difference (at a single measurement site or set intervals along the limb) is often used. Bioimpedance measurement (which measures the amount of fluid in a limb) offers greater sensitivity than existing methods.

Chronic venous stasis changes can mimic early lymphedema, but the changes in venous stasis are more often bilateral and symmetric. Lipedema can also mimic lymphedema, however lipedema characteristically spares the feet beginning abruptly at the medial malleoli (ankle level). Lipedema is common in overweight women. As a part of the initial work-up before diagnosing lymphedema, it may be necessary to exclude other potential causes of lower extremity swelling such as renal failure, hypoalbuminemia, congestive heart-failure, protein-losing nephropathy, pulmonary hypertension, obesity, pregnancy and drug-induced edema.

There are reliable tests for the actual use of alcohol, one common test being that of blood alcohol content (BAC). These tests do not differentiate alcoholics from non-alcoholics; however, long-term heavy drinking does have a few recognizable effects on the body, including:

- Macrocytosis (enlarged MCV)

- Elevated GGT

- Moderate elevation of AST and ALT and an AST: ALT ratio of 2:1

- High carbohydrate deficient transferrin (CDT)

With regard to alcoholism, BAC is useful to judge alcohol tolerance, which in turn is a sign of alcoholism.

However, none of these blood tests for biological markers is as sensitive as screening questionnaires.

The pulmonary embolism rule-out criteria (PERC) helps assess people in whom pulmonary embolism is suspected, but unlikely. Unlike the Wells score and Geneva score, which are clinical prediction rules intended to risk stratify people with suspected PE, the PERC rule is designed to rule out risk of PE in people when the physician has already stratified them into a low-risk category.

People in this low risk category without any of these criteria may undergo no further diagnostic testing for PE: Hypoxia — Sa 50, hormone use, tachycardia. The rationale behind this decision is that further testing (specifically CT angiogram of the chest) may cause more harm (from radiation exposure and contrast dye) than the risk of PE. The PERC rule has a sensitivity of 97.4% and specificity of 21.9% with a false negative rate of 1.0% (16/1666).

In people with a low or moderate suspicion of PE, a normal D-dimer level (shown in a blood test) is enough to exclude the possibility of thrombotic PE, with a three-month risk of thromboembolic events being 0.14%. D-dimer is highly sensitive but not specific (specificity around 50%). In other words, a positive D-dimer is not synonymous with PE, but a negative D-dimer is, with a good degree of certainty, an indication of absence of a PE. The typical cut off is 500 μg/L, although this varies based on the assay. However, in those over the age of 50, changing the cut-off value to the person's age multiplied by 10 μg/L (accounting for assay which has been used) is recommended as it decreases the number of falsely positive tests without missing any additional cases of PE.

When a PE is being suspected, several blood tests are done in order to exclude important secondary causes of PE. This includes a full blood count, clotting status (PT, aPTT, TT), and some screening tests (erythrocyte sedimentation rate, renal function, liver enzymes, electrolytes). If one of these is abnormal, further investigations might be warranted.

Troponin levels are increased in between 16–47% with pulmonary embolism.

Several tools may be used to detect a loss of control of alcohol use. These tools are mostly self-reports in questionnaire form. Another common theme is a score or tally that sums up the general severity of alcohol use.

The CAGE questionnaire, named for its four questions, is one such example that may be used to screen patients quickly in a doctor's office.

Other tests are sometimes used for the detection of alcohol dependence, such as the Alcohol Dependence Data Questionnaire, which is a more sensitive diagnostic test than the CAGE questionnaire. It helps distinguish a diagnosis of alcohol dependence from one of heavy alcohol use. The Michigan Alcohol Screening Test (MAST) is a screening tool for alcoholism widely used by courts to determine the appropriate sentencing for people convicted of alcohol-related offenses, driving under the influence being the most common. The Alcohol Use Disorders Identification Test (AUDIT), a screening questionnaire developed by the World Health Organization, is unique in that it has been validated in six countries and is used internationally. Like the CAGE questionnaire, it uses a simple set of questions – a high score earning a deeper investigation. The Paddington Alcohol Test (PAT) was designed to screen for alcohol-related problems amongst those attending Accident and Emergency departments. It concords well with the AUDIT questionnaire but is administered in a fifth of the time. Certain blood tests may also indicate possible alcoholism.

There are several measures that can be employed to assess the executive functioning capabilities of an individual. Although a trained non-professional working outside of an institutionalized setting can legally and competently perform many of these measures, a trained professional administering the test in a standardized setting will yield the most accurate results.

The Clock drawing test (CDT) is a brief cognitive task that can be used by physicians who suspect neurological dysfunction based on history and physical examination. It is relatively easy to train non-professional staff to administer a CDT. Therefore, this is a test that can easily be administered in educational and geriatric settings and can be utilized as a precursory measure to indicate the likelihood of further/future deficits. Also, generational, educational and cultural differences are not perceived as impacting the utility of the CDT.

The procedure of the CDT begins with the instruction to the participant to draw a clock reading a specific time (generally 11:10). After the task is complete, the test administrator draws a clock with the hands set at the same specific time. Then the patient is asked to copy the image. Errors in clock drawing are classified according to the following categories: omissions, perseverations, rotations, misplacements, distortions, substitutions and additions. Memory, concentration, initiation, energy, mental clarity and indecision are all measures that are scored during this activity. Those with deficits in executive functioning will often make errors on the first clock but not the second. In other words, they will be unable to generate their own example, but will show proficiency in the copying task.